Weinans, H.H.

Unfocused extracorporeal shock waves induce anabolic effects in osteoporotic rats (Article)

2013-05-01T00:00:00Z

Unfocused extracorporeal shock waves (UESW) have been shown to have an anabolic effect on bone mass. Therefore we investigated the effects of UESW on bone in osteoporotic rats with and without anti-resorptive treatment. Twenty-week-old rats were ovariectomized (n = 27). One group was treated with saline and another group with Alendronate (ALN) 2.4 μg/kg, 3×/week. UESW were applied 2 weeks after ovariectomy. Thousand UESW were applied to one hind leg, the contra-lateral hind leg was not treated and served as control. With the use of in vivo micro-CT scanning it was shown that in saline treated rats trabecular bone volume fraction (BV/TV) was higher at 2 weeks follow-up in UESW treated legs compared to control legs. However, at 4 and 10 weeks no difference was found. In ALN treated animals UESW led to a pronounced anabolic response resulting in an increase in BV/TV at all time-points. Furthermore, UESW resulted in increased cortical volume (CtV), higher trabecular connectivity and, more plate-like and thicker trabeculae. Biomechanical testing showed that UESW lead to a higher maximum force before failure and higher stiffness in all treatment groups. With histology abundant areas of intramembranous bone formation along the periosteal cortex and within the bone marrow were observed. In conclusion this study shows promising results for the use of UESW in the treatment of osteoporosis, especially when this treatment is combined with an anti-resorptive treatment. Copyright

Selective laser melting-produced porous titanium scaffolds regenerate bone in critical size cortical bone defects (Article)

2013-05-01T00:00:00Z

Porous titanium scaffolds have good mechanical properties that make them an interesting bone substitute material for large bone defects. These scaffolds can be produced with selective laser melting, which has the advantage of tailoring the structure's architecture. Reducing the strut size reduces the stiffness of the structure and may have a positive effect on bone formation. Two scaffolds with struts of 120-μm (titanium-120) or 230-μm (titanium-230) were studied in a load-bearing critical femoral bone defect in rats. The defect was stabilized with an internal plate and treated with titanium-120, titanium-230, or left empty. In vivo micro-CT scans at 4, 8, and 12 weeks showed more bone in the defects treated with scaffolds. Finally, 18.4 ± 7.1 mm3(titanium-120, p = 0.015) and 18.7 ± 8.0 mm3(titanium-230, p = 0.012) of bone was formed in those defects, significantly more than in the empty defects (5.8 ± 5.1 mm3). Bending tests on the excised femurs after 12 weeks showed that the fusion strength reached 62% (titanium-120) and 45% (titanium-230) of the intact contralateral femurs, but there was no significant difference between the two scaffolds. This study showed that in addition to adequate mechanical support, porous titanium scaffolds facilitate bone formation, which results in high mechanical integrity of the treated large bone defects. Copyright

Neural network prediction of load from the morphology of trabecular bone (Article)

2013-04-01T00:00:00Z

Bone adaptation models are often solved in the forward direction, meaning that the response of bone to a given set of loads is determined by running a bone tissue adaptation model. The model is generally solved using a numerical technique such as the finite element model. Conversely, one may be interested in the loads that have resulted in a given state of bone. This is the inverse of the former problem. Even though the inverse problem has several applications, it has not received as much attention as the forward problem, partly because solving the inverse problem is more difficult. A nonlinear system identification technique is needed for solving the inverse problem. In this study, we use artificial neural networks for prediction of tissue adaptation loads from a given density distribution of trabecular bone. It is shown that the proposed method can successfully identify the loading parameters from the density distribution of the tissue. Two important challenges for all load prediction algorithms are the non-uniqueness of the solution of the inverse problem and the inaccuracies in the measurement of the morphology of the tissue. Both challenges are studied, and it is shown that the load prediction technique proposed in this paper can overcome both.

Total hip replacement but not clinical osteoarthritis can be predicted by the shape of the hip: A prospective cohort study (CHECK) (Article)

2013-04-01T00:00:00Z

Objective: To investigate the association between baseline hip shape and both clinical hip osteoarthritis (OA) and total hip replacement (THR) at 5-year follow-up. Design: Individuals from the Cohort Hip and Cohort Knee (CHECK) study, with early symptomatic OA, having standardized anteroposterior pelvic radiographs at baseline and 5-year follow-up (n = 723) were included. Hip shape on the radiographs was assessed using statistical shape modeling (SSM). Hips fulfilling the American College of Rheumatology (ACR) criteria at follow-up were classified as clinical OA. The association between each mode of shape variation and both outcome measures was calculated by Generalized Estimating Equations (GEE). Results: The included individuals comprised 575 females and 148 males (mean age 55.9 ± 5.2 years). At baseline, 8% fulfilled the ACR criteria, 76% had no radiographic hip OA [Kellgren & Lawrence (K&L) = 0] and 24% had doubtful OA (K&L = 1). At follow-up, 147 hips (10.4%) fulfilled the ACR criteria and 35 hips (2.5%) had received THR. Five shape variants (modes) at baseline associated significantly with THR within 5 years. When combined in one GEE model, these shape variants resulted in a predictive power indicated by an area under the curve of 0.81. No shape variants associated with the presence of clinical OA at follow-up. Conclusion: The shape of the hip as quantified by an SSM has a good predictive value for THR, whereas variation in shape cannot predict clinical OA. Minor shape variants may be used as a radiographic biomarker to predict the future risk of THR.

Full-field strain measurement and fracture analysis of rat femora in compression test (Article)

2013-03-18T00:00:00Z

There is a growing interest in studying the fracture behavior of bones, primarily due to the increasing societal burden of osteoporotic fractures. In addition, bone is one of the most important biological materials whose fracture behavior is not yet well understood. This is partly due to the fact that bone is a complex hierarchical material, and exhibits heterogeneous, anisotropic, and viscoelastic mechanical behavior. Understanding the fracture behavior of such a complex material requires application of a full-field strain measurement technique. Digital image correlation (DIC) is a relatively new full-field strain measurement technique that can be used for measurement of 3D surface strains during mechanical testing of different types of bones. In this study, we use the DIC technique to measure the surface strains during compression testing of two groups of rat femora. The first group of femora was harvested from young animals (12 weeks), while the second group was harvested from more mature animals (26 weeks). The surface strains are measured both in the linear range and close to the fracture. Using the measured data, we assess two strain-based fracture prediction criteria, namely equivalent strain fracture criterion and fracture limit diagram, to determine whether they can consistently predict the onset of fracture. The maximum load is measured to be 296±22 N (mean±SD) for young animals and 670±123 N for mature animals. It is shown that fracture in the vast majority of cases occurs in the area of maximum tensile strain. The equivalent strain fracture criterion predicts that the fracture occurs when the equivalent strain reaches 1.04±0.02% (average±SD) for young animals and 1.39±0.24% for mature animals. The fracture limit diagram predicts that the fracture occurs once the sum of major and minor principal surface strains reaches 0.63±0.23% for young animals and -0.63±0.30% for mature animals. Based on these numbers and consistency of the criteria with the strain values recorded at the fracture locations, it is concluded that the equivalent strain fracture criterion tends to be more consistent among the tested specimens.

Image registration improves human knee cartilage T1 mapping with delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) (Article)

2013-01-01T00:00:00Z

Objectives: To evaluate the effect of automated registration in delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) of the knee on the occurrence of movement artefacts on the T1 map and the reproducibility of region-of-interest (ROI)-based measurements. Methods: Eleven patients with early-stage knee osteoarthritis and ten healthy controls underwent dGEMRIC twice at 3 T. Controls underwent unenhanced imaging. ROIs were manually drawn on the femoral and tibial cartilage. T1 calculation was performed with and without registration of the T1-weighted images. Automated three-dimensional rigid registration was performed on the femur and tibia cartilage separately. Registration quality was evaluated using the square root Cramér-Rao lower bound (CRLBσ). Additionally, the reproducibility of dGEMRIC was assessed by comparing automated registration with manual slice-matching. Results: Automated registration of the T1-weighted images improved the T1 maps as the 90% percentile of the CRLBσwas significantly (P < 0.05) reduced with a median reduction of 55.8ms (patients) and 112.9ms (controls). Manual matching and automated registration of the re-imaged T1 map gave comparable intraclass correlation coefficients of respectively 0.89/0.90 (patients) and 0.85/0.85 (controls). Conclusions: Registration in dGEMRIC reduces movement artefacts on T1 maps and provides a good alternative to manual slice-matching in longitudinal studies. Key Points: • Quantitative MRI is increasingly used for biomedical assessment of knee articular cartilage • Image registration leads to more accurate quantification of cartilage quality and damage • Movement artefacts in delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) are reduced • Automated image registration successfully aligns baseline and follow-up dGEMRIC examinations • Reproducibility of dGEMRIC with registration is similar to that using manual slice-matching

Mesenchymal stem cells secrete factors that inhibit inflammatory processes in short-term osteoarthritic synovium and cartilage explant culture (Article)

2012-10-01T00:00:00Z

Objective: Mesenchymal stem cells (MSCs) are promising candidates for osteoarthritis (OA) therapies, although their mechanism of action remains unclear. MSCs have recently been discovered to secrete anti-inflammatory cytokines and growth factors. We studied the paracrine effects of MSCs on OA cartilage and synovial explants in vitro. Design: MSC-conditioned medium was prepared by stimulating primary human MSCs with tumour necrosis factor alpha (TNFα) and (50. ng/ml each). Human synovium and cartilage explants were cultured in MSC-conditioned medium or in control medium, containing the same amount of added TNFα and IFNγ but not incubated with MSCs. Explants were analyzed for gene expression and the production of nitric oxide (NO). The presence of the inhibitor of nuclear factor kappa B alpha (IκBa) was assessed by Western blot analysis. Results: Synovial explants exposed to MSC-conditioned medium showed decreased gene expression of interleukin-1 beta (IL-1β), matrix metalloproteinase (MMP). 1 and MMP13, while suppressor of cytokine signaling (SOCS). 1 was upregulated. In cartilage, expression of IL-1 receptor antagonist (IL-1RA) was upregulated, whereas a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS). 5 and collagen type II alpha 1 (COL2A1) were downregulated. MSC-conditioned medium reduced NO production in cartilage explants and the presence of IκBa was increased in synoviocytes and chondrocytes treated with MSC-conditioned medium. Conclusions: In an inflammatory environment, MSCs secrete factors which cause multiple anti-inflammatory effects and influence matrix turnover in synovium and cartilage explants. Thereby, the presented data encourage further study of MSCs as a treatment for joint diseases.

Estimation of 3D rotation of femur in 2D hip radiographs (Article)

2012-08-31T00:00:00Z

Femoral radiographs are affected by the degree of rotation of the femur with respect to the plane of projection. We aimed to determine the 3D rotation of the proximal femur in 2D radiographs. A 3D Statistical Appearance Model (SAM), which was built from CT images of cadaver proximal femurs (n=33) was randomly sampled to form a training set of 500 bones. Nineteen clinical CT images were collected for testing. All CT images were rotated to ±20° in 2° division around the shaft axis, ±10° around medial-lateral axis, and by simultaneous rotation of both axes (±16° and ±8° around shaft and medial-lateral axes). In each orientation, a 2D projection was recorded for generating a 2D SAM. The outcome parameters of the 2D SAM were used as input for a linear regression model and an artificial neural network to predict the rotation. The artificial neural network estimated the rotation more accurately than the linear regression. For artificial neural networks the mean errors were 4.0° and 2.0° around the shaft and medial-lateral axes, respectively. For an individual radiograph, the confidence interval of estimation was still relatively large. However, this method has high potential to differentiate the amount of rotations in two image sets.

Reproducibility of 3D delayed gadolinium enhanced MRI of cartilage (dGEMRIC) of the knee at 3.0 T in patients with early stage osteoarthritis (Article)

2012-08-13T00:00:00Z

Objectives: To assess the reproducibility of 3D delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) at 3 T in early stage knee osteoarthritis (OA) patients. Methods: In 20 patients, 3D dGEMRIC at 3 T was acquired twice within 7 days. To correct for patient motion during acquisition, all images were rigidly registered in 3D. Eight anatomical cartilage ROIs were analysed on both images of each patient. Capability of dGEMRIC to yield T1 maps that reproducibly distinguish spatial differences in cartilage quality was assessed in two ROIs within a single slice in each patient. Reproducibility was assessed using ICCs and Bland-Altman plots. Results: ICCs ranged from 0.87 to 0.95, indicating good reproducibility. T1 maps revealed reproducible spatial differences in cartilage quality (ICC 0.79). Based on the Bland-Altman plots, we defined a threshold of 95 ms to determine if a change in dGEMRIC outcome in longitudinal research was statistically significant. Conclusions: 3D knee dGEMRIC at 3 T combined with 3D image registration is a highly reproducible measure of cartilage quality in early stage OA. Therefore, dGEMRIC may be a valuable tool in the non-invasive evaluation of cartilage quality changes in longitudinal research in patients with early stage OA and focal cartilage defects. Key Points: • Delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) can assess osteoarthritis • dGEMRIC yields highly reproducible T1 values in early stage osteoarthritic patients • A threshold was established to determine significant changes in dGEMRIC outcomes • dGEMRIC can be used to evaluate cartilage quality in longitudinal research

Bone fragility and decline in stem cells in prematurely aging DNA repair deficient trichothiodystrophy mice (Article)

2012-08-01T00:00:00Z

Trichothiodystrophy (TTD) is a rare, autosomal recessive nucleotide excision repair (NER) disorder caused by mutations in components of the dual functional NER/basal transcription factor TFIIH. TTD mice, carrying a patient-based point mutation in the Xpd gene, strikingly resemble many features of the human syndrome and exhibit signs of premature aging. To examine to which extent TTD mice resemble the normal process of aging, we thoroughly investigated the bone phenotype. Here, we show that female TTD mice exhibit accelerated bone aging from 39 weeks onwards as well as lack of periosteal apposition leading to reduced bone strength. Before 39 weeks have passed, bones of wild-type and TTD mice are identical excluding a developmental defect. Albeit that bone formation is decreased, osteoblasts in TTD mice retain bone-forming capacity as in vivo PTH treatment leads to increased cortical thickness. In vitro bone marrow cell cultures showed that TTD osteoprogenitors retain the capacity to differentiate into osteoblasts. However, after 13 weeks of age TTD females show decreased bone nodule formation. No increase in bone resorption or the number of osteoclasts was detected. In conclusion, TTD mice show premature bone aging, which is preceded by a decrease in mesenchymal stem cells/osteoprogenitors and a change in systemic factors, identifying DNA damage and repair as key determinants for bone fragility by influencing osteogenesis and bone metabolism.

Pathophysiology of peri-articular bone changes in osteoarthritis (Article)

2012-08-01T00:00:00Z

Osteoarthritis (OA) is a disease that involves the entire joint, but its pathophysiology is not well described. Alterations in peri-articular bone are an integral part of the OA disease process and different aspects of bone changes have been described in different patient (sub)groups and animal models. In this review we will discuss the osteoarthritis pathophysiology from the perspective of periarticular bone changes, which can be considered at three hierarchical levels: the bone (or joint) shape, the subchondral bone architecture and its cellular and molecular phenotype. In this review we try to provide an overview of the current knowledge of peri-articular bone changes in OA and what it could possibly imply for the initiation of OA and its progression.This article is part of a Special Issue entitled "Osteoarthritis".

Systemic treatment with pulsed electromagnetic fields do not affect bone microarchitecture in osteoporotic rats (Article)

2012-07-01T00:00:00Z

Purpose: Pulsed electromagnetic fields (PEMF) are currently used in the treatment of spinal fusions and non-unions. There are indications that PEMF might also be effective in the treatment of osteoporosis. In this study we examined whether whole-body PEMF treatment affects the bone microarchitecture in an osteoporotic rat model. Methods: Twenty-week-old female rats were ovariectomised (n020). Four different PEMF treatment protocols based on previous experimental studies and based on clinically used PEMF signals were examined (2 h/day, 5 days/week). A control group did not receive PEMF. At zero, three and six weeks cancellous and cortical bone architectural changes at the proximal tibia were evaluated using in vivo microCT scanning. Results: PEMF treatment did not induce any changes in cancellous or cortical bone compared to untreated controls. Conclusions: Although previous studies have shown strong effects of PEMF in osteoporosis we were unable to demonstrate this in any of the treatment protocols. Using in vivo microCT scanning we were able to identify small bone changes in time. Subtle differences in the experimental setup might explain the differences in study outcomes in the literature. Since PEMF treatment is safe, future experimental studies on the effect of PEMF on bone can better be performed directly on humans, eliminating the potential translation issues between animals and humans. In this study we found no support for the use of PEMF in the treatment of osteoporosis.

CT arthrography of the human knee to measure cartilage quality with low radiation dose (Article)

2012-07-01T00:00:00Z

Objective: Recently, CT arthrography (CTa) was introduced as a non-destructive technique to quantitatively measure cartilage quality in human knees. This study investigated whether this is also possible using lower radiation dose CT protocols. Furthermore, we studied the ability of (lower radiation) CTa to distinguish between local sulphated glycosaminoglycan (sGAG) content differences. Design: Of ten human cadaveric knee joints, six CT scans using different radiation doses (81.33-8.13 mGy) were acquired after intra-articular ioxaglate injection. The capability of CTa to measure overall cartilage quality was determined in seven anatomical regions of interest (ROIs), using equilibrium partitioning of an ionic contrast agent using (EPIC)-microCT (μCT) as reference standard for sGAG content. To test the capability of CTa to spatially distinguish between local differences in sGAG content, we calculated the percentage of pixels incorrectly predicted as having high or low sGAG content by the different CTa protocols. Results: Low radiation dose CTa correlated well with EPIC-μCT in large ROIs (R = 0.78; R2= 0.61; P < 0.0001). CTa can also distinguish between high and low sGAG content within a single slice. However, the percentage of incorrectly predicted quality pixels increases (from 35% to 41%) when less radiation is used. This makes is hard or even impossible to differentiate between spatial differences in sGAG content in the lowest radiation scans. Conclusions: CTa acquired using low radiation exposure, comparable to a regular knee CT, is able to measure overall cartilage quality. Spatial sGAG distribution can also be determined using CTa, however for this purpose a higher radiation dose is necessary. Nevertheless, radiation dose reduction makes CTa suitable for quantitative analysis of cartilage in clinical research.

Computational load estimation of the femur (Article)

2012-06-01T00:00:00Z

The density distribution and, thus, mechanical properties of long bones such as the femur are dependent on their loading. Many bone tissue adaptation theories are proposed to describe the density distribution that results from a given set of loading parameters. It is relatively easy to measure the density distribution of long bones, for example, using Computed Tomography (CT). However, there is no easy non-invasive method for in-vivo measurement of musculoskeletal loads. It is therefore interesting to investigate whether or not it is possible to predict the musculoskeletal loads that have resulted in a certain measured density distribution using bone tissue adaptation models. An inverse problem has to be solved for that purpose. In this paper, we use Artificial Neural Networks (ANNs) to solve the associated inverse problem and estimate the loading parameters that have resulted in the CT-measured three-dimensional density distribution of a proximal femur. An ANN is trained using a dataset generated by solving the forward tissue adaptation model for a large number of loading parameters. Before training the ANN with the generated training dataset, a Gaussian noise component is added to the density distribution. This improves the robustness of the trained ANN against deviations of the measured density distribution from the predictions of the forward bone tissue adaptation model. It is shown that the proposed technique is capable of predicting loading parameters that result in a density distribution close to the measured density distribution.

Inhibiting calcineurin activity under physiologic tonicity elevates anabolic but suppresses catabolic chondrocyte markers (Article)

2012-06-01T00:00:00Z

Objective The physiologic interstitial tonicity of healthy articular cartilage (350-480 mOsm) is lowered to 280-350 mOsm in osteoarthritis (OA). This results in loss of tissue prestress, altered compressive behavior, and, thus, inferior tissue properties. This study was undertaken to determine whether physiologic tonicity in combination with the inhibition of calcineurin (Cn) activity by FK-506 has synergistic effects on human articular chondrocytes and explants in vitro. Methods OA chondrocytes and explants and non-OA chondrocytes were cultured in cytokine-free medium of 280 mOsm or 380 mOsm with or without Cn inhibition by FK-506. Chondrogenic, hypertrophic, and catabolic marker expression was evaluated at the messenger RNA (mRNA), protein, and activity levels. Results Compared to OA chondrocytes cultured at 280 mOsm, those cultured at 380 mOsm had increased expression of mRNA for chondrogenic markers (e.g., ∼13 fold for COL2; P < 0.001), and decreased COL1 expression (∼0.5 fold, P < 0.01). Inhibiting Cn activity under physiologic tonicity further enhanced the expression of anabolic markers at the mRNA level (∼50 fold for COL2; P < 0.001, ∼2 fold for AGC1; P < 0.001, and ∼3.5 fold for SOX9; P < 0.001) and at the protein level (∼6 fold for type II collagen; P < 0.001). Cn inhibition suppressed relevant collagenases as well as hypertropic and mineralization markers at the mRNA and activity levels. Expression of aggrecanase 1 and aggrecanase 2 was not influenced by tonicity or FK-506 alone, but the combination suppressed both, by ∼50% (P < 0.05) and ∼40% (P < 0.001), respectively. Generally, similar anabolic and antihypertrophic effects were observed in ex vivo cartilage explant cultures and non-OA chondrocytes. Conclusion Our findings indicate that Cn at physiologic tonicity exerts a superior effect compared to physiologic tonicity or FK-506 alone, increasing anabolic markers while suppressing hypertrophic and catabolic markers. Our data may aid in the development of improved cell-based chondral repair and OA treatment strategies. Copyright

The development of cam-type deformity in adolescent and young male soccer players (Article)

2012-05-01T00:00:00Z

Background: Cam impingement is a well-recognized cause of hip pain and might cause osteoarthritis of the hip. Clinically, cam impingement is mostly observed in young, active male patients, but only a few studies have focused on the manifestation of cam-type deformities during skeletal development.Purpose: To determine the age of onset and prevalence of cam-type deformities in young male soccer players versus controls.Study Design: Cross-sectional study; Level of evidence, 3.Methods: In this study, 89 elite preprofessional soccer players and 92 controls aged 12 to 19 years were included. In the soccer players, range of motion and impingement tests were performed. Both an anteroposterior (AP) pelvic radiograph and a frog-leg lateral radiograph of the hip were obtained according to a standardized protocol. Controls with both an AP pelvic and a frog-leg lateral radiograph and no hip disorders were obtained from radiology databases. The α angle was automatically determined in all radiographs, using a threshold value of 60°to define a cam-type deformity. Further, all radiographs were scored using a 3-point scoring system. The anterosuperior head-neck junction was classified as (1) normal, (2) flattened, or (3) having a prominence. Differences in prevalence were tested using logistic regression. Differences in range of motion were calculated using generalized estimating equations.Results: An α angle >60°was already found at the age of 12 years in some soccer players and controls. A cam-type deformity defined by α angle tended to be more prevalent in soccer players (26%) than in controls (17%; P =.31). In 13% of soccer players, a prominence was visible on radiographs and was first seen at the age of 13 years. The anterosuperior flattening (56% vs 18%, P =.0001) and prominence (13% vs 0%, P <.03) were more prevalent in soccer players than in controls.Conclusion: Cam-type deformities were recognizable and present from the age of 13 years and were more prevalent in soccer players than in their nonathletic peers. Cam-type deformity develops during adolescence and is likely to be influenced by high-impact sports practice.

Age-related skeletal dynamics and decrease in bone strength in DNA repair deficient male trichothiodystrophy mice (Article)

2012-04-10T00:00:00Z

Accumulation of DNA damage caused by oxidative stress is thought to be one of the main contributors of human tissue aging. Trichothiodystrophy (TTD) mice have a mutation in the Ercc2 DNA repair gene, resulting in accumulation of DNA damage and several features of segmental accelerated aging. We used male TTD mice to study the impact of DNA repair on bone metabolism with age. Analysis of bone parameters, measured by micro-computed tomography, displayed an earlier decrease in trabecular and cortical bone as well as a loss of periosteal apposition and a reduction in bone strength in TTD mice with age compared to wild type mice. Ex vivo analysis of bone marrow differentiation potential showed an accelerated reduction in the number of osteogenic and osteoprogenitor cells with unaltered differentiation capacity. Adipocyte differentiation was normal. Early in life, osteoclast number tended to be increased while at 78 weeks it was significantly lower in TTD mice. Our findings reveal the importance of genome stability and proper DNA repair for skeletal homeostasis with age and support the idea that accumulation of damage interferes with normal skeletal maintenance, causing reduction in the number of osteoblast precursors that are required for normal bone remodeling leading to a loss of bone structure and strength.

Periarticular Bone Changes in Osteoarthritis (Article)

2012-02-01T00:00:00Z

Osteoarthritis (OA) can be considered an organ failure with pathological aspects in cartilage, bone, ligaments, and synovium. Altogether, these tissue changes can result in pain and immobilization—a failure of the joint. It is well regarded that OA is a complex multifactorial disease with many risk factors and different etiological pathways that all lead to an apparently similar end stage. Bony changes are clearly observed in advanced OA. However, little understanding exists on the role of these changes, whether they are a consequence of cartilage damage or precede this damage and maybe play an important role in the etiological process. Even more important is the issue of pain. Radiological scores of OA do not match well with pain and mobility scores, which questions the value of these scoring systems. It seems that we do not assess the most relevant parameters. Evaluation of conventional and new radiographic parameters is still an extensive part of the OA research field. We may have overlooked certain (subtle) parameters that can be extracted from x-rays, but other imaging modalities such as MRI, CT, or SPECT might better represent OA in a clinically relevant manner.

Low-magnitude whole body vibration does not affect bone mass but does affect weight in ovariectomized rats (Article)

2012-01-01T00:00:00Z

Mechanical loading has stimulating effects on bone architecture, which can potentially be used as a therapy for osteoporosis. We investigated the skeletal changes in the tibia of ovariectomized rats during treatment with whole body vibration (WBV). Different low-magnitude WBV treatment protocols were tested in a pilot experiment using ovariectomized rats with loading schemes of 2 x 8 min/day, 5 days/ week (n = 2 rats per protocol). Bone volume and architecture were evaluated during a 10 week follow-up using in-vivo microcomputed tomography scanning. The loading protocol in which a 45 Hz sine wave was applied at 2 Hz with an acceleration of 0.5g showed an anabolic effect on bone and was therefore further analyzed in two groups of animals (n = 6 each group) with WBV starting directly after or 3 weeks after ovariectomy and compared to a control (non- WBV) group at 0, 3, 6 and 10 weeks' follow-up. In the follow-up experiment the WBV stimulus did not significantly affect trabecular volume fraction or cortical bone volume in any of the treatment groups during the 10 week follow-up. WBV did reduce weight gain that was induced as a consequence of ovariectomy. We could not demonstrate any significant effects of WBV on bone loss as a consequence of ovariectomy in rats; however, the weight gain that normally results after ovariectomy was partly prevented. Treatment with WBV was not able to prevent bone loss during induced osteoporosis.

Inhibition of Gsk3β in cartilage induces osteoarthritic features through activation of the canonical Wnt signaling pathway (Article)

2011-11-01T00:00:00Z

Objective: In the past years, the canonical Wnt/β-catenin signaling pathway has emerged as a critical regulator of cartilage development and homeostasis. In this pathway, glycogen synthase kinase-3β (GSK3β) down-regulates transduction of the canonical Wnt signal by promoting degradation of β-catenin. In this study we wanted to further investigate the role of Gsk3β in cartilage maintenance. Design: Therefore, we have treated chondrocytes ex vivo and in vivo with GIN, a selective GSK3β inhibitor. Results: In E17.5 fetal mouse metatarsals, GIN treatment resulted in loss of expression of cartilage markers and decreased chondrocyte proliferation from day 1 onward. Late (3. days) effects of GIN included cartilage matrix degradation and increased apoptosis. Prolonged (7. days) GIN treatment resulted in resorption of the metatarsal. These changes were confirmed by microarray analysis showing a decrease in expression of typical chondrocyte markers and induction of expression of proteinases involved in cartilage matrix degradation. An intra-articular injection of GIN in rat knee joints induced nuclear accumulation of β-catenin in chondrocytes 72. h later. Three intra-articular GIN injections with a 2. days interval were associated with surface fibrillation, a decrease in glycosaminoglycan expression and chondrocyte hypocellularity 6. weeks later. Conclusions: These results suggest that, by down-regulating β-catenin, Gsk3β preserves the chondrocytic phenotype, and is involved in maintenance of the cartilage extracellular matrix. Short term β-catenin up-regulation in cartilage secondary to Gsk3β inhibition may be sufficient to induce osteoarthritis-like features in vivo.

Variation in joint shape of osteoarthritic knees (Article)

2011-11-01T00:00:00Z

Objective To investigate the role of joint shape in knee osteoarthritis (OA) by determining which aspects of bone shape are different in OA knees compared with control knees. Methods Using a statistical shape model, we compared radiographs showing the shape of OA knees with radiographs showing the shape of control knees in a population of 609 women (1,218 knees) extracted from the Rotterdam Study. Furthermore, we used magnetic resonance imaging to compare the shape of knees with cartilage defects with the shape of knees without cartilage defects. Results Three statistical shape modes, referring to 3 distinct aspects of the shape of the knee, were significantly associated with the presence of radiographic OA (modes 2, 4, and 15). Mode 2 reflected the width of the femoral and tibial bones, which was increased in patients with OA. Knees with cartilage defects also had wider femoral and tibial bones compared with knees without cartilage defects. Mode 4 reflected the variation in flexion of the knee during radiography. OA knees were more extended compared with control knees. Mode 15 showed that patients with OA had an elevated lateral tibial plateau, which was associated with pain. Conclusion In women, knees with OA were wider, more extended during radiography, and had an elevated lateral tibial plateau. These results show that the shape of the knee is involved in OA, which might lead to novel imaging biomarkers to monitor or predict knee OA.

Platelet-rich plasma releasate inhibits inflammatory processes in osteoarthritic chondrocytes (Article)

2011-11-01T00:00:00Z

Background: Platelet-rich plasma (PRP) has recently been postulated as a treatment for osteoarthritis (OA). Although anabolic effects of PRP on chondrocytes are well documented, no reports are known addressing effects on cartilage degeneration. Since OA is characterized by a catabolic and inflammatory joint environment, the authors investigated whether PRP was able to counteract the effects of such an environment on human osteoarthritic chondrocytes.Hypothesis: Platelet-rich plasma inhibits inflammatory effects of interleukin-1 (IL-1) beta on human osteoarthritic chondrocytes.Study Design: Controlled laboratory study.Methods: Human osteoarthritic chondrocytes were cultured in the presence of IL-1 beta to mimic an osteoarthritic environment. Medium was supplemented with 0%, 1%, or 10% PRP releasate (PRPr, the active releasate of PRP). After 48 hours, gene expression of collagen type II alpha 1 (COL2A1), aggrecan (ACAN), a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)4, ADAMTS5, matrix metalloproteinase (MMP)13, and prostaglandin-endoperoxide synthase (PTGS)2 was analyzed. Additionally, glycosaminoglycan (GAG) content, nitric oxide (NO) production, and nuclear factor kappa B (NFB) activation were studied.Results: Platelet-rich plasma releasate diminished IL-1 beta-induced inhibition of COL2A1 and ACAN gene expression. The PRPr also reduced IL-1 beta-induced increase of ADAMTS4 and PTGS2 gene expression. ADAMTS5 gene expression and GAG content were not influenced by IL-1 beta or additional PRPr. Matrix metalloproteinase 13 gene expression and NO production were upregulated by IL-1 beta but not affected by added PRPr. Finally, PRPr reduced IL-1 beta-induced NFB activation to control levels containing no IL-1 beta.Conclusion: Platelet-rich plasma releasate diminished multiple inflammatory IL-1 beta-mediated effects on human osteoarthritic chondrocytes, including inhibition of NFB activation.Clinical Relevance: Platelet-rich plasma releasate counteracts effects of an inflammatory environment on genes regulating matrix degradation and formation in human chondrocytes. Platelet-rich plasma releasate decreases NFB activation, a major pathway involved in the pathogenesis of OA. These results encourage further study of PRP as a treatment for OA.

Quantifying osteoarthritic cartilage changes accurately using in vivo microCT arthrography in three etiologically distinct rat models (Article)

2011-11-01T00:00:00Z

In vivo microCT arthrography (μCTa) can be used to measure both quantity (volumetric) and quality (glycosaminoglycan content) of cartilage. This study investigated the accuracy of four segmentation techniques to isolate cartilage from μCTa datasets and then used the most accurate one to investigate if the μCTa method could show osteoarthritic changes in rat models during longitudinal follow-up. Volumetric measurements and glycosaminoglycan contents of patellar cartilage from in vivo μCTa-scans were compared with an ex vivo gold standard μCT-scan. Cartilage was segmented with three global thresholds and one local threshold algorithm. Comparisons were made for healthy and osteoarthritic cartilage. Next, three rat models were investigated for 24 weeks using μCTa. Osteoarthritis was induced by injection with a chemical (mono-iodoacetate), a surgical intervention (grooves applied in articular cartilage), and via exercise (strenuous running). After euthanasia, all knee joints were isolated for histology. Local thresholds accurately segmented cartilage from in vivo μCTa scans and best measured cartilage quantity and glycosaminoglycan content. Each of the three osteoarthritic rat models showed a specific pattern of osteoarthritis progression. All μCTa results were comparable to histology. In vivo μCTa is a sensitive technique for imaging cartilage degradation. Local thresholds enhanced the sensitivity of this method and will probably more accurately detect disease-modulating effects from interventional strategies. The data from rat models may serve as a reference for the time sequence of cartilage degeneration during in vivo testing of new strategies in osteoarthritis treatment. Copyright

Tendon structure's lack of relation to clinical outcome after eccentric exercises in chronic midportion Achilles tendinopathy (Article)

2011-11-01T00:00:00Z

CONTEXT: Chronic midportion Achilles tendinopathy is a common and hard-to-treat disorder characterized by degenerative changes of the tendon matrix. Ultrasonographic tissue characterization (UTC) was successfully used to quantify structural human Achilles tendon changes. This novel and reliable technique could be used in follow-up studies to relate tendon structure to symptoms. OBJECTIVE: To quantify structural tendon changes and assess clinical change in patients with tendinopathy. DESIGN: Prospective observational study. SETTING: Orthopedic department in a university medical center. PATIENTS: 23 patients with chronic midportion Achilles tendinopathy. INTERVENTION: The patients performed a 16-wk home-based eccentric exercise program. An experienced researcher performed the ultrasonographic data collection with the UTC procedure. These data were assessed by a blinded observer. The severity of symptoms was established with the validated Victorian Institute of Sport Assessment-Achilles (VISA-A) questionnaire. MAIN OUTCOME MEASURES: UTC was performed to quantify tendon structure through measuring the proportion of 4 echo types. Echo types I and II represent more or less organized tendon bundles, and echo types III and IV represent disintegrated tendon structure. On the VISA-A, the total possible score is divided by 100 for a percentage score, with a perfect score of 100. Follow-up was at 2, 8, 16, and 24 wk. RESULTS: The mean percentage of echo types I and II changed by 0.3% after 24 wk (P = .92, 95% CI -5.8 to 5.3). The mean VISA-A score increased slightly but significantly by 11.3 points after 24 wk (P = .01, 95% CI 2.6-20.0). An increased VISA-A score was not correlated with an increased percentage of echo types I and II (P = .94, r = -.02), and the baseline percentage of echo types I and II did not correlate with an increased VISA-A score (P = .74, r = .07). CONCLUSIONS: There is no short-term increase in organized tendon structure after eccentric exercises. Tendon structure is not related to symptom severity and cannot be used as a predictor of clinical outcome.

Clinically applied CT arthrography to measure the sulphated glycosaminoglycan content of cartilage (Article)

2011-10-01T00:00:00Z

Objective: Similar to delayed gadolinium enhanced MRI of cartilage, it might be possible to image cartilage quality using CT arthrography (CTa). This study assessed the potential of CTa as a clinically applicable tool to evaluate cartilage quality in terms of sulphated glycosaminoglycan content (sGAG) and structural composition of the extra-cellular matrix (ECM). Methods: Eleven human cadaveric knee joints were scanned on a clinical CT scanner. Of each knee joint, a regular non-contrast CT (ncCT) and an ioxaglate injected CTa scan were performed. Mean X-ray attenuation of both scans was compared to identify contrast influx in seven anatomical regions of interest (ROIs). All ROIs were rescanned with contrast-enhanced μCT, which served as the reference standard for sGAG content. Mean X-ray attenuation from both ncCT and CTa were correlated with μCT results and analyzed with linear regression. Additionally, residual values from the linear fit between ncCT and μCT were used as a covariate measure to identify the influence of structural composition of cartilage ECM on contrast diffusion into cartilage in CTa scans. Results: CTa resulted in higher X-ray attenuation in cartilage compared to ncCT scans for all anatomical regions. Furthermore, CTa correlated excellent with reference μCT values (sGAG) (R=0.86; R2=0.73; P<0.0001). When corrected for structural composition of cartilage ECM, this correlation improved substantially (R=0.95; R2=0.90; P<0.0001). Conclusions: Contrast diffusion into articular cartilage detected with CTa correlates with sGAG content and to a lesser extent with structural composition of cartilage ECM. CTa may be clinically applicable to quantitatively measure the quality of articular cartilage.

One-year follow-up of platelet-rich plasma treatment in chronic achilles tendinopathy: A double-blind randomized placebo-controlled trial (Article)

2011-08-01T00:00:00Z

Background: Achilles tendinopathy is a common disease among both athletes and in the general population in which the use of platelet-rich plasma has recently been increasing. Good evidence for the use of this autologous product in tendinopathy is limited, and data on longer-term results are lacking. Purpose: To study the effects of a platelet-rich plasma injection in patients with chronic midportion Achilles tendinopathy at 1-year follow-up. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: Fifty-four patients, aged 18 to 70 years, with chronic tendinopathy 2 to 7 cm proximal to the Achilles tendon insertion were randomized to receive either a blinded injection containing platelet-rich plasma or saline (placebo group) in addition to an eccentric training program. The main outcome was the validated Victorian Institute of Sports Assessment-Achilles score. Patient satisfaction was recorded and ultrasound examination performed at baseline and follow-up. Results: The mean Victorian Institute of Sports Assessment-Achilles score improved in both the platelet-rich plasma group and the placebo group after 1 year. There was no significant difference in increase between both groups (adjusted between-group difference, 5.5; 95% confidence interval,-4.9 to 15.8, P = .292). In both groups, 59% of the patients were satisfied with the received treatment. Ultrasonographic tendon structure improved significantly in both groups but was not significantly different between groups (adjusted between-group difference, 1.2%; 95% confidence interval,-4.1 to 6.6, P = .647). Conclusion: This randomized controlled trial showed no clinical and ultrasonographic superiority of platelet-rich plasma injection over a placebo injection in chronic Achilles tendinopathy at 1 year combined with an eccentric training program.

Bone remodelling around a cementless glenoid component (Article)

2011-07-01T00:00:00Z

Post-operative change in the mechanical loading of bone may trigger its (mechanically induced) adaptation and hamper the mechanical stability of prostheses. This is especially important in cementless components, where the final fixation is achieved by the bone itself. The aim of this study is, first, to gain insight into the bone remodelling process around a cementless glenoid component, and second, to compare the possible bone adaptation when the implant is assumed to be fully bonded (best case scenario) or completely loose (worst case scenario). 3D finite element models of a scapula with and without a cementless glenoid component were created. 3D geometry of the scapula, material properties, and several physiological loading conditions were acquired from or estimated for a specific cadaver. Update of the bone density after implantation was done according to a node-based bone remodelling scheme. Strain energy density for different loading conditions was evaluated, weighted according to their frequencies in activities of daily life and used as a mechanical stimulus for bone adaptation. The average bone density in the glenoid increased after implantation. However, local bone resorption was significant in some regions next to the bone-implant interface, regardless of the interface condition (bonded or loose). The amount of bone resorption was determined by the condition imposed to the interface, being slightly larger when the interface was loose. An ideal screw, e.g. in which material fatigue was not considered, was enough to keep the interface micromotions small and constant during the entire bone adaptation simulation.

Osteoarthritis Susceptibility Genes Influence the Association Between Hip Morphology and Osteoarthritis (Article)

2011-05-01T00:00:00Z

Abstract. OBJECTIVE: The identified osteoarthritis (OA) susceptibility genes are mainly active in skeletal development and could thus affect joint geometry. Because nonoptimal joint geometry is a risk factor for the development of OA, we investigated if and how the path that leads from nonoptimal joint geometry to OA of the hip is influenced by these genes. METHODS: The shape of the hips of subjects in the Genetics, Osteoarthritis and Progression Study, consisting of sibling pairs with symptomatic OA at multiple joint locations, was quantified by applying a statistical shape model to radiographs. Shape aspects (modes) were correlated to OA characteristics. We then tested for the association of shape modes with OA susceptibility single-nucleotide polymorphisms (SNPs) of GDF5, FRZB, and DIO2. RESULTS: Four of 23 shape modes (mode 1, mode 17, mode 18, and mode 21) were strongly associated with OA characteristics. We observed a significant interaction between carrier status of DIO2 rs12885300 and hip OA characteristics for mode 1 (P = 0.005). This indicates that this specific aspect of hip shape correlates with OA characteristics only in carriers of the susceptibility allele. CONCLUSION: Our results suggest that it is more likely that the rs12885300 SNP of DIO2 increases the vulnerability of cartilage to nonoptimal bone shapes rather than directly influencing the formation of these shapes.

No effects of PRP on ultrasonographic tendon structure and neovascularisation in chronic midportion Achilles tendinopathy (Article)

2011-04-01T00:00:00Z

Abstract. OBJECTIVE: To assess whether a platelet-rich plasma (PRP) injection leads to an enhanced tendon structure and neovascularisation, measured with ultrasonographic techniques, in chronic midportion Achilles tendinopathy. DESIGN: Double-blind, randomised, placebo-controlled clinical trial. SETTING: Sports medical department of The Hague medical centre. PATIENTS: 54 patients with chronic midportion Achilles tendinopathy were included. INTERVENTIONS: Patients were randomised to eccentric exercise therapy with either a PRP injection (PRP group) or a saline injection (placebo group). MAIN OUTCOME MEASUREMENTS: Tendon structure was evaluated by ultrasonographic tissue characterisation, a novel technique which quantifies tendon structure into four echo-types: echo-types I+II represent organised tendon bundles, whereas echo-types III+IV represent a disorganised tendon structure. Colour Doppler ultrasonography was used to measure the degree of neovascularisation. Follow-up was at 6, 12 and 24 weeks. RESULTS: A significant improvement in echo-types I+II was found after 24 weeks within both the PRP group (n=27) and the placebo group (n=27), but there was no significant between-group difference (95% CI -1.6 to 7.8, p=0.169). After 6 weeks, the neovascularisation score increased within the PRP group (p=0.001) and the placebo group (p=0.002), but there was no significant between-group difference in change in neovascularisation score at any point in time. CONCLUSION: Injecting PRP for the treatment of chronic midportion Achilles tendinopathy does not contribute to an increased tendon structure or alter the degree of neovascularisation, compared with placebo.

Femoral Component Neck Fracture After Failed Hip Resurfacing Arthroplasty (Article)

2011-03-11T00:00:00Z

Abstract: Failure on the femoral side after third-generation metal-on-metal hip resurfacing arthroplasty is suggested to be easily treated with conversion to conventional total hip arthroplasty. Clinical results of conversion for failed hip resurfacing arthroplasty with the use of primary femoral implants confirmed this for a short-term follow-up. We present a case of the occurrence of a stemmed femoral implant neck fracture in a patient who was earlier treated for a failed hip resurfacing. We advise to consider acetabular revision in case of (suspected) acetabular metal damage and to use a stem component with a relative large neck diameter.

Clinically Translatable Cell Tracking and Quantification by MRI in Cartilage Repair Using Superparamagnetic Iron Oxides (Article)

2011-03-02T00:00:00Z

Abstract BACKGROUND: Articular cartilage has very limited intrinsic regenerative capacity, making cell-based therapy a tempting approach for cartilage repair. Cell tracking can be a major step towards unraveling and improving the repair process of these therapies. We studied superparamagnetic iron oxides (SPIO) for labeling human bone marrow-derived mesenchymal stem cells (hBMSCs) regarding effectivity, cell viability, long term metabolic cell activity, chondrogenic differentiation and hBMSC secretion profile. We additionally examined the capacity of synovial cells to endocytose SPIO from dead, labeled cells, together with the use of magnetic resonance imaging (MRI) for intra-articular visualization and quantification of SPIO labeled cells. METHODOLOGY/PRINICIPAL FINDINGS: Efficacy and various safety aspects of SPIO cell labeling were determined using appropriate assays. Synovial SPIO re-uptake was investigated in vitro by co-labeling cells with SPIO and green fluorescent protein (GFP). MRI experiments were performed on a clinical 3.0T MRI scanner. Two cell-based cartilage repair techniques were mimicked for evaluating MRI traceability of labeled cells: intra-articular cell injection and cell implantation in cartilage defects. Cells were applied ex vivo or in vitro in an intra-articular environment and immediately scanned. SPIO labeling was effective and did not impair any of the studied safety aspects, including hBMSC secretion profile. SPIO from dead, labeled cells could be taken up by synovial cells. Both injected and implanted SPIO-labeled cells could accurately be visualized by MRI in a clinically relevant sized joint model using clinically applied cell doses. Finally, we quantified the amount of labeled cells seeded in cartilage defects using MR-based relaxometry. CONCLUSIONS: SPIO labeling appears to be safe without influencing cell behavior. SPIO labeled cells can be visualized in an intra-articular environment and quantified when seeded in cartilage defects.

Microstructure and biomechanical characteristics of bone substitutes for trauma and orthopaedic surgery (Article)

2011-02-04T00:00:00Z

Abstract. BACKGROUND: Many (artificial) bone substitute materials are currently available for use in orthopaedic trauma surgery. Objective data on their biological and biomechanical characteristics, which determine their clinical application, is mostly lacking. The aim of this study was to investigate structural and in vitro mechanical properties of nine bone substitute cements registered for use in orthopaedic trauma surgery in the Netherlands. METHODS: Seven calcium phosphate cements (BoneSource®, Calcibon®, ChronOS®, Eurobone®, HydroSet™, Norian SRS®, and Ostim®), one calcium sulphate cement (MIIG® X3), and one bioactive glass cement (Cortoss®) were tested. Structural characteristics were measured by micro-CT scanning. Compression strength and stiffness were determined following unconfined compression tests. RESULTS: Each bone substitute had unique characteristics. Mean total porosity ranged from 53% (Ostim®) to 0.5% (Norian SRS®). Mean pore size exceeded 100 μm only in Eurobone® and Cortoss® (162.2 ± 107.1 μm and 148.4 ± 70.6 μm, respectively). However, 230 μm pores were found in Calcibon®, Norian SRS®, HydroSet™, and MIIG® X3. Connectivity density ranged from 27/cm3 for HydroSet™ to 0.03/cm3 for Calcibon®. The ultimate compression strength was highest in Cortoss® (47.32 MPa) and lowest in Ostim® (0.24 MPa). Young's Modulus was highest in Calcibon® (790 MPa) and lowest in Ostim® (6 MPa). CONCLUSIONS: The bone substitutes tested display a wide range in structural properties and compression strength, indicating that they will be suitable for different clinical indications. The data outlined here will help surgeons to select the most suitable products currently available for specific clinical indications.

Osteoarthritis induction leads to early and temporal subchondral plate porosity in the tibial plateau of mice: an in vivo micro CT study. (Article)

2011-02-01T00:00:00Z

Abstract: In osteoarthritis (OA) changes occur both in cartilage and subchondral bone. The subchondral bone plate facilitates normal crosstalk between articular cartilage and trabecular subchondral bone, and adaptive changes in the plate due to OA may therefore disturb crosstalk homeostasis. To investigate these changes over time we examined the cartilage-subchondral bone interface using a combined approach of histology and in vivo micro CT. Male C57Bl/6 mice (n=8), aged 16 weeks, received intra-articular injections with collagenase in one joint to induce instability-related OA and saline into the contralateral knee joint (controls). At 2, 4, 6, 10 and 14 weeks post-injection, changes in the tibial subchondral bone plate and subchondral trabeculae were analyzed. At two weeks post-injection, collagenase injected joints had significantly more cartilage damage and osteophytosis than control joints. Osteoclast activity directly underneath the subchondral bone plate was significantly elevated (Oc.S./BS controls: 7.60± 0.81%; OA: 11.07± 0.79%), causing the plate to become thinner and creating a large increase in subchondral bone plate porosity (cumulative porosity volume controls: 0.05e-3 ± 0.04e-3 mm(3) ; OA: 2.52e-3 ± 0.69e-3 mm(3) ). At four weeks post-injection, the previously formed perforations disappeared, coinciding with a significant rise in osteoblast activity in the subchondral trabecular bone (bone formation rate controls: 0.30± 0.03, OA: 0.62± 0.13 μm(2) /μm(3) *day). The current study provides for the first time quantitative longitudinal data on the dynamic changes in the subchondral bone plate after OA induction. The development of plate perforations may enhance mutual interaction between subchondral trabeculae, bone marrow cells and the articular cartilage in OA.

Unfocused Extracorporeal Shock Waves Induce Anabolic Effects in Rat Bone (Article)

2011-01-05T00:00:00Z

Abstract. BACKGROUND: Extracorporeal shock waves are known to stimulate the differentiation of mesenchymal stem cells toward osteoprogenitors and induce the expression of osteogenic-related growth hormones. The aim of this study was to investigate if and how extracorporeal shock waves affected new bone formation, bone microarchitecture, and the mechanical properties of bone in a healthy rat model, in order to evaluate whether extracorporeal shock wave therapy might be a potential treatment for osteoporosis. METHODS: Thirteen rats received 1000 electrohydraulically generated unfocused extracorporeal shock waves to the right tibia. The contralateral, left tibia was not treated and served as a control. At two, seven, twenty-one, and forty-nine days after administration of the shock waves, in vivo single-photon-emission computed tomography (SPECT) scanning was performed to measure new bone formation on the basis of uptake of technetium-labeled methylene diphosphonate ((99m)Tc-MDP) (n = 6). Prior to and forty-nine days after the extracorporeal shock wave therapy, micro-computed tomography (micro-CT) scans were made to examine the architectural bone changes. In addition, mechanical testing, microcrack, and histological analyses were performed. RESULTS: Extracorporeal shock waves induced a strong increase in (99m)Tc-MDP uptake in the treated tibia compared with the uptake in the untreated, control tibia. Micro-CT analysis showed that extracorporeal shock waves stimulated increases in both trabecular and cortical volume, which resulted in higher bone stiffness compared with that of the control tibiae. Histological analysis showed intramedullary soft-tissue damage and de novo bone with active osteoblasts and osteoid in the bone marrow of the legs treated with extracorporeal shock waves. Microcrack analysis showed no differences between the treated and control legs. CONCLUSIONS: This study shows that a single treatment with extracorporeal shock waves induces anabolic effects in both cancellous and cortical bone, leading to improved biomechanical properties. Furthermore, treatment with extracorporeal shock waves results in transient damage to the bone marrow, which might be related to the anabolic effects. After further examination and optimization, unfocused extracorporeal shock waves might enable local treatment of skeletal sites susceptible to fracture.

Oestrogen is important for maintenance of cartilage and subchondral bone in a murine model of knee osteoarthritis (Article)

2010-10-05T00:00:00Z

Introduction: Oestrogen depletion may influence onset and/or progression of osteoarthritis. We investigated in an ovariectomized mouse model the impact of oestrogen loss and oestrogen supplementation on articular cartilage and subchondral bone in tibia and patella, and assessed bone changes in osteoarthritis development.Methods: C3H/HeJ mice were divided into four groups: sham-operated, oestrogen depletion by ovariectomy (OVX), OVX with estradiol supplementation (OVX+E) and OVX with bisphosphonate (OVX+BP). Each mouse had one knee injected with low-dose iodoacetate (IA), and the contralateral knee was injected with saline. Cartilage was analysed histologically 12 weeks postsurgery; bone changes were monitored over time using in vivo micro-computed tomography.Results: In tibiae, OVX alone failed to induce cartilage damage, but OVX and IA combination significantly induced cartilage damage. In patellae, OVX alone induced significant cartilage damage, which was enhanced by IA. In both tibiae and patellae, OVX in combination with IA significantly decreased subchondral cortical thickness in an additive manner. OVX+E and OVX+BP inhibited tibial and patellar subchondral cortical thinning, inhibited patellar and tended to diminish tibial cartilage damage. In patellae, IA interacted with BP, leading to increased subchondral cortical and trabecular bone.Conclusions: This study demonstrates the significance of oestrogen for articular cartilage and subchondral bone and maintenance of healthy joints, supporting an etiological role for altered oestrogen signaling in osteoarthritis either by directly affecting cartilage or increasing susceptibility for an osteoarthritis trigger. The data strongly support the concept of involvement of subchondral bone plate in osteoarthritis.

Analysis of osteoarthritis in a mouse model of the progeroid human DNA repair syndrome trichothiodystrophy (Article)

2010-09-07T00:00:00Z

The increasing average age in developed societies is paralleled by an increase in the prevalence of many age-related diseases such as osteoarthritis (OA), which is characterized by deformation of the joint due to cartilage damage and increased turnover of subchondral bone. Consequently, deficiency in DNA repair, often associated with premature aging, may lead to increased pathology of these two tissues. To examine this possibility, we analyzed the bone and cartilage phenotype of male and female knee joints derived from 52- to 104-week-old WT C57Bl/6 and trichothiodystrophy (TTD) mice, who carry a defect in the nucleotide excision repair pathway and display many features of premature aging. Using micro-CT, we found bone loss in all groups of 104-week-old compared to 52-week-old mice. Cartilage damage was mild to moderate in all mice. Surprisingly, female TTD mice had less cartilage damage, proteoglycan depletion, and osteophytosis compared to WT controls. OA severity in males did not significantly differ between genotypes, although TTD males had less osteophytosis. These results indicate that in premature aging TTD mice age-related changes in cartilage were not more severe compared to WT mice, in striking contrast with bone and many other tissues. This segmental aging character may be explained by a difference in vasculature and thereby oxygen load in cartilage and bone. Alternatively, a difference in impact of an anti-aging response, previously found to be triggered by accumulation of DNA damage, might help explain why female mice were protected from cartilage damage. These findings underline the exceptional segmental nature of progeroid conditions and provide an explanation for pro- and anti-aging features occurring in the same individual.

Stimulation of osteogenic differentiation in human osteoprogenitor cells by pulsed electromagnetic fields: An in vitro study (Article)

2010-08-26T00:00:00Z

Background: Although pulsed electromagnetic field (PEMF) stimulation may be clinically beneficial during fracture healing and for a wide range of bone disorders, there is still debate on its working mechanism. Mesenchymal stem cells are likely mediators facilitating the observed clinical effects of PEMF. Here, we performed in vitro experiments to investigate the effect of PEMF stimulation on human bone marrow-derived stromal cell (BMSC) metabolism and, specifically, whether PEMF can stimulate their osteogenic differentiation. Methods: BMSCs derived from four different donors were cultured in osteogenic medium, with the PEMF treated group being continuously exposed to a 15 Hz, 1 Gauss EM field, consisting of 5-millisecond bursts with 5-microsecond pulses. On culture day 1, 5, 9, and 14, cells were collected for biochemical analysis (DNA amount, alkaline phosphatase activity, calcium deposition), expression of various osteoblast-relevant genes and activation of extracellular signal-regulated kinase (ERK) signaling. Differences between treated and control groups were analyzed using the Wilcoxon signed rank test, and considered significant when p < 0.05. Results: Biochemical analysis revealed significant, differentiation stage-dependent, PEMF-induced differences: PEMF increased mineralization at day 9 and 14, without altering alkaline phosphatase activity. Cell proliferation, as measured by DNA amounts, was not affected by PEMF until day 14. Here, DNA content stagnated in PEMF treated group, resulting in less DNA compared to control. Quantitative RT-PCR revealed that during early culture, up to day 9, PEMF treatment increased mRNA levels of bone morphogenetic protein 2, transforming growth factor-beta 1, osteoprotegerin, matrix metalloproteinase-1 and-3, osteocalcin, and bone sialoprotein. In contrast, receptor activator of NF-B ligand expression was primarily stimulated on day 14. ERK1/2 phosphorylation was not affected by PEMF stimulation. Conclusions: PEMF exposure of differentiating human BMSCs enhanced mineralization and seemed to induce differentiation at the expense of proliferation. The osteogenic stimulus of PEMF was confirmed by the up-regulation of several osteogenic marker genes in the PEMF treated group, which preceded the deposition of mineral itself. These findings indicate that PEMF can directly stimulate osteoprogenitor cells towards osteogenic differentiation. This supports the theory that PEMF treatment may recruit these cells to facilitate an osteogenic response in vivo. © 2010 Jansen et al; licensee BioMed Central Ltd.

Similarities and discrepancies in subchondral bone structure in two differently induced canine models of osteoarthritis (Article)

2010-07-01T00:00:00Z

In osteoarthritis (OA), cartilage degradation is accompanied by subchondral bone changes. The pathogenesis and physiology of bone changes in OA are still unclear. The changes in subchondral bone architecture and cartilage damage were compared in differently induced experimental models of OA. Experimental OA was induced bilaterally by anterior cruciate ligament transection (ACLT) or by cartilage trauma (Groove model); bilateral sham surgery served as control. Lysylpyridinoline (LP, bone resorption) and C-telopeptide of type II collagen (CTX-II, cartilage breakdown) were measured over time. At 20 weeks after surgery, the subchondral cortical plate and trabecular bone of the tibia were analyzed by micro-computed tomography (μCT) and cartilage degeneration was analyzed histologically and biochemically. In both models, cartilage degeneration and cortical subchondral plate thinning were present. CTXII levels were elevated over time in both models. Subchondral trabecular bone changes were observed only in the ACLT model, not in the Groove model. Correspondingly, LP levels were elevated over time in the ACLT model and not in the Groove model. Interestingly, the trabecular bone changes in the ACLT model were extended to the metaphyseal area. The early decrease in plate thickness, present in both models, as was cartilage damage, suggests that plate thinning is a phenomenon that is intrinsic to the process of OA independent of the cause/induction of OA. On the other hand, trabecular changes in subchondral and metaphyseal bone are not part of a common pathway of OA development and may be induced biomechanically in the destabilized and less loaded ACLT joint.

A statistical model of shape and density of the proximal femur in relation to radiological and clinical OA of the hip (Article)

2010-06-01T00:00:00Z

Objective: Common radiological measures of osteoarthritis (OA) relate poorly to symptoms as experienced by patients. We created a statistical model of shape and density to see if Dual Energy X-ray (DXA) images of the hip contain symptom-related information that is not captured by common radiological measures. Methods: DXA images of the hip were made in a prospective study of patients that met the American College of Rheumatology (ACR) criteria for hip OA. From the DXA scans, we constructed a statistical model of the appearance (shape combined with density) of the proximal femur of left and right side. The model yields a number of independent descriptors of the appearance (modes) which we related to various measures of radiological and clinical OA. These outcome measures were defined using Joint Space Width (JSW), Kellgren and Lawrence (KeL) scores, Visual Analogue Scale (VAS) and Western Ontario MacMaster Universities (WOMAC) pain scores and a self-reported global assessment score. Results: Various modes showed significant relations with measures of OA. Interestingly, the modes that related well with radiological OA did not relate to clinical OA and vice-versa. Moreover, the modes were predictors of status and progression of clinical OA, independent from JSW and KeL. Conclusion: Statistical modeling of the appearance captures the patterns of variation in projected femoral morphology as visible on DXA images. We showed that these descriptors of subtle aspects of shape and density of the hip contain information about clinical status which common radiological measures do not. The presented results warrant further careful study of the method as a monitoring tool in clinical trials.

Physiological tonicity improves human chondrogenic marker expression through nuclear factor of activated T-cells 5 in vitro (Article)

2010-05-01T00:00:00Z

Abstract Introduction: Chondrocytes experience a hypertonic environment compared to plasma (280 mOsm) due to the high fixed negative charge density of cartilage. Standard isolation of chondrocytes removes their hypertonic matrix, exposing them to non-physiological conditions. During in-vitro expansion, chondrocytes quickly lose their specialized phenotype, making them inappropriate for cell-based regenerative strategies. We aimed to elucidate the effects of tonicity during isolation and in-vitro expansion on chondrocyte phenotype. Methods: Human articular chondrocytes were isolated and subsequently expanded at control tonicity (280 mOsm) or at moderately elevated, physiological, tonicity (380 mOsm). The effects of physiological tonicity on chondrocyte proliferation and chondrogenic marker expression were evaluated. The role of Tonicity-responsive Enhancer Binding Protein (TonEBP/NFAT5) in response to physiological tonicity was investigated using nuclear factor of activated T-cells 5 (NFAT5) RNA interference. Results: Moderately elevated, physiological, tonicity (380 mOsm) did not affect chondrocyte proliferation, while higher tonicities inhibited proliferation and diminished cell viability. Physiological tonicity improved expression of chondrogenic markers and NFAT5 and its target genes, while suppressing dedifferentiation marker collagen type I and improving type II/type I expression ratios >100-fold. Effects of physiological tonicity were similar in osteoarthritic and ‘normal’ (non-osteoarthritic) chondrocytes, indicating a disease-independent mechanism. NFAT5 RNA interference abolished tonicity-mediated effects and revealed that NFAT5 positively regulates collagen type II expression, while suppressing type I. Conclusions: Physiological tonicity provides a simple, yet effective, means to improve phenotypical characteristics during cytokine-free isolation and in-vitro expansion of human articular chondrocytes. Our findings will lead to the development of improved cell-based repair strategies for chondral lesions and provides important insights into mechanisms underlying osteoarthritic progression.

Estrogen Modulates Iodoacetate-Induced Gene Expression in Bovine Cartilage Explants (Article)

2010-05-01T00:00:00Z

Abstract Estrogen loss may be involved in onset or progression of osteoarthritis. Estrogen receptors are present in chondrocytes, thus estrogen may exert effects directly on cartilage. However, studies on direct estrogen effects on cartilage are limited. We investigated, in an in vitro cartilage explant model, whether estrogen prevents damage or stimulates repair after damage induced by addition of iodoacetate (IA), as an experimental model for osteoarthritis. We used healthy bovine cartilage explants. Prevention experiment: Explants precultured with/without estradiol (E) for 3 days were cultured with IA for 4 h on day 0, and subsequently cultured as in preculture: with/without E. Explants were harvested at day 2 for gene expression analysis. Repair experiment: At day 0, explants were cultured with IA for 4 h on day 0, and subsequently cultured without E or with E. Explants were harvested at days 2, 10, and 14 for gene expression analysis. IA transiently downregulated most genes tested, whereas vascular endothelial growth factor (VEGF) was upregulated on day 2. On day 14, transforming growth factor beta (TGFB)1 and TGFB3 were upregulated, and matrix metalloproteinase (MMP)13 and VEGF downregulated. Estradiol affected gene expression of aggrecan (AGC)1, MMP2, MMP14, tissue inhibitor of metalloproteinase (TIMP)2, TGFB2, and TGFB3. Prevention experiment: Estradiol did not significantly affect IA-induced changes in gene expression (no significant interaction). Repair experiment: Estradiol affected IA-induced changes in expression of collagen (COL)2, MMP2, MMP3, MMP13, MMP14, TIMP2, TGFB2, TGFB3, and VEGF. Estradiol affects expression of anabolic and catabolic genes in bovine cartilage explants and modulates the effects of IA. These effects of estradiol may be beneficial for cartilage maintenance and repair.

In early OA, thinning of the subchondral plate is directly related to cartilage damage: results from a canine ACLT-meniscectomy model (Article)

2010-05-01T00:00:00Z

Abstract OBJECTIVE: The pathogenesis of osteoarthritis (OA) includes cartilage degeneration, synovial inflammation, and bone changes. Slowly, the sequence and inter-relationship of these features is becoming clearer. Early models of OA suggest thinning of the subchondral plate in addition to trabecular bone changes. In the present study subchondral bone changes were studied in the canine anterior cruciate ligament transection (ACLT)-meniscectomy model. This model is characterized by intra-joint variability with respect to cartilage damage (predominantly medial) and loading (lateral unloading due to a shifted axis). METHODS: In 13 Labrador dogs, OA was induced by transection of the anterior cruciate ligament and removal of the medial meniscus. Twelve weeks later, cartilage integrity was evaluated histologically using the modified Mankin score (0-11), and proteoglycan content was determined by Alcian Blue assay. Bone architecture of the tibia was quantified by micro-CT. RESULTS: Cartilage damage was severe in the medial compartment (Mankin score +3.5, glycosaminoglycan (GAG) content -28%) and mild in the lateral compartment (Mankin score +1.6, GAG content -15%). Thinning and porosity of the subchondral plate were only present on the medial side (-21%, +87%, respectively). Interestingly, changes in trabecular bone structure did almost not occur in the medial compartment (volume fraction -7%) but were clear in the lateral compartment (-20%). CONCLUSION: Thinning of the subchondral plate is a localized phenomenon related to cartilage degeneration while trabecular bone changes are related to mechanical (un)loading. The different mechanisms responsible for bone changes in OA should be taken in account when designing and interpreting studies interfering with bone turnover in the treatment of OA.

Effects of individual control of pH and hypoxia in chondrocyte culture (Article)

2010-04-01T00:00:00Z

Abstract Effects of oxygen tension (pO(2)) and pH on gene and protein expression and metabolic activity of human chondrocytes were independently assessed. Chondrocytes were cultured under a range of pH (6.4-7.4) and different pO(2) (5 and 20%) during 5 days in a bioreactor. Effects on gene expression, DNA content, protein expression, and metabolic activity were determined. Linear regression analysis showed that gene expression of type I collagen (COL1), SOX9, and VEGF is significantly lower at acidic pH, while expression of aggrecan, type II collagen, and HIF1A is pH-independent. Higher protein levels of VEGF were found under low pO(2). Acidic pH severely lowered VEGF release into medium, glucose consumption, and lactate production. Extracellular pH proved to more potently influence cell function than oxygen tension, the latter showing down-regulation of COL1 gene expression and up-regulation of VEGF protein under hypoxia. Hypoxic culture inhibits COL1 mRNA expression pH-dependently, while expression of SOX9 is largely hypoxia independent, but pH dependent. Expression of HIF1A and VEGF revealed divergent pH dependencies. Subtle fluctuations in extracellular pH and oxygen tension clearly influence chondrocyte metabolism and marker expression. Sophisticated pH and oxygen control not only allows study of (patho)physiological changes, but also opens new venues in cartilage tissue engineering.

Stretch-Induced Inhibition of Wnt/b-Catenin Signaling in Mineralizing Osteoblasts (Article)

2010-03-01T00:00:00Z

Wnt signaling is important for bone formation and osteoblastic differentiation. Recent findings indicate a stimulating role of Wnt signaling in bone mechanotransduction. However, negative effects of Wnt signaling on osteoblast differentiation and mineralization have been described as well. We conducted in vitro stretch experiments using human pre-osteoblasts to study short- and long-term effects of mechanical loading on Wnt/beta-catenin signaling. As the extracellular regulated kinase (ERK) pathway is known to be involved in mechanotransduction in osteoblasts, we also evaluated its role in Wnt/beta-catenin signaling. Stretch experiments up to 21 days (using stretch episodes of 15 min, alternated with 90 min rest) resulted in higher mineralization compared to static control cultures. We found that 15 min of stretch initially increased nuclear beta-catenin, but ultimately resulted in significant decrease at 12 and 40 h after stretch. Downregulation of Wnt-responsive element activity 16 h after stretch, using a luciferase construct, further supported these findings. The presence of the ERK inhibitor U0126 did not alter the stretch-induced decrease of beta-catenin levels. Our data indicate a biphasic effect of mechanical loading on beta-catenin in mineralizing human differentiating osteoblasts, which is independent of the ERK pathway. The osteogenic potential of our loading regime was confirmed by an increase in osteogenic differentiation markers such as alkaline phosphatase activity and calcium deposition after 3 weeks of culture. We conjecture that the biphasic aspect of Wnt/beta-catenin signaling with a strong decrease up to 40 h after the stretch induction, is important for the anabolic effects of mechanical stretch on bone.

Flight feather shaft structure of two warbler species with different moult schedules: A study using high-resolution X-ray imaging (Article)

2010-02-01T00:00:00Z

Plumage constitutes a significant component of the somatic investment of birds. A detailed investigation of feathers and moult can help to uncover trade-offs involved in somatic investment decisions, the sources of some of the costs birds have to pay and the potential fitness consequences. We used micro-computed tomography imaging to study the second moment of area, a structural parameter that is one determinant of bending stiffness and the cortex volume of flight feather shafts of two sister taxa, the willow warbler Phylloscopus trochilus, a migratory species with two annual moults, and the chiffchaff Phylloscopus collybita, a migrant with one annual post-nuptial moult. Juvenile and adult willow warbler and chiffchaff feathers, all grown on the breeding grounds, are structurally very similar to each other. Willow warbler feathers grown during moult on the wintering grounds, however, have a significantly higher second moment of area and a significantly larger cortex volume than all the other feather types. We discuss the possibility that the seasonal variability of willow warbler feathers may be an adaptive structural reflection of a moult-migration strategy that has allowed this species to occupy large breeding and wintering ranges. © 2009 The Authors. Journal compilation.

Platelet-rich plasma injection for chronic Achilles tendinopathy: A randomized controlled trial (Article)

2010-01-13T00:00:00Z

Context: Tendon disorders comprise 30% to 50% of all activity-related injuries; chronic degenerative tendon disorders (tendinopathy) occur frequently and are difficult to treat. Tendon regeneration might be improved by injecting platelet-rich plasma (PRP), an increasingly used treatment for releasing growth factors into the degenerative tendon. Objective: To examine whether a PRP injection would improve outcome in chronic midportion Achilles tendinopathy. Design, Setting, and Patients: A stratified, block-randomized, double-blind, placebo-controlled trial at a single center (The Hague Medical Center, Leidschendam, the Netherlands) of 54 randomized patients aged 18 to 70 years with chronic tendinopathy 2 to 7 cm above the Achilles tendon insertion. The trial was conducted between August 28, 2008, and January 29, 2009, with follow-up until July 16, 2009. Intervention: Eccentric exercises (usual care) with either a PRP injection (PRP group) or saline injection (placebo group). Randomization was stratified by activity level. Main Outcome Measures: The validated Victorian Institute of Sports Assessment-Achilles (VISA-A) questionnaire, which evaluated pain score and activity level, was completed at baseline and 6, 12, and 24 weeks. The VISA-A score ranged from 0 to 100, with higher scores corresponding with less pain and increased activity. Treatment group effects were evaluated using general linear models on the basis of intention-to-treat. Results: After randomization into the PRP group (n=27) or placebo group (n=27), there was complete follow-up of all patients. The mean VISA-A score improved significantly after 24 weeks in the PRP group by 21.7 points (95% confidence interval [CI], 13.0-30.5) and in the placebo group by 20.5 points (95% CI, 11.6-29.4). The increase was not significantly different between both groups (adjusted betweengroup difference from baseline to 24 weeks, -0.9; 95% CI, -12.4 to 10.6). This CI did not include the predefined relevant difference of 12 points in favor of PRP treatment. Conclusion: Among patients with chronic Achilles tendinopathy who were treated with eccentric exercises, a PRP injection compared with a saline injection did not result in greater improvement in pain and activity. Trial Registration: clinicaltrials.gov Identifier: NCT00761423.

Ferumoxides–protamine sulfate is more effective than ferucarbotran for cell labeling: implications for clinically applicable cell tracking using MRI (Article)

2010-01-01T00:00:00Z

The use of superparamagnetic iron oxide (SPIO) for labeling cells holds great promise for clinically applicable cell tracking using magnetic resonance imaging. For clinical application, an effectively and specifically labeled cell preparation is highly desired (i.e. a large amount of intracellular iron and a negligible amount of extracellular iron). In this study we performed a direct comparison of two SPIO labeling strategies that have both been reported as efficient and clinically translatable approaches. These approaches are cell labeling using ferumoxides-protamine complexes or ferucarabotran particles. Cell labeling was performed on primary human bone marrow stromal cells (hBMSCs) and chondrocytes. For both cell types ferumoxides-protamine resulted in a higher percentage of labeled cells, a higher total iron load, a larger amount of intracellular iron and a lower amount of extracellular iron aggregates, compared with ferucarbotran. Consequently, hBMSC and chondrocyte labeling with ferumoxides-protamine is more effective and results in more specific cell labeling than ferucarbotran.

Micro-CT quantification of subchondral endplate changes in intervertebral disc degeneration (Article)

2010-01-01T00:00:00Z

Background: The intervertebral disc (IVD) is dependent on nutrient provision through a cartilage layer with underlying subchondral bone, analogous to joint cartilage. In the joint, subchondral bone remodeling has been associated with osteoarthritis (OA) progression due to compromised nutrient and gas diffusion and reduced structural support of the overlaying cartilage. However, subchondral bone changes in IVD degeneration have never been quantified before. Objective: The aim of this study is to determine the subchondral bone changes at different stages of IVD degeneration by micro-CT. Methods: Twenty-seven IVDs including the adjacent vertebral endplates were obtained at autopsy. Midsagittal slices, graded according the Thompson score, were scanned. Per scan 12 standardized cylindrical volumes of interest (VOI) were selected. Six VOIs contained the bony endplate and trabeculae (endplate VOIs) and six accompanying VOIs only contained trabecular bone (vertebral VOIs). Bone volume as percentage of the total volume (BV/TV) of the VOI, trabecular thickness (TrTh) and connectivity density (CD) were determined. Results: An increase in BV/TV and TrTh was found in endplate VOIs of IVDs with higher Thompson score whereas these values remained stable or decreased in the vertebral VOIs. Conclusion: The increase in bone volume combined with the increase in TrTh in endplate VOIs strongly suggest that the subchondral endplate condenses to a more dense structure in degenerated IVDs. This may negatively influence the diffusion and nutrition of the IVD. The endplate differences between intact and mild degenerative IVDs (grade II) indicate an early association of subchondral endplate changes with IVD degeneration.

Calcineurin inhibitors promote chondrogenic marker expression of dedifferentiated human adult chondrocytes via stimulation of endogenous TGFβ1 production (Article)

2010-01-01T00:00:00Z

In vitro chondrocyte expansion is required for several cell-based approaches for the repair of chondral lesions. During expansion, loss of chondrogenic phenotype takes place (dedifferentiation). The objective of this study was to investigate calcineurin (Cn) as a potential target to improve chondrocyte phenotype for cartilage repair purposes. Cn activity in human articular chondrocytes was significantly increased during dedifferentiation and decreased during redifferentiation in vitro. Inhibition of Cn activity by FK506 increased the expression of chondrogenic markers collagen type 2, aggrecan, and SOX9 in culture-expanded cells. Addition of FK506 increased endogenous transforming growth factor 2(TGF) β1 expression on both mRNA and protein level. The effect of FK506 on chondrogenic markers was abolished by addition of anti-TGFβ1 antibody, indicating that the endogenous TGFβ1 was necessary to increase chondrogenic marker expression. We also showed that chondrocyte redifferentiation by TGFβ requires calcium influx and does not depend on changes in Cn activity. In conclusion, inhibition of Cn activity by FK506 increases the expression of chondrogenic markers via endogenous TGFβ1 production in human articular chondrocytes. Cn inhibitors might be an alternative for the application of (recombinant) TGFβ, to promote chondrocyte phenotype for cell-based cartilage repair procedures.

Dual energy x-ray absorptiometry analysis contributes to the prediction of hip osteoarthritis progression (Article)

2009-11-02T00:00:00Z

Introduction: To determine if structural bone parameters obtained from dual energy X-ray absorptiometry (DXA) contribute to the prediction of progression of hip osteoarthritis (OA) and to test if the difference between the most affected (OA) hip and the contralateral hip adds to this prediction.Methods: The study group involves a prospective cohort of 189 patients that met the American College of Rheumatology (ARC) classification criteria for hip osteoarthritis. Progression was defined as 20% joint space narrowing or total hip replacement within a two years follow up. Software was developed to calculate geometrical aspects and bone mineral density (BMD) in different regions of interest of the proximal femur. Logistic regression was used to test if Kellgren and Lawrence (K-L) scores and DXA parameters can predict progression of OA. Models were compared using -2log likelihood tests, R2Nagelkerke and areas under the Receiver Operator Characteristic curves, assessed using 10-fold cross validation.Results: The model that included the DXA variables was significantly better in predicting hip OA progression than the model with K-L score of the affected side alone (P < 0.01). The addition of the differences in DXA parameters between the most affected and contralateral hip in the superior part of the femoral head, trochanteric and intertrochanteric area further improved the prediction of progression (P < 0.05). K-L score of the affected side was still the most significant single variable in the models.Conclusions: DXA parameters can significantly contribute to the prediction of progression in patients with hip osteoarthritis. The analysis of the DXA differences between the hips of the patient represents a small but significant contribution to this prediction. These analyses show the importance of bone density changes in the etiology of OA.

Unfocused Extracorporeal Shock Wave Therapy as Potential Treatment for Osteoporosis (Article)

2009-11-01T00:00:00Z

Extracorporeal shock wave therapy (ESWT) influences the differentiation of bone marrow stroma cells towards osteoprogenitors and increases the expression of several growth factors. To assess whether unfocused ESWT might serve as a treatment for osteoporosis, we examined the bone architecture dynamics of ESWT-treated and untreated rat tibiae using in vivo micro-computed tomography (CT) scanning. In addition, the effects of ESWT on fracture healing, using a bilateral fibula osteotomy, were examined. Unilateral unfocused ESWT with 2,000 pulses and an energy flux density of 0.16 mJ/mm(2) was applied to the hind leg of ovariectomized and sham-ovariectomized rats. A single treatment with unfocused ESWT resulted in a higher trabecular bone volume fraction (BV/TV) in the proximal tibia of the sham-ovariectomized animals. Three weeks after ESWT, BV/TV was 110% of baseline BV/TV in treated legs versus 101% in untreated contralateral control legs (p = 0.001) and 105% of baseline BV/TV versus 95% at 7 weeks after ESWT (p = 0.0004). In ovariectomized rats, shock wave treatment resulted in a diminished bone loss. At 7 weeks, the BV/TV of the treated legs was 50% of baseline BV/TV, whereas in untreated control legs this was 35% (p = 0.0004). ESWT did not influence acute fracture healing. This study shows that bone microarchitecture can be affected by unfocused shock waves, and indicates that unfocused ESWT might be useful for the treatment of osteopenia and osteoporosis.

Development of osteoarthritic features in estrogen receptor knockout mice (Article)

2009-10-01T00:00:00Z

Objective: Estrogens are suggested to play a role in the development of osteoarthritis as indicated by the increased prevalence in women after menopause. We studied whether deletion of the estrogen receptor (ER) α, β, or both in female mice results in cartilage damage, osteophytosis, and changes in subchondral bone of skeletally mature animals. Methods: We studied knee joints of 6-month-old female ERα-/-, ERβ-/-, and (double) ERα-/-β-/- mice and their wild type (wt) littermates. The presence and size of osteophytes and osteoarthritic changes in cartilage were analyzed using histology. Changes in subchondral plate and trabecular bone were studied using micro-CT. Results: In ERα-/-β-/- mice, we observed an increase in number and/or size of osteophytes and thinning of the lateral subchondral plate. However, cartilage damage was not different from wt. In ERα-/- or ERβ-/- mice, no significant differences in cartilage damage score, osteophyte formation, or subchondral plate thickness were found. The bone volume fraction of the epiphyseal trabecular bone was unchanged in ERα-/- mice, increased in ERβ-/- mice, and decreased in ERα-/-β-/- mice. Conclusions: We conclude that deletion of both ERs leads to increased osteophytosis, but deletion of one or both ERs does not lead to overt cartilage damage in 6-month-old mice.

Imaging of activated macrophages in experimental osteoarthritis using folate targeted animal SPECT/CT (Article)

2009-09-09T00:00:00Z

Objective. Evaluation of macrophage activation may provide essential information about aetiology and progression rate of osteoarthritis. Activated macrophages abundantly express the folate-receptor-beta (FR-β), which can be targeted using radioactive labelled folic acid. The purpose of this study was to investigate if macrophage activation can be monitored in small animal OA models using a folate radiotracer and to test if macrophage activation differs in different models of OA and subsequent different OA progression. Methods. Two rat models of OA were used: the monoiodoacetate (MIA) model, which is a fast progressing biochemical induced model and the anterior cruciate ligament transaction (ACLT) model that induces OA at a slower pace. Images were obtained using high resolution small animal SPECT/CT. Specificity of the technique was tested by eradicating macrophages using clodronate laden liposomes and blockade of the FR-β by cold folic acid. Results. The MIA model had a high initial activation with a peak after two weeks which disappeared after eight weeks. The ACLT model showed less activation but was still active 12 weeks after induction. The technique allowed monitoring of the disease process over time, in which late stage disease showed less macrophage activation than early onset stages especially in the fast progressing MIA model for OA. Conclusion. Macrophage activation in experimental OA could clearly be demonstrated and monitored by the folate radiotracer. The high resolution, high sensitivity and high specificity of the used technique allowed clear localisation of macrophage activity in a disease model, which is not known for abundant macrophage involvement.

Ultrasonographic tissue characterisation of human Achilles tendons: quantification of tendon structure through a novel non-invasive approach (Article)

2009-08-01T00:00:00Z

OBJECTIVE: To asses if three-dimensional imaging of the Achilles tendon by Ultrasonographic Tissue Characterisation (UTC) can differentiate between symptomatic and asymptomatic tendons. DESIGN: Case-control study. SETTING: Sports medical department of The Hague medical centre. PATIENTS: Twenty-six tendons from patients with chronic midportion Achilles tendinopathy were included. The "matched" control group consisted of 26 asymptomatic tendons. INTERVENTIONS: Symptomatic and asymptomatic tendons were scanned using the UTC-procedure. One researcher performed the ultrasonographic data-collection. These blinded data were randomised and outcome measures were determined by two independent observers. Main outcome measurements: The raw ultrasonographic images were analysed with a custom-designed algorithm that quantifies the three-dimensional stability of echopatterns, qua intensity and distribution over contiguous transverse images. This three-dimensional stability was related to tendon structure in previous studies. UTC categorizes four different echo-types that represent: I) highly stable; II) medium stable; III) highly variable and IV) constantly low intensity and variable distribution. The percentages of echo-types were calculated and the maximum tendon-thickness was measured. Finally, the inter-observer reliability of UTC was determined. RESULTS: Symptomatic tendons showed less pixels in echo-types I and II than asymptomatic tendons (51.5% versus 76.6%, p<0.001), thus less three-dimensional stability of the echopattern. The mean maximum tendon thickness was 9.2 mm in the symptomatic group and 6.8 mm in the asymptomatic group (p<0.001). The Intra-class Correlation Coefficient (ICC) for the inter-observer reliability of determining the echo-types I+II was 0.95. The ICC for tendon thickness was 0.84. CONCLUSION: UTC can quantitatively evaluate tendon structure and thereby discriminate symptomatic and asymptomatic tendons. As such UTC might be useful to monitor treatment protocols.

Cell labelling with superparamagnetic iron oxide has no effect on chondrocyte behaviour (Article)

2009-07-01T00:00:00Z

BACKGROUND: Tissue engineering and regenerative medicine are two rapidly advancing fields of research offering potential for effective treatment of cartilage lesions. Today, chondrocytes are the cell type of choice for use in cartilage repair approaches such as autologous chondrocyte implantation. To verify the safety and efficacy of such approaches it is necessary to determine the fate of these transplanted cells. One way of doing this is prelabelling cells before implantation and tracking them using imaging techniques. The use of superparamagnetic iron oxide (SPIO) for tracking of cells with magnetic resonance imaging (MRI) is ideal for this purpose. It is non-radioactive, does not require viral transfection and is already approved for clinical use as a contrast agent. OBJECTIVE: The purpose of this study was to assess the effect of SPIO labelling on adult human chondrocyte behaviour. METHODS: Cells were culture expanded and dedifferentiated for two passages and then labelled with SPIO. Effect on cell proliferation was tested. Furthermore, cells were cultured for 21 days in alginate beads in redifferentiation medium. Following this period, cells were analysed for expression of cartilage-related genes, proteoglycan production and collagen protein expression. RESULTS: SPIO labelling did not significantly affect any of these parameters relative to unlabelled controls. We also demonstrated SPIO retention within the cells for the full duration of the experiment. CONCLUSIONS: This paper demonstrates for the first time the effects of SPIO labelling on chondrocyte behaviour, illustrating its potential for in vivo tracking of implanted chondrocytes.

Chondrogenic priming of human bone marrow stromal cells: A better route to bone repair? (Article)

2009-06-01T00:00:00Z

The use of bioengineered cell constructs for the treatment of bone defects has received much attention of late. Often, bone marrow stromal cells (BMSCs) are used that are in vitro stimulated toward the osteogenic lineage, aiming at intramembranous bone formation. The success of this approach has been disappointing. A major concern with these constructs is core degradation and necrosis caused by lack of vascularization. We hypothesized that stimulation of cells toward the endochondral ossification process would be more successful. In this study, we tested how in vitro priming of human BMSCs (hBMSCs) along osteogenic and chondrogenic lineages influences survival and osteogenesis in vivo. Scaffolds that were pre-cultured on chondrogenic culture medium showed collagen type II and collagen type X production. Moreover, vessel ingrowth was observed. Priming along the osteogenic lineage led to a mineralized matrix of poor quality, with few surviving cells and no vascularization. We further characterized this process in vitro using pellet cultures. In vitro, pellets cultured in chondrogenic medium showed progressive production of collagen type II and collagen type X. In the culture medium of these chondrogenic cultured pellets, vascular endothelial growth factor (VEGF) release was observed at days 14, 21, and 35. When pellets were switched to culture medium containing β-glycerophosphate, independent of the presence or absence of transforming growth factor beta (TGF-β), mineralization was observed with a concomitant reduction in VEGF and matrix metalloproteinase (MMP) release. By showing that VEGF and MMPs are produced in chondrogenically differentiated hBMSCs in vitro, we demonstrated that these cells produce factors that are known to be important for the induction of vascularization of the matrix. Inducing mineralization in this endochondral process does, however, severely diminish these capacities. Taken together, these data suggest that optimizing chondrogenic priming of hBMSCs may further improve vessel invasion in bioengineered constructs, thus leading to an alternative and superior approach to bone repair.

Effect of glucosamine sulphate on joint space narrowing, pain and function in patients with hip osteoarthritis; subgroup analyses of a randomized controlled trial (Article)

2009-04-01T00:00:00Z

Objective: Recently we reported that glucosamine sulphate (GS) did not have an effect on the symptoms and progression of primary care patients with hip osteoarthritis (OA). The aim of this present study was to investigate whether there are subgroups of patients with hip OA for whom GS might be an effective therapy. Method: We randomized 222 patients with hip OA that met one of the American College of Rheumatology criteria to either 1500 mg of oral GS or placebo once daily for 2 years. Subgroup analyses were predefined for radiographic severity (Kellgren & Lawrence (KL) = 1 vs ≥2) and for type of OA (localised vs generalised). Additional exploratory subgroup analyses focused on groups based on pain level, pain medication use, baseline joint space width (JSW), and concomitant knee OA at baseline. Primary outcome measures were Western Ontario MacMaster Universities (WOMAC) pain and function scores over 24 months, and joint space narrowing (JSN) after 24 months. Results: In the predefined subgroups based on radiographic severity and type of OA, the outcomes WOMAC pain, function and JSN were similar for the GS and placebo group. Conclusion: GS was not significantly better than placebo in reducing symptoms and progression of hip OA in subgroups of patients.

Calcineurin inhibitors promote chondrogenic marker expression of dedifferentiated human adult chondrocytes via stimulation of TGFss1 production (Article)

2009-01-01T00:00:00Z

In-vitro chondrocyte expansion is required for several cell-based approaches for the repair of chondral lesions. During expansion, loss of chondrogenic phenotype takes place (dedifferentiation). The objective of this study was to investigate calcineurin as a potential target to improve chondrocyte phenotype for cartilage repair purposes. Calcineurin activity in human articular chondrocytes was significantly increased during dedifferentiation and decreased during redifferentiation in vitro. Inhibition of calcineurin activity by FK506 increased the expression of chondrogenic markers collagen type 2, aggrecan and SOX9 in culture expanded cells. Addition of FK506 increased endogenous Transforming Growth Factor (TGF) beta1 expression on both mRNA and protein level. The effect of FK506 on chondrogenic markers was abolished by addition of anti-TGFbeta1 antibody, indicating that the endogenous TGFbeta1 was necessary to increase chondrogenic marker expression. We also showed that chondrocyte redifferentiation by TGFbeta requires calcium influx and does not depend on changes in calcineurin activity. In conclusion, inhibition of calcineurin activity by FK506 increases the expression of chondrogenic markers via endogenous TGFbeta1 production in human articular chondrocytes. Calcineurin inhibitors might be an alternative for the application of (recombinant) TGFbeta, to promote chondrocyte phenotype for cell-based cartilage repair procedures.

Calcineurin inhibitors promote chondrogenic marker expression of dedifferentiated human adult chondrocytes via stimulation of TGFss1 production (Article)

2009-01-01T00:00:00Z

Control of oxygen tension and pH in a bioreactor for cartilage tissue engineering (Article)

2008-12-22T00:00:00Z

Chondrogenic Priming of Human Bone Marrow Stromal Cells: A Better Route to Bone Repair? (Article)

2008-12-01T00:00:00Z

The use of bioengineered cell constructs for the treatment of bone defects has received much attention of late. Often, bone marrow stromal cells (BMSCs) are used that are in vitro-stimulated toward the osteogenic lineage, aiming at intramembranous bone formation. The success of this approach has been disappointing. A major concern with these constructs is core degradation and necrosis caused by lack of vascularization. We hypothesized that stimulation of cells toward the endochondral ossification process would be more successful. In this study, we tested how in vitro priming of human BMSCs (hBMSCs) along osteogenic and chondrogenic lineages influences survival and osteogenesis in vivo. Scaffolds that were pre-cultured on chondrogenic culture medium showed collagen type II and collagen type X production. Moreover, vessel ingrowth was observed. Priming along the osteogenic lineage led to a mineralized matrix of poor quality, with few surviving cells and no vascularization. We further characterized this process in vitro using pellet cultures. In vitro, pellets cultured in chondrogenic medium showed progressive production of collagen type II and collagen type X. In the culture medium of these chondrogenic cultured pellets, vascular endothelial growth factor (VEGF) release was observed at days 14, 21, and 35. When pellets were switched to culture medium containing beta-glycerophosphate, independent of the presence or absence of transforming growth factor beta (TGF-beta), mineralization was observed with a concomitant reduction in VEGF and matrix metalloproteinase (MMP) release. By showing that VEGF and MMPs are produced in chondrogenically differentiated hBMSCs in vitro, we demonstrated that these cells produce factors that are known to be important for the induction of vascularization of the matrix. Inducing mineralization in this endochondral process does, however, severely diminish these capacities. Taken together, these data suggest that optimizing chondrogenic priming of hBMSCs may further improve vessel invasion in bioengineered constructs, thus leading to an alternative and superior approach to bone repair.

Bone resorption inhibitor alendronate normalizes the reduced bone thickness of TRPV5-/- mice (Article)

2008-11-01T00:00:00Z

TRPV5 is a Ca2+-selective channel involved in transcellular Ca2+absorption expressed in kidney and in the ruffled border of osteoclasts. Studies in hypercalciuric TRPV5 knockout (TRPV5-/-) mice, which display significantly increased vitamin D levels, showed that TRPV5 ablation increases number and size of osteoclasts but impairs osteoclast-mediated bone resorption. The latter is not in line with the observed decreased bone thickness in TRPV5-/-mice. Bisphosphonates also inhibit osteoclast-mediated bone resorption. The aim of this study was to evaluate the effect of alendronate on the expression of the Ca2+transporters in bone, kidney, and duodenum and, importantly, the bone phenotype in TRPV5-/-mice. Wildtype (TRPV5+/+) and TRPV5-/-mice were treated during 10 wk with 2 mg/kg alendronate or vehicle weekly and housed in metabolic cages at the end of treatment. Urine and blood samples were taken for biochemical analysis, and duodenum, kidney, and femur were sampled. Expression of Ca2+transporters and osteoclast ruffled border transporters in bone and cultured osteoclasts was determined by QPCR analysis. Femurs were scanned using μCT, and resorption pit assays were performed in bone marrow cultures isolated from TRPV5+/+and TRPV5-/-mice. Alendronate treatment enhanced bone thickness in TRPV5+/+mice but also normalized the disturbed bone morphometry parameters in TRPV5-/-mice. Bone TRPV5 expression was specifically enhanced by alendronate, whereas the expression of Ca2+transporters in kidney and intestine was not altered. The expression of the osteoclast ruffled border membrane proteins chloride channel 7 (CLC-7) and the vacuolar H+-ATPase did not differ between both genotypes, but alendronate significantly enhanced the expression and PTH levels in TRPV5-/-mice. The expression of TRPV5, CLC-7, and H+-ATPase in osteoclast cultures was not affected by alendronate. The number of resorption pits was reduced in TRPV5-/-bone marrow cultures, but the response to vitamin D was similar to that in TRPV5+/+cultures. The alendronate-induced upregulation of TRPV5 in bone together with the decreased resorptive capacity of TRPV5-/-osteoclasts in vitro suggests that TRPV5 has an important role in osteoclast function. However, our data indicate that significant bone resorption still occurs in TRPV5-/-mice, because alendronate treatment normalized bone thickness in these mice. Thus, TRPV5-/-mice are able to rescue the resulting defect in osteoclast-mediated bone resorption, possibly mediated by the long-term hypervitaminosis D or other (non)hormonal compensatory mechanisms.

Glucosamine increases hyaluronic acid production in human osteoarthritic synovium explants (Article)

2008-10-08T00:00:00Z

Background. Glucosamine (GlcN) used by patients with osteoarthritis was demonstrated to reduce pain, but the working mechanism is still not clear. Viscosupplementation with hyaluronic acid (HA) is also described to reduce pain in osteoarthritis. The synthesis of HA requires GlcN as one of its main building blocks. We therefore hypothesized that addition of GlcN might increase HA production by synovium tissue. Methods. Human osteoarthritic synovium explants were obtained at total knee surgery and pre-cultured for 1 day. The experimental conditions consisted of a 2 days continuation of the culture with addition of N-Acetyl-glucosamine (GlcN-Ac; 5 mM), glucosamine-hydrochloride (GlcN-HCl; 0.5 and 5 mM), glucose (Gluc; 0.5 and 5 mM). Hereafter HA production was measured in culture medium supernatant using an enzyme-linked binding protein assay. Real time RT-PCR was performed for hyaluronic acid synthase (HAS) 1, 2 and 3 on RNA isolated from the explants. Results. 0.5 mM and 5 mM GlcN-HCl significantly increased HA production compared to control (approximately 2 - 4-fold), whereas GlcN-Ac had no significant effect. Addition of 5 mM Gluc also increased HA production (approximately 2-fold), but 0.5 mM Gluc did not. Gene expression of the HA forming enzymes HAS 1, 2 and 3 was not altered by the addition of GlcN or Gluc. Conclusion. Our data suggest that exogenous GlcN can increase HA production by synovium tissue and is more effective at lower concentrations than Gluc. This might indicate that GlcN exerts its potential analgesic properties through stimulation of synovial HA production.

Het effect van glucosaminesulfaat op de progressie van heupartrose (Article)

2008-10-01T00:00:00Z

Introduction: Het effect van glucosaminesulfaat bij de behandeling van artrose is omstreden. Een systematische review uit 2005 met twintig onderzoeken kon geen definitieve conclusie trekken.1 Van de vijftien onderzoeken die glucosamine vergeleken met een placebo was het algehele effect op pijn gemiddeld weliswaar in het voordeel van glucosamine, maar meer dan de helft van deze onderzoeken vond geen verschil tussen glucosamine en een placebo. Ook recente onderzoeken gaven geen duidelijkheid.2-4 Uit eerdere onderzoeken kon men concluderen dat patiënten met milde radiologische artrose meer baat zouden hebben bij glucosamine dan patiënten met een ernstiger ziektebeeld.5,6 We vonden slechts twee onderzoeken over het effect van glucosaminesulfaat op radiologische progressie,10,11 waarbij bovendien discussie ontstond over het radiologisch protocol.12-14 Daarom is verder onderzoek nodig. Tot nu toe is vooral het effect van glucosamine op knieartrose onderzocht, slechts drie onderzoeken includeerden ook patiënten met andere aangedane gewrichten.7-9 Wij vonden geen onderzoeken bij patiënten met heupartrose. En hoewel knieartrose meer voorkomt, komt heupartrose voldoende voor om het effect van glucosamine bij deze groep te testen. Al met al genoeg aanleiding voor een tweejarig, geblindeerd, gerandomiseerd, placebo-gecontroleerd onderzoek naar het effect van glucosaminesulfaat op de symptomatische en radiologische progressie van eerstelijns patiënten met heupartrose.

Imaging of experimental osteoarthritis in small animal models (Article)

2008-09-30T00:00:00Z

Normally, tissue alterations in small animal models for osteoarthritis (OA) are assessed by time-consuming and destructive histology or biochemical assays. Some high resolution imaging modalities are used for longitudinal monitoring of the OA disease process in vivo. μCT is one of these imaging modalities, which is known for superb high-resolution imaging of bone architecture alterations. A major drawback of μCT is that it has low soft-tissue contrast, which makes direct imaging of cartilage impossible. The use of μCT in combination with negatively charged radiopaque contrast agents enables imaging of cartilage degeneration. We demonstrate the possibility of μCT to image cartilage degeneration as a consequence of experimental OA, by the use contrast enhanced μCT in vivo in a rat model for OA. Furthermore, for the assessment of alterations in molecular processes involved in OA we used the recently developed technique of multi pinhole SPECT. This enables us to assess molecular processes involved in experimental OA in a rat at sub-millimeter level. Here we show quantification of subchondral bone turnover in an OA rat knee. These new techniques demonstrate the possibilities of quantitative experimental OA assessment in small animal models such as mice and rats and might enable substitution of the conventional destructive methods.

In vivo imaging of cartilage degeneration using microCT-arthrography (Article)

2008-09-01T00:00:00Z

OBJECTIVE: In vivo imaging of cartilage degeneration in small animal models is nowadays practically impossible. In the present study, we investigated the use of micro-computed tomography (microCT) in combination with a negatively charged ionic iodine dimer (ioxaglate) for in vivo assessment of cartilage degeneration in a small animal model. METHODS: Cartilage degeneration was induced in the right knee of rats by injection of mono-iodoacetate (MIA). We imaged the rat knees with ioxaglate enhanced microCT-arthrography at 4, 16 and 44 days after MIA injection. Subsequently, microCT-arthrographic findings were evaluated and compared with quantitative histology of the patellar cartilage. RESULTS: In vivo microCT-arthrography clearly detected cartilage degeneration in the rat knee-joints, in which the ioxaglate diffused into the degenerated cartilage layer. Higher microCT-attenuation values and smaller total volumes of the cartilage layer were detected at longer time periods after MIA injection, which is quantitatively confirmed by histology. CONCLUSION: In vivo microCT-arthrography is a valuable tool for detection of minor cartilage alterations and distinguishes different stages of cartilage degeneration in a small animal model. Since microCT, at the same time, also visualizes osteophyte formation and changes in the underlying subchondral bone structures, the technique will be very useful for longitudinal overall assessment of the development of (osteo)arthritis and to study interventions in small animal models.

Can platelet-rich plasma enhance tendon repair? A cell culture study (Article)

2008-06-01T00:00:00Z

BACKGROUND: Autologous platelet-rich plasma (PRP) application appears to improve tendon healing in traumatic tendon injuries, but basic knowledge of how PRP promotes tendon repair is needed. HYPOTHESIS: Platelet-rich plasma has a positive effect on cell proliferation and collagen production and induces the production of matrix-degrading enzymes and endogenous growth factors by human tenocytes. STUDY DESIGN: Controlled laboratory study. METHODS: Human tenocytes were cultured 14 days in 2% fetal calf serum medium complemented with 0%, 10%, or 20% vol/vol platelet-rich clot releasate ([PRCR] the active releasate of PRP) or platelet-poor clot releasate (PPCR). At day 4, 7, and 14, cell amount, total collagen, and gene expression of collagen I alpha 1 (COL1) and III alpha 1 (COL3), matrix metalloproteinases ([MMPs] MMP1, MMP3, and MMP13), vascular endothelial-derived growth factor (VEGF)-A, and transforming growth factor (TGF)-beta1 were analyzed. RESULTS: Platelet numbers in PRP increased to 2.55 times baseline. Growth-factor concentrations of VEGF and platelet-derived growth factor (PDGF)-BB were higher in PRCR than PPCR. Both PRCR and PPCR increased cell number and total collagen, whereas they decreased gene expression of COL1 and COL3 without affecting the COL3/COL1 ratio. PRCR, but not PPCR, showed upregulation of MMP1 and MMP3 expression. Matrix metalloproteinase 13 expression was not altered by either treatment. PRCR increased VEGF-A expression at all time points and TGF-beta1 expression at day 4. CONCLUSION: In human tenocyte cultures, PRCR, but also PPCR, stimulates cell proliferation and total collagen production. PRCR, but not PPCR, slightly increases the expression of matrix-degrading enzymes and endogenous growth factors. CLINICAL RELEVANCE: In vivo use of PRP, but also of PPP to a certain extent, in tendon injuries might accelerate the catabolic demarcation of traumatically injured tendon matrices and promote angiogenesis and formation of a fibrovascular callus. Whether this will also be beneficial for degenerative tendinopathies remains to be elucidated.

Animal models for osteoarthritis: the effect of ovariectomy and estrogen treatment - a systematic approach (Article)

2008-05-01T00:00:00Z

OBJECTIVE: The prevalence of osteoarthritis (OA) increases dramatically in women after the age of 50. Animal models are used to study the effects of hormone depletion [by ovariectomy (OVX)] and estrogen treatment on OA. This review summarizes these animal studies, in order to get a better insight in the role of hormones on OA. METHOD: The literature was systematically reviewed until May 2007. The results were divided into two parts: the effect of OVX on cartilage, and the effect of estrogen treatment on cartilage. Only studies with an appropriate control group (e.g., sham-operated) were included. RESULTS AND DISCUSSION: Eleven out of 16 animal studies showed that OVX resulted in cartilage damage. When only studies using sexually mature animals were included, we saw that 11 out of 14 studies showed a detrimental effect, indicating considerable evidence for a relation between cartilage degeneration and OVX in mature animals. The effect of estrogen treatment was inconclusive with only 11 out of 22 animal studies reporting a beneficial effect on cartilage, whereas all six studies administering selective estrogen receptor modulators (SERMs) after OVX described protective effects. The discrepancy between the studies may be caused by the large variation in experimental set-up. We suggested a list of quality criteria for animal models since standardisation of design and outcome parameters of animal experiments may help to compare different studies and to gain better insight in the role of hormones in the osteoarthritic process.

Control of oxygen tension and pH in a bioreactor for cartilage tissue engineering (Article)

2008-05-01T00:00:00Z

Introduction (instead of abstract)
Environmental parameters such as oxygen tension and extracellular pH are believed to play a crucial role in successful tissue engineering. Identifying the optimal values of such parameters and understanding the cellular mechanisms that they govern are essential steps in the tissue engineering process. Cartilage, for example, is well known for its avascularity and its naturally hypoxic state in vivo. However, mimicking this hypoxic state in vitro does not automatically translate to improved tissue engineering results. In fact, the effect of hypoxia on chondrocytes appears to differ between species, differentiation state and metabolic condition [1]. Similarly, while chondrocytes are generally believed to experience a slightly acidic environment, a pH of approximately 7.2 seems to be favored for matrix synthesis [2], as lower values appear to inhibit GAG deposition [3]. Unfortunately, the mechanism by which pH influences matrix synthesis remains unknown. Moreover, the effects of oxygen tension and pH can also vary with medium composition if they exert an effect on, for example, growth factor functionality. We investigated the functionality of a new bioreactor, that allows independent control of oxygen tension and pH in 24 individual wells, for tissue engineering purposes. Accuracy and consistency of control were examined and an experiment was performed with human articular chondrocytes using oxygen and pH control to evaluate this bioreactor in a relevant tissue engineering application.

Effects of iron oxide incorporation for long term cell tracking on MSC differentiation in vitro and in vivo (Article)

2008-05-01T00:00:00Z

Successful cell therapy will depend on the ability to monitor transplanted cells. With cell labeling, it is important to demonstrate efficient long term labeling without deleterious effects on cell phenotype and differentiation capacity. We demonstrate long term (7 weeks) retention of superparamagnetic iron oxide particles (SPIO) by mesenchymal stem cells (MSCs) in vivo, detectable by MRI. In vitro, multilineage differentiation (osteogenic, chondrogenic and adipogenic) was demonstrated by histological evaluation and molecular analysis in SPIO labeled and unlabeled cells. Gene expression levels were comaparable to unlabeled controls in adipogenic and chondrogenic conditions however not in the osteogenic condition. MSCs seeded into a scaffold for 21 days and implanted subcutaneously into nude mice for 4 weeks, showed profoundly altered phenotypes in SPIO labeled samples compared to implanted unlabeled control scaffolds, indicating chondrogenic differentiation. This study demonstrates long term MSC traceability using SPIO and MRI, uninhibited multilineage MSC differentiation following SPIO labeling, though with subtle but significant phenotypical alterations.

Cartilage damage pattern in relation to subchondral plate thickness in a collagenase-induced model of osteoarthritis (Article)

2008-04-01T00:00:00Z

OBJECTIVE: To see how initial differences in subchondral bone phenotype influence the development of cartilage damage and changes in subchondral bone architecture in an osteoarthritis (OA)-induced mouse model. METHOD: Intra-articular collagenase injections (right knee joint) and saline controls (left knee joint) were applied in the knees of two mouse strains known to have either a low or a high bone mass phenotype: the low bone mass C57Bl/6 mice with a thin subchondral bone plate and high bone mass C3H/HeJ mice with a thick subchondral bone plate. The ages of the mice were 16 and 30 weeks, with n=8 per group. The collagenase injection induced an osteoarthritic phenotype that was evaluated 4 weeks later in the tibia using histological analyses and micro-computed tomography (micro-CT). RESULTS: Both strains developed cartilage damage in the collagenase-injected right knee joints to a comparable extent, however, the spatial distribution of cartilage damage differed significantly: C57Bl/6 mice had most damage at the postero-lateral side, whereas in C3H/HeJ mice the postero-medial region was the most affected. Spontaneous cartilage damage was found in the saline-injected left control knees of C57Bl/6 mice, but in C3H/HeJ mice spontaneous cartilage damage was virtually absent. In both strains the subchondral bone plate of collagenase-injected joints became thinner, independent of the site of cartilage damage. TRAP-positive osteoclasts were observed underneath the subchondral bone plate, in line with the observed decreased thickness. No link was found between subchondral bone plate thickness and cartilage damage in the collagenase-injected joints. The subchondral trabecular architecture only changed in the high bone mass C3H/HeJ mice, with thinning of trabeculae and increased trabecular spacing. CONCLUSION: Thinning of the subchondral bone plate was found as a common observation 4 weeks after OA had been induced in two strains of mice having either a high or low bone phenotype, but no relation was found with the amount of cartilage damage. In addition, this study shows that different strains of mice can react differently to instability-induced OA with respect to the spatial arrangement of cartilage damage and changes in subchondral trabecular structure.

Single versus triple daily activation of the distractor: no significant effects of frequency of distraction on bone regenerate quantity and architecture (Article)

2008-04-01T00:00:00Z

OBJECTIVES: To study the effect of two different frequencies of distraction on the quantity and architecture of bone regenerate using micro-computed tomography, and to determine whether radiographic and ultrasonographic bone-fill scores provide reliable predictive value for the amount of new bone in the distraction area. MATERIAL AND METHODS: Twenty-six skeletally mature rabbits underwent three full days of latency, after which midface distraction was started. Low-frequency group (n=12): a distraction rate of 0.9 mm/d achieved by one daily activation for 11 days to create a 10mm distraction gap. High-frequency group (n=12): idem, but three daily activations were used instead of one. Control group (n=2) underwent no distraction. After 21 days of consolidation, bone-fill in the distraction area was assessed by means of ultrasonography and radiography. Micro-computed tomography was used to quantify new bone formation and bone architecture. RESULTS: Relative bone volume (BV/TV) showed a tendency towards a difference (P=0.09) between the low and high-frequency groups. No significant differences were found for bone architecture. No significant correlation between BV/TV values and bone-fill scores was found. CONCLUSIONS: An increase in rhythm from one to three activations daily does not create significantly more bone. Bone-fill score values provided no reliable predictive value for the amount of new bone formation.

In vitro expansion affects the response of chondrocytes to mechanical stimulation (Article)

2008-03-01T00:00:00Z

OBJECTIVE: Expansion of autologous chondrocytes is a common step in procedures for cartilage defect repair. Subsequent dedifferentiation can alter cellular response to mechanical loading, having major consequences for the cell's behavior in vivo after reimplantation. Therefore, we examined the response of primary and expanded human articular chondrocytes to mechanical loading. METHOD: Primary and expanded chondrocytes were stretched at either 0.5% or 3.0% at 0.5Hz, 2h per day, for 3 days. Gene expression levels of matrix components (aggrecan (AGC1), lubricin (PRG4), collagen type I (COL1), type II (COL2) and type X (COL10)) as well as matrix enzymes (matrix metalloproteinase 1 (MMP1), MMP3, MMP13) and SOX9 were compared to unstretched controls. To evaluate the effect of a chondrogenic environment on cellular response to stretch, redifferentiation medium was used on expanded cells. RESULTS: In primary chondrocytes, stretch led to mild decreases in AGC1, COL1 and COL10 gene expression (maximum of 3.8-fold) and an up-regulation of PRG4 (2.0-fold). In expanded chondrocytes, expression was down-regulated for AGC1 (up to 21-fold), PRG4 (up to 5.0-fold), COL1 (10-fold) and COL2 (2.9-fold). Also, expression was up-regulated for MMP1 (20-fold) and MMP3 (up to 4-fold), while MMP13 was down-regulated (2.8-fold). A chondrogenic environment appeared to temper effects of stretch. DISCUSSION: Our results show that expansion alters the response of human chondrocytes to stretch. Expanded chondrocytes greatly decrease gene expression of matrix constituents and increase expression of MMPs, whereas primary chondrocytes hardly respond. Our data could be a reference for optimization of cell sources or expansion protocols for reimplanted chondrocytes.

Contribution of collagen network features to functional properties of engineered cartilage (Article)

2008-03-01T00:00:00Z

BACKGROUND: Damage to articular cartilage is one of the features of osteoarthritis (OA). Cartilage damage is characterised by a net loss of collagen and proteoglycans. The collagen network is considered highly important for cartilage function but little is known about processes that control composition and function of the cartilage collagen network in cartilage tissue engineering. Therefore, our aim was to study the contribution of collagen amount and number of crosslinks on the functionality of newly formed matrix during cartilage repair. METHODS: Bovine articular chondrocytes were cultured in alginate beads. Collagen network formation was modulated using the crosslink inhibitor beta-aminopropionitrile (BAPN; 0.25mM). Constructs were cultured for 10 weeks with/without BAPN or for 5 weeks with BAPN followed by 5 weeks without. Collagen deposition, number of crosslinks and susceptibility to degradation by matrix metalloproteinase-1 (MMP-1) were examined. Mechanical properties of the constructs were determined by unconfined compression. RESULTS: BAPN for 5 weeks increased collagen deposition accompanied by increased construct stiffness, despite the absence of crosslinks. BAPN for 10 weeks further increased collagen amounts. Absence of collagen crosslinks did not affect stiffness but ability to hold water was lower and susceptibility to MMP-mediated degradation was increased. Removal of BAPN after 5 weeks increased collagen amounts, allowed crosslink formation and increased stiffness. DISCUSSION: This study demonstrates that both collagen amounts and its proper crosslinking are important for a functional cartilage matrix. Even in conditions with elevated collagen deposition, crosslinks are needed to provide matrix stiffness. Crosslinks also contribute to the ability to hold water and to the resistance against degradation by MMP-1

A role for subchondral bone changes in the process of osteoarthritis; a micro-CT study of two canine models (Article)

2008-02-01T00:00:00Z

BACKGROUND: This study evaluates changes in peri-articular bone in two canine models for osteoarthritis: the groove model and the anterior cruciate ligament transection (ACLT) model. METHODS: Evaluation was performed at 10 and 20 weeks post-surgery and in addition a 3-weeks time point was studied for the groove model. Cartilage was analysed, and architecture of the subchondral plate and trabecular bone of epiphyses was quantified using micro-CT. RESULTS: At 10 and 20 weeks cartilage histology and biochemistry demonstrated characteristic features of osteoarthritis in both models (very mild changes at 3 weeks). The groove model presented osteophytes only at 20 weeks, whereas the ACLT model showed osteophytes already at 10 weeks. Trabecular bone changes in the groove model were small and not consistent. This contrasts the ACLT model in which bone volume fraction was clearly reduced at 10 and 20 weeks (15-20%). However, changes in metaphyseal bone indicate unloading in the ACLT model, not in the groove model. For both models the subchondral plate thickness was strongly reduced (25-40%) and plate porosity was strongly increased (25-85%) at all time points studied. CONCLUSION: These findings show differential regulation of subchondral trabecular bone in the groove and ACLT model, with mild changes in the groove model and more severe changes in the ACLT model. In the ACLT model, part of these changes may be explained by unloading of the treated leg. In contrast, subchondral plate thinning and increased porosity were very consistent in both models, independent of loading conditions, indicating that this thinning is an early response in the osteoarthritis process.

ADAMTS5-/- mice have less subchondral bone changes after induction of osteoarthritis through surgical instability: implications for a link between cartilage and subchondral bone changes (Article)

2008-01-01T00:00:00Z

Objective: Osteoarthritis (OA) is characterized by damaged articular cartilage and changes in subchondral bone. Previous work demonstrated aggrecanase-2 deficient (ADAMTS5-/-) mice to be protected from cartilage damage induced by joint instability. This study analyzed whether this protective effect on cartilage is also reflected in the subchondral bone structure. Methods: Right knee joints from 10-week old male wild type (WT) and ADAMTS5-/- mice received transection of the medial meniscotibial ligament to induce OA, whereas left knees were left unoperated. After 8 weeks knee joints were scanned by micro-CT. The proximal tibia was selected for further analysis. Histology was performed to evaluate cartilage damage and osteoclast presence. Results: ADAMTS5-/- joints had a significantly thinner subchondral plate and less epiphyseal trabecular bone compared to WT joints. Histology confirmed previous findings that ADAMTS5-/- mice have significantly less cartilage damage than WT in the instability-induced OA model. Although the subchondral bone plate became significantly thicker at the medial tibial plateau in operated joints of both genotypes, the percentage increase was significantly smaller in ADAMTS5-/- mice (WT: 20.7 ± 4.7%, ADAMTS5-/-: 8.3 ± 1.2% compared to the left unoperated control joint). In ADAMTS5-/- animals a significant decrease was found in both Oc.N./BS and Oc.S./BS. Finally, in WT but not in ADAMTS5-/- mice a significant correlation was found between medial subchondral bone plate thickness and cartilage damage at the medial tibial plateau. Conclusion: ADAMTS5-/- joints that were protected from cartilage damage showed minor changes in the subchondral bone structure, in contrast to WT mice where substantial changes were found. This finding suggests links between the process of cartilage damage and subchondral bone changes in instability-induced OA.

Glucosamine reduces anabolic as well as catabolic processes in bovine chondrocytes cultured in alginate (Article)

2007-11-01T00:00:00Z

OBJECTIVE: To investigate the working mechanism of glucosamine (GlcN) by studying the effect of different GlcN derivatives on bovine chondrocytes in alginate beads under anabolic and catabolic culture conditions. METHODS: Bovine chondrocytes seeded in alginate beads were treated with different concentrations of glucosamine-sulfate (GlcN-S), glucosamine-hydrochloride (GlcN-HCl) or N-acetyl-glucosamine (GlcN-Ac). Culture conditions were anabolic, 3 day pre-culture followed by 14 days' treatment; catabolic, extracellular matrix (ECM) breakdown induced by 10ng/ml interleukin-1beta (IL-1beta); or a situation with balance between ECM breakdown and synthesis, 24 days' pre-culture followed by 14 days' treatment. The outcome measurements were total glycosaminoglycan (GAG) and DNA content per bead. RESULTS: In the situation with balance between ECM breakdown and synthesis, GlcN-Ac had a small stimulatory effect on total GAG content. GlcN-S and GlcN-HCl had no effect. Under anabolic condition 5mM GlcN-S and GlcN-HCl significantly reduced total GAG content. GlcN-Ac did not show this effect. IL-1beta induced catabolic effects were prevented by adding 5mM GlcN-HCl. Interference of GlcN with glucose (Gluc) was demonstrated by adding extra Gluc to the medium in the anabolic culture conditions. Increasing extracellular Gluc concentrations diminished the effect of GlcN. CONCLUSION: GlcN-S and GlcN-HCl, but not GlcN-Ac, reduce anabolic and catabolic processes. For anabolic processes this was demonstrated by decreased ECM synthesis, for catabolic processes by protection against IL-1beta mediated ECM breakdown. This might be due to interference of GlcN with Gluc utilization. We suggest that the claimed structure modifying effects of GlcN are more likely based on protection against ECM degradation than new ECM production.

Early identification of radiographic osteoarthritis of the hip using an active shape model to quantify changes in bone morphometric features: can hip shape tell us anything about the progression of osteoarthritis? (Article)

2007-11-01T00:00:00Z

OBJECTIVE: Few methods exist to measure the progression of osteoarthritis (OA) or to identify people at high risk of developing OA. Striking radiographic changes include deformation of the femoral head and osteophyte growth, which are usually measured semiquantitatively following visual assessment. In this study, an active shape model (ASM) of the proximal femur was used to determine whether morphologic changes to the bone could be quantified and used as a marker of hip OA. METHODS: One hundred ten subjects who had no signs of radiographic hip OA at baseline (Kellgren/Lawrence [K/L] scores 0-1) were selected from the Rotterdam Study cohort of subjects ages > or = 55 years. To measure the progression of OA, subjects were followed up with radiographic assessment after 6 years. At the 6-year followup, 55 subjects had established OA (K/L score 3), and in 12 of these OA subjects, the progression of the disease required a total hip replacement (THR). Age- and sex-matched control subjects had a K/L score of 0 at followup. Using the ASM, subjects were assessed for shape changes in the femoral head and neck before, during, and after the development of radiographic OA. Scores of shape variance, or mode scores, were assigned for 10 modes of variation in each subject, and differences in mode scores were determined. RESULTS: During followup, significant changes in shape of the proximal femur occurred within the OA group from baseline to followup (P < 0.0001 for mode 1 and P = 0.002 for mode 6) but not within the control group. At baseline (all subjects having K/L scores 0-1), there were significant differences in mode 6 between the OA group and the control group (P = 0.020), and in modes 3 and 6 between the OA subjects who underwent THR and the remaining OA subjects (P = 0.012 and P = 0.019, respectively). CONCLUSION: Compared with traditional scoring methods, the ASM can be used more precisely to quantify the deforming effect of OA on the proximal femur and to identify, at an earlier stage of disease, those subjects at highest risk of developing radiographic OA or needing a THR. The ASM may therefore be useful as an imaging biomarker in the assessment of patients with hip OA.

Recommendations for optimal distraction protocols for various animal models on the basis of a systematic review of the literature (Article)

2007-10-01T00:00:00Z

The principles of orthopaedic distraction osteogenesis (DO) have been successfully applied to the craniofacial skeleton, but the latency time, rate and rhythm of distraction, and length of the consolidation period that are optimal for long-bone distraction may be suboptimal for craniofacial DO. The aim of this study was to provide recommendations for optimal distraction parameters in animal experimental research on craniofacial DO. The data used were from studies, added to the PubMed database between 1 January 1973 and 1 January 2007, on the outcome of DO resulting from variations in a single distraction parameter while standardizing the other distraction parameters. Although experimental animal group sizes were rather small, especially in those studies that used large animals, and both skeletally mature and immature animals were used, the (in most cases quantitative) data provided useful information on the optimal parameters in craniofacial DO. A latency period may not be necessary at all. Distraction should be performed at a rate of 1mm/day (this may be halved when small animals such as rats are used) preferably with a continuous rhythm, followed by a consolidation period of 6-8 weeks. These recommendations can be used as basic guidelines for further animal experimental studies on craniofacial DO.

Effects of microarchitecture on bone strength (Article)

2007-06-01T00:00:00Z

Bone strength and stiffness depend strongly on bone mass, but they also depend on the microarchitecture and tissue quality of both cancellous and cortical bone. All these aspects differ between individuals and between anatomic sites. This review discusses ways to characterize the three-dimensional cancellous architecture as well as changes in architecture and bone composition caused by bone remodeling. The methods used range from detailed descriptions of sizes and distances in cancellous bone to coarser texture analysis methods using clinical data. As the resolution of clinical images increases, it may become possible to use knowledge of the relationship between bone microarchitecture and strength to predict fracture risk clinically. Copyright

Long-term fluoxetine administration does not result in major changes in bone architecture and strength in growing rats (Article)

2007-05-01T00:00:00Z

Many studies have indicated that serotonin and its transporter play a role in bone metabolism. In this study we investigated the effect of selective serotonin re-uptake inhibitor (SSRI), fluoxetine (Prozac) on bone architecture and quality in growing female rats. We therefore administrated rats with clinically relevant doses of fluoxetine for a period of 6 months. DXA scans were performed during the treatment period in order to follow parameters as body weight, fat percentage and BMD. After 6 months of treatment, femurs were used to analyze bone architecture and bone strength, by means of microCT scans and three-point bending assays, respectively. We found a slightly diminished bone quality, reflected in a lower bone tissue strength, which was compensated by changes in bone geometry. As leptin and adiponectin could be possible factors in the serotonergic regulation of bone metabolism, we also determined the levels of these factors in plasma samples of all animals. Leptin and adiponectin levels were not different between the control group and fluoxetine-treated group, indicating that these factors were not involved in the observed changes in bone geometry and quality.

Intrinsic differentiation potential of adolescent human tendon tissue: an in-vitro cell differentiation study (Article)

2007-02-23T00:00:00Z

Tendinosis lesions show an increase of glycosaminoglycan amount, calcifications, and lipid accumulation. Therefore, altered cellular differentiation might play a role in the etiology of tendinosis. This study investigates whether adolescent human tendon tissue contains a population of cells with intrinsic differentiation potential. METHODS: Cells derived from adolescent non-degenerative hamstring tendons were characterized by immunohistochemistry and FACS-analysis. Cells were cultured for 21 days in osteogenic, adipogenic, and chondrogenic medium and phenotypical evaluation was carried out by immunohistochemical and qPCR analysis. The results were compared with the results of similar experiments on adult bone marrow-derived stromal cells (BMSCs). RESULTS: Tendon-derived cells stained D7-FIB (fibroblast-marker) positive, but alpha-SMA (marker for smooth muscle cells and pericytes) negative. Tendon-derived cells were 99% negative for CD34 (endothelial cell marker), and 73% positive for CD105 (mesenchymal progenitor-cell marker). In adipogenic medium, intracellular lipid vacuoles were visible and tendon-derived fibroblasts showed upregulation of adipogenic markers FABP4 (fatty-acid binding protein 4) and PPARG (peroxisome proliferative activated receptor gamma). In chondrogenic medium, some cells stained positive for collagen 2 and tendon-derived fibroblasts showed upregulation of collagen 2 and collagen 10. In osteogenic medium Von Kossa staining showed calcium deposition although osteogenic markers remained unaltered. Tendon-derived cells and BMCSs behaved largely comparable, although some distinct differences were present between the two cell populations. CONCLUSION: This study suggests that our population of explanted human tendon cells has an intrinsic differentiation potential. These results support the hypothesis that there might be a role for altered tendon-cell differentiation in the pathophysiology of tendinosis.

Histogram-based selective deblurring to improve computed tomography imaging of calcifications (Article)

2007-01-01T00:00:00Z

OBJECTIVES: Computed tomography (CT) imaging of small high-density structures, eg, calcifications, is hampered by image blur. This study aims to deconvolve calcifications in the transverse and longitudinal directions while avoiding noise amplification and edge-ringing artifacts in the surrounding low-density structures. MATERIALS AND METHODS: A method referred to as histogram-based selective deblurring (HiSD) has been developed to generate a restored image by combining the low-intensity (ie, Hounsfield Units) information of the original image with the high-intensity information of the deconvolved image. HiSD is evaluated on phantom and in vitro atherosclerotic plaque CT images by comparing the original and restored images with their corresponding reference micro-CT images both qualitatively and quantitatively. RESULTS: HiSD reduces calcification blur in the transverse and longitudinal directions without introducing noise and ringing-artifacts in the surrounding tissues. Calcification area and volume measurements are significantly improved in the restored images (reducing on average overestimation by 32% and 83%, respectively). CONCLUSIONS: HiSD significantly improves CT visualization and quantification of small high-density structures imaged in vitro.

Biochemical and functional modulation of the cartilage collagen network by IGF1, TGFbeta2 and FGF2 (Article)

2006-11-01T00:00:00Z

OBJECTIVE: Examine effects of insulin-like growth factor 1 (IGF1), transforming growth factor beta2 (TGFbeta2) and fibroblast growth factor 2 (FGF2) on proteoglycan and collagen network and biomechanical properties of the newly formed cartilage matrix. METHODS: Bovine articular chondrocytes were cultured in alginate beads for 3 weeks with or without FGF2, TGFbeta2 or IGF1 in the presence of 10% FCS. Proteoglycan content, collagen content, hydroxylysylpyridinoline cross-links and overall matrix metalloproteinase (MMP) activity in the culture medium were measured. Alginate disks cultured for 5 weeks were used to evaluate the effect of growth factors on mechanical properties of the construct by determining the equilibrium aggregate modulus and secant modulus. RESULTS: IGF1 increased collagen and proteoglycan deposition. FGF2 mainly decreased collagen deposition and TGFbeta2 proteoglycan deposition. A decrease in cross-links was observed in matrix produced by chondrocytes cultured in the presence of TGFbeta2. IGF1 and FGF2 had no influence on the number of cross-links per collagen molecule. Overall MMP activity was significantly higher in culture medium of cells cultured with FGF2. TGFbeta2 and IGF1 had no effect on MMP activity. After 35 days of culture, the matrix produced under influence of IGF1 had a lower permeability and a trend to increase stiffness. FGF2 showed a trend to lower both properties. TGFbeta2 had no effect on these parameters. CONCLUSION: IGF1, TGFbeta2 and FGF2 had differential effects on collagen network formation. Of the three growth factors tested, IGF1 seems to be best in promoting the formation of a functional collagen network since it increased proteoglycan and collagen deposition and improved the mechanical properties.

The novel vitamin D analog ZK191784 as an intestine-specific vitamin D antagonist (Article)

2006-10-01T00:00:00Z

Vitamin D [1,25(OH)2D3] plays a crucial role in Ca2+ homeostasis by stimulating Ca2+ (re)absorption and bone turnover. The 1,25(OH)2D3 analog ZK191784 was recently developed to dissociate the therapeutic immunomodulatory activity from the hypercalcemic side effects of 1,25(OH)2D3 and contains a structurally modified side chain characterized by a 22,23-double bond, 24R-hydroxy group, 25-cyclopropyl ring, and 5-butyloxazole unit. We investigated the effect of ZK191784 on Ca2+ homeostasis and the regulation of Ca2+ transport proteins in wild-type (WT) mice and mice lacking the renal epithelial Ca2+ channel TRPV5 (TRPV5-/-). The latter display hypercalciuria, hypervitaminosis D, increased intestinal expression of the epithelial Ca2+ channel TRPV6, the Ca2+-binding protein calbindin-D(9K), and intestinal Ca2+ hyperabsorption. ZK191784 normalized the Ca2+ hyperabsorption and the expression of intestinal Ca2+ transport proteins in TRPV5-/- mice. Furthermore, the compound decreased intestinal Ca2+ absorption in WT mice and reduced 1,25(OH)2D3-dependent 45Ca2+ uptake by Caco-2 cells, substantiating a 1,25(OH)2D3-antagonistic action of ZK191784 in the intestine. ZK191784 increased renal TRPV5 and calbindin-D(28K) expression and decreased urine Ca2+ excretion in WT mice. Both 1,25(OH)2D3 and ZK191784 enhanced transcellular Ca2+ transport in primary cultures of rabbit connecting tubules and cortical collecting ducts, indicating a 1,25(OH)2D3-agonistic effect in kidney. ZK191784 enhanced bone TRPV6 mRNA levels and 1,25(OH)2D3 as well as ZK191784 stimulated secretion of the bone formation marker osteocalcin in rat osteosarcoma cells, albeit to a different extent. In conclusion, ZK191784 is a synthetic 1,25(OH)2D3 ligand displaying a unique tissue-specific profile when administered in vivo. Because ZK191784 acts as an intestine-specific 1,25(OH)2D3 antagonist, this compound will be associated with less hypercalcemic side effects compared with the 1,25(OH)2D3 analogs currently used in clinical practice.

Strength of cancellous bone trabecular tissue from normal, ovariectomized and drug-treated rats over the course of ageing (Article)

2006-08-01T00:00:00Z

Hormone therapy (HT) drugs and bisphosphonates prevent osteoporosis by inhibiting osteoclastic bone resorption. However, the effects of osteoporosis and anti-resorptive drugs on the mechanical behavior of the bone tissue constituting individual trabeculae have not yet been quantified. In this study, we test the hypothesis that the mechanical properties of bone trabecular tissue will differ for normal, ovariectomized and drug-treated rat bones over the course of ageing. Microtensile testing is carried on individual trabeculae from tibial bone of ovariectomized (OVX) rats, OVX rats treated with tibolone and placebo-treated controls. The method developed minimizes errors due to misalignment and stress concentrations at the grips. The local mineralization of single trabeculae is compared using micro-CT images calibrated for bone mineral content assessment. Our results indicate that ovariectomy in rats increases the stiffness, yield strength, yield strain and ultimate stress of the mineralized tissue constituting trabecular bone relative to normal; we found significant differences (P < 0.05) at 14, 34 and 54 weeks of treatment. These increases are complemented by a significant increase in the mineral content at the tissue level, although overall bone mineral density and mass are reduced. With drug treatment, the properties remain at, or slightly below, the placebo-treated controls levels for 54 weeks. The higher bone strength in the OVX group may cause the trabecular architecture to adapt as seen during osteopenia/osteoporosis, or alternately it may compensate for loss of trabecular architecture. These findings suggest that, in addition to the effects of osteoporosis and subsequent treatment on bone architecture, there are also more subtle processes ongoing to alter bone strength at the tissue level.

Stretch-induced modulation of matrix metalloproteinases in mineralizing osteoblasts via extracellular signal-regulated kinase-1/2 (Article)

2006-07-01T00:00:00Z

Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) produced by osteoblasts play an essential role in bone remodeling. Hence, these proteins could provide an interesting means by which mechanical loading leads to adaptation of bone. Here, we examined the effect of stretch on MMP-1, -2, -3, -8, -9, -13, and -14, as well as TIMP-1 and -2 gene expression in differentiating, mineralizing, and nonmineralizing human SV-40 immortalized preosteoblast cells. In the mineralizing osteoblast culture, but not in the nonmineralizing cultures, cyclic stretch for only 15 min resulted in an increase of MMP-1 (fourfold) and -3 (depending on differentiation stage up to 25-fold) transcript abundance. No clear effect was observed for other MMPs, TIMP-1 or -2. The increase of MMP-1 and -3 was confirmed on the protein level. Stretching experiments performed in the presence of a specific inhibitor of extracellular signal-regulated kinase (ERK) showed a strong suppression of the stretch-induced increase in MMP-1 and -3. In conclusion, we show that MMP-1 and MMP-3 are mechanosensitive genes in mineralizing the human osteoblast, and that the mechano-induction of these genes is mediated via the ERK pathway. Our findings implicate that these MMPs are important factors in the mechanoregulation of bone turnover. With the ability to generate MMPs at highly stretched sites, osteoblasts can potantially direct osteoclasts to specific bone surface areas prepared for resorption.

Prediction of torsional failure in 22 cadaver femora with and without simulated subtrochanteric metastatic defects: a CT scan-based finite element analysis (Article)

2006-07-01T00:00:00Z

BACKGROUND: In metastatic bone disease, prophylactic fixation of impending long bone fracture is preferred over surgical treatment of a manifest fracture. There are no reliable guidelines for prediction of pathological fracture risk, however. We aimed to determine whether finite element (FE) models constructed from quantitative CT scans could be used for predicting pathological fracture load and location in a cadaver model of metastatic bone disease. MATERIAL AND METHODS: Subject-specific FE models were constructed from quantitative CT scans of 11 pairs of human femora. To simulate a metastatic defect, a transcortical hole was made in the subtrochanteric region in one femur of each pair. All femora were experimentally loaded in torsion until fracture. FE simulations of the experimental set-up were performed and torsional stiffness and strain energy density (SED) distribution were determined. RESULTS: In 15 of the 22 cases, locations of maximal SED fitted with the actual fracture locations. The calculated torsional stiffness of the entire femur combined with a criterion based on the local SED distribution in the FE model predicted 82% of the variance of the experimental torsional failure load. INTERPRETATION: In the future, CT scan-based FE analysis may provide a useful tool for identification of impending pathological fractures requiring prophylactic stabilization.

The use of micro-CT to study bone architecture dynamics noninvasively (Article)

2006-06-01T00:00:00Z

High-resolution micro-CT has become a standard tool in the evaluation of bone architecture. It has recently progressed from an invasive tool for bone specimens into an in vivo tool for small animals. The combination of novel sophisticated evaluation methods, such as registration (matching) of sequential scans and computer simulation models will further evolve in vivo micro-CT into an optimal tool for small animal phenotyping and contemporary approaches for drug discovery relating to the skeleton.

Bone loss dynamics result in trabecular alignment in aging and ovariectomized rats (Article)

2006-05-01T00:00:00Z

Because of the destructive nature of techniques used to measure bone morphometry, studies of architectural changes and bone loss have utilized cross-sectional study designs, with all its inherent limitations in nuances. Here, the results of a longitudinal study using in vivo micro-CT are presented elucidating the dynamics of bone loss and architectural adaptation in rat models of aging and postmenopausal bone loss. Using 3-D methodology, we observed the changes in bone architecture in the proximal tibia of normally aging and ovariectomized rats for 54 weeks. Spatial patterns in bone resorption were observed that were similar for both groups. Remaining trabeculae increased in thickness or were remodeled into new trabecular structures, especially in the ovariectomized animals. The combination of bone loss and bone formation resulted in alignment of trabeculae across the growth plate. Cortical modeling that was associated with growth continued after cessation of longitudinal growth in the ovariectomized animals, resulting in shape changes of the proximal tibia. The organized nature of the changes in bone architecture that occurred after ovariectomy and the high similarity with the changes observed in the normally aging animals, suggest that estrogen depletion resulted in an acceleration of a normal bone adaptation process. The observed aligning of trabeculae suggests regulation through mechanical loading.

Stress-concentrating effect of resorption lacunae in trabecular bone (Article)

2006-04-01T00:00:00Z

Analyses of the distributions of stress and strain within individual bone trabeculae have not yet been reported. In this study, four trabeculae were imaged and finite elements models were generated in an attempt to quantify the variability of stress/strain in real trabeculae. In three of these trabeculae, cavities were identified with depths comparable to values reported for resorption lacunae ( approximately 50 microm)-although we cannot be certain, it is most probable that they are indeed resorption lacunae. A tensile load was applied to each trabeculum to simulate physiological loading and to ensure that bending was minimized. The force carried by each trabecula was calculated from this value using the average cross sectional area of each trabecula. The analyses predict that very high stresses (>100 MPa) existed within bone trabecular tissue. Stress and strain distributions were highly heterogeneous in all cases, more so in trabeculae with the presumptive resorption lacunae where at least 30% of the tissue had a strain greater than 4000 micoepsilon in all cases. Stresses were elevated at the pit of the lacunae, and peak stress concentrations were located in the longitudinal direction ahead of the lacunae. Given these high strains, we suggest that microdamage is inevitable around resorption lacunae in trabecular bone, and may cause the bone multicellular unit to proceed to resorb a packet of bone in the trabeculum rather than just resorb whatever localized area was initially targeted.

Glucosamine decreases expression of anabolic and catabolic genes in human osteoarthritic cartilage explants (Article)

2006-03-01T00:00:00Z

OBJECTIVE: To investigate the effect of glucosamine (GlcN) in a human osteoarthritic explant model on expression of genes involved in anabolic and catabolic activities of chondrocytes. METHODS: Human osteoarthritic explants, obtained during knee arthroplasty surgery, were pre-cultured (3 days) and treated with glucosamine-hydrochloride (GlcN-HCl) or glucosamine-3-sulphate (GlcN-S) at 0.5mM and 5mM (4 days). RNA was isolated from the explants and real time RT-PCR was performed. Additionally, total matrix metalloproteinase (MMP) activity was measured in culture medium. RESULTS: Addition of 5mM GlcN led to significant down-regulation of aggrecan (2.65-7.73-fold) and collagen type II (7.75-22.17-fold) gene expression, indicating inhibited anabolic activity. Considering catabolic activities, 5mM GlcN significantly down-regulated aggrecanase-1 and MMP3 and 5mM GlcN-S additionally down-regulated aggrecanase-2 and tissue inhibitor of MMP gene expression significantly. Gene expression was not significantly altered by 0.5mM GlcN. Total MMP activity in culture medium was only significantly reduced after addition of 5mM GlcN-HCl. CONCLUSION: The effects of GlcN on gene expression in a human osteoarthritic explant model suggest that enzymatic breakdown of the extra-cellular matrix might be reduced by the addition of 5mM GlcN. Additionally, restoration of already damaged cartilage is not to be expected, because gene expression of anabolic genes is also down-regulated. We suggest that chondroprotective properties of GlcN in vivo may be based on inhibiting further degradation due to catabolic activities, rather than on the ability to rebuild cartilage.

Quantification of subchondral bone changes in a murine osteoarthritis model using micro-CT (Article)

2006-01-01T00:00:00Z

In the past few years there has been a considerable interest in the role of bone in osteoarthritis. Despite the increasing evidence of the involvement of bone in osteoarthritis, it remains very difficult to attribute the cause or effect of changes in subchondral bone to the process of osteoarthritis. Although osteoarthritis in mice provides a useful model to study changes in the subchondral bone, detailed quantification of these changes is lacking. Therefore, the goal of this study was to quantify subchondral bone changes in a murine osteoarthritis model by use of micro-computed tomography (micro-CT). We induced osteoarthritis-like characteristics in the knee joints of mice using collagenase injections, and after four weeks we calculated various 3D morphometric parameters in the epiphysis of the proximal tibia. The collagenase injections caused cartilage damage, visible in histological sections, particularly on the medial tibial plateau. Micro-CT analysis revealed that the thickness of the subchondral bone plate was decreased both at the lateral and the medial side. The trabecular compartment demonstrated a small but significant reduction in bone volume fraction compared to the contralateral control joints. Trabeculae in the collagenase-injected joints were thinner but their shape remained rod-like. Furthermore, the connectivity between trabeculae was reduced and the trabecular spacing was increased. In conclusion, four weeks after induction of osteoarthritis in the murine knee subtle but significant changes in subchondral bone architecture could be detected and quantified in 3D with micro-CT analysis.

Identification of acid-sensing ion channels in bone (Article)

2005-11-01T00:00:00Z

Bone balances serum pH variations and both osteoclasts and osteoblasts are regulated by subtle changes in pH. The aim of the current study was to identify molecules in bone that can sense pH. Interesting candidates are the acid-sensing ion channels (ASICs). In bone, ASIC2 and ASIC3 were most abundant, while in chondrocytes it was ASIC1. Isolated human monocytes expressed ASIC1, -2, and -3, which persisted after induction to osteoclast differentiation, albeit to a lower level. In human osteoblasts ASIC1, ASIC2, and ASIC3 mRNAs were shown. Western blot and immunostaining confirmed this at protein level. ASIC4 expression was always very low abundant. For the first time, we demonstrated ASICs in human skeleton, providing a means to sense and respond to differences in extracellular pH.

Hypervitaminosis D mediates compensatory Ca2+ hyperabsorption in TRPV5 knockout mice (Article)

2005-11-01T00:00:00Z

Vitamin D plays an important role in Ca(2+) homeostasis by controlling Ca(2+) (re)absorption in intestine, kidney, and bone. The epithelial Ca(2+) channel TRPV5 mediates the Ca(2+) entry step in active Ca(2+) reabsorption. TRPV5 knockout (TRPV5(-/-)) mice show impaired Ca(2+) reabsorption, hypercalciuria, hypervitaminosis D, and intestinal hyperabsorption of Ca(2+). Moreover, these mice demonstrate upregulation of intestinal TRPV6 and calbindin-D(9K) expression compared with wild-type mice. For addressing the role of the observed hypervitaminosis D in the maintenance of Ca(2+) homeostasis and the regulation of expression levels of the Ca(2+) transport proteins in kidney and intestine, TRPV5/25-hydroxyvitamin-D(3)-1alpha-hydroxylase double knockout (TRPV5(-/-)/1alpha-OHase(-/-)) mice, which show undetectable serum 1,25(OH)(2)D(3) levels, were generated. TRPV5(-/-)/1alpha-OHase(-/-) mice displayed a significant hypocalcemia compared with wild-type mice (1.10 +/- 0.02 and 2.54 +/- 0.01 mM, respectively; P < 0.05). mRNA levels of renal calbindin-D(28K) (7 +/- 2%), calbindin-D(9K) (32 +/- 4%), Na(+)/Ca(2+) exchanger (12 +/- 2%), and intestinal TRPV6 (40 +/- 8%) and calbindin-D(9K) (26 +/- 4%) expression levels were decreased compared with wild-type mice. Hyperparathyroidism and rickets were present in TRPV5(-/-)/1alpha-OHase(-/-) mice, more pronounced than observed in single TRPV5 or 1alpha-OHase knockout mice. It is interesting that a renal Ca(2+) leak, as demonstrated in TRPV5(-/-) mice, persisted in TRPV5(-/-)/1alpha-OHase(-/-) mice, but a compensatory upregulation of intestinal Ca(2+) transporters was abolished. In conclusion, the elevation of serum 1,25(OH)(2)D(3) levels in TRPV5(-/-) mice is responsible for the upregulation of intestinal Ca(2+) transporters and Ca(2+) hyperabsorption. Hypervitaminosis D, therefore, is of crucial importance to maintain normocalcemia in impaired Ca(2+) reabsorption in TRPV5(-/-) mice.

Longitudinal micro-CT scans to evaluate bone architecture (Article)

2005-10-01T00:00:00Z

Lordotic vertebrae in sea bass (Dicentrarchus labrax L.) are adapted to increased loads (Article)

2005-06-01T00:00:00Z

Lordosis in fish is an abnormal ventral curvature of the vertebral column, accompanied by abnormal calcification of the afflicted vertebrae. Incidences of lordosis are a major problem in aquaculture and often correlate with increased swimming activity. To understand the biomechanical causes and consequences of lordosis, we mapped the morphological changes that occur in the vertebrae of European sea bass during their development from larva to juvenile. Our micro-CT analysis of lordotic and non-lordotic vertebrae revealed significant differences in their micro-architecture. Lordotic vertebrae have a larger bone volume, flattened dorsal zygapophyses and extra lateral ridges. They also have a larger second moment of area (both lateral and dorso-ventral) than non-lordotic vertebrae. This morphology suggests lordotic vertebrae to be adapted to an increased bending moment, caused by the axial musculature during increased swimming activity. We hypothesize the increase in swimming activity to have a two-fold effect in animals that become lordotic. The first effect is buckling failure of the axial skeleton due to an increased compressive load. The second effect is extra bone deposition as an adaptive response of the vertebrae at the cellular level, caused by an increased strain and strain rate in these vertebrae. Lordosis thus comprises both a buckling failure of the vertebral column and a molecular response that adapts the lordotic vertebrae to a new loading regime.

The effect of glucosamine sulphate on osteoarthritis: design of a long- term randomised clinical trial [ISRCTN54513166]. (Article)

2005-04-26T00:00:00Z

BACKGROUND: Pharmacological treatment for osteoarthritis (OA) can be divided into two groups: symptom-modifying drugs and disease-modifying drugs. Symptom-modifying drugs are currently the prescription of choice for patients with OA, as disease-modifying drugs are not yet available in usual care. However, there has recently been a lot of debate about glucosamine sulphate (GS), a biological agent that is thought to have both symptom-modifying and disease-modifying properties. This assumption has yet to be proved. The objective of this article is to present the design of a blind randomised clinical trial that examines the long-term symptom-modifying and disease-modifying effectiveness of GS in patients with hip OA. This trial is ongoing and will finish in March 2006. METHODS/DESIGN: Patients with hip OA meeting the ACR-criteria are randomly allocated to either 1500 mg of oral GS or placebo for the duration of two years. The primary outcome measures, which are joint space narrowing (JSN), and change in the pain and function score of the Western Ontario McMaster Universities Osteoarthritis index (WOMAC), are determined at baseline and after two years of follow-up during the final assessment. Intermediate measures at three-month intervals throughout the trial are used to study secondary outcome measures. Secondary outcome measures are changes in WOMAC stiffness score, quality of life, medical consumption, side effects and differences in biomarker CTX-II.

An improved segmentation method for in vivo microCT imaging (Article)

2004-10-01T00:00:00Z

Image segmentation methods for microCT can influence the accuracy of bone morphometry calculations. A new automated segmentation method is introduced, and its performance is compared with standard segmentation methods. The new method can improve the results of in vivo microCT, where the need to keep radiation dose low limits scan quality. INTRODUCTION: An important topic for microCT analysis of bone samples is the segmentation of the original reconstructed grayscale data sets to separate bone from non-bone. Problems like noise, resolution limitations, and beam-hardening make this a nontrivial issue. Inappropriate segmentation methods will reduce the potential power of microCT and may introduce bias in the architectural measurements, in particular, when new in vivo microCT with its inherent limitations in scan quality is used. Here we introduce a new segmentation method using local thresholds and compare its performance to standard global segmentation methods. MATERIAL AND METHODS: The local threshold method was validated by comparing the result of the segmentation with histology. Furthermore, the effect of choosing this new method versus standard segmentation methods using global threshold values was investigated by studying the sensitivity of these methods to signal to noise ratio and resolution. RESULTS: Using the new method on high-quality scans yielded accurate results and virtually no differences between histology and the segmented data sets could be observed. When prior knowledge about the volume fraction of the bone was available the global threshold also resulted in appropriate results. Degrading the scan quality had only minor effects on the performance of the new segmentation method. Although global segmentation methods were not sensitive to noise, it was not possible to segment both lower mineralized thin trabeculae and the higher mineralized cortex correctly with the same threshold value. CONCLUSION: At high resolutions, both the new local and conventional global segmentation methods gave near exact representations of the bone structure. When scanned samples are not homogenous (e.g., thick cortices and thin trabeculae) and when resolution is relatively low, the local segmentation method outperforms global methods. It maximizes the potential of in vivo microCT by giving good structural representation without the need to use longer scanning times that would increase absorption of harmful X-ray radiation by the living tissue.

Stretch-induced phosphorylation of ERK1/2 depends on differentiation stage of osteoblasts (Article)

2004-10-01T00:00:00Z

The goal of this study was to investigate the effect of mechanical loading on osteoblasts and extracellular signal-regulated kinase (ERK1/2) signaling in relation to osteoblast differentiation and mineralization. A human osteoblast cell line (SV-HFO) was triggered to differentiate to the advanced state of mineralization by addition of the osteogenic factors dexamethasone and beta-glycerophosphate. Osteoblasts were subjected to cyclic, equibiaxial stretch for 5, 15, or 60 min at different stages of differentiation (days 7, 14, and 21). Baseline (static) phosphorylated ERK1/2 and total ERK1/2 levels gradually increased during osteoblast differentiation. Cyclic stretch induced a rapid increase in ERK1/2 phosphorylation with a maximum between 5 and 15 min. Prolonged stretching for 60 min resulted in a decrease of phosphorylated ERK1/2 towards baseline level, suggesting a desensitization mechanism. The effect of stretch on ERK1/2 phosphorylation was strongest at later stages of differentiation (days 14 and 21). At day 21, the increase of ERK1/2 phosphorylation in response to stretch was significantly lower in non-differentiating than in differentiating osteoblasts. This could not be explained by differences in cell density, but did correlate with the formation of extracellular matrix, collagen fibrils. Mineralization of the extracellular matrix did not lead to a further increase of ERK1/2 phosphorylation. In conclusion, the current study demonstrates that the extent of activation of the ERK1/2 pathway is dependent on the differentiation or functional stage of the osteoblast. The presence of an extracellular matrix, but not per se mineralization, seems to be the predominant determinant of osteoblastic response to strain.

Fibroblast growth factor-2 in serum-free medium is a potent mitogen and reduces dedifferentiation of human ear chondrocytes in monolayer culture (Article)

2004-07-01T00:00:00Z

The loss of the differentiated phenotype (dedifferentiation) during the expansion culture of donor chondrocytes remains a large problem in cartilage tissue engineering. Dedifferentiated chondrocytes produce other matrix components and therefore the tissue produced will be of less suitable quality. Previously, the addition of fibroblast growth factor-2 (FGF2) to a serum-containing medium (SCM) during expansion culture was shown to have positive effects on the phenotype of articular chondrocytes. In the present study, we focused on a more defined, serum-free medium (SFM), to expand chondrocytes in monolayer culture for the purpose of cartilage tissue engineering. Adult human ear chondrocytes were expanded in serum-free medium supplemented with 100 ng/ml FGF2. Expansion culture in a conventional serum-containing medium (10% FCS) served as control. The cell yield during expansion culture in serum-free medium with FGF2 was significantly higher compared to serum-containing medium. In addition, chondrocytes expanded in the serum-free medium with FGF2 expressed a more differentiated phenotype at the end of monolayer culture, as indicated by higher gene expression ratios of collagen type II to collagen type I and aggrecan to versican. Also, a higher gene expression of Sox9 was found. Next, suspension in alginate and subsequent culture in vitro or subcutaneous implantation in nude mice was used to evaluate the capacity of the chondrocytes, expanded in either medium, to re-express the differentiated phenotype (redifferentiation) and to form cartilage. The observed beneficial effects of the serum-free medium with FGF2 on the chondrocyte phenotype at the end of monolayer culture were sustained on both transcriptional and extracellular level throughout both redifferentiation methods.

The mechanical consequences of mineralization in embryonic bone (Article)

2004-07-01T00:00:00Z

The purpose of this study was to examine the effect of mineralization on the mechanical properties of embryonic bone rudiments. For this purpose, four-point bending experiments were performed on unmineralized and mineralized embryonic mouse ribs at 16 and 17 days of gestational age. Young's modulus was calculated using force-displacement data from the experiment in combination with finite element analysis (FEA). For the unmineralized specimens, a calculated average for the Young's modulus of 1.11 (+/- 0.62) MPa was established after corrections for sticking to the four-point bending device and aspect ratio, which is the ratio between the length of the bone and its diameter. For the mineralized specimens, the value was 117 (+/- 62) MPa after corrections. Hence, Young's moduli of embryonic bone rudiments increase by two orders of magnitude within 1 day, during endochondral ossification. As an effect, the hypertrophic chondrocytes in the calcifying cartilage experience a significant change in their mechanical environment. The chondrocytes are effectively stress shielded, which means that they do not carry stresses since stresses are supported by the stiffest parts of the tissue, which are in this case the diaphyseal cortex and the calcified matrix. The deformability of the hypertrophic chondrocytes is, therefore, severely reduced. Since the transition is so sudden and enormous, it can be seen as a process of 'catastrophic' proportion for the hypertrophic chondrocytes. The subsequent resorption of calcified cartilage and the expansion of the marrow cavity could be consequential to stress shielding.

Bisphosphonate treatment affects trabecular bone apparent modulus through micro-architecture rather than matrix properties (Article)

2004-05-01T00:00:00Z

Bisphosphonates are emerging as an important treatment for osteoporosis. But whether the reduced fracture risk associated with bisphosphonate treatment is due to increased bone mass, improved trabecular architecture and/or increased secondary mineralization of the calcified matrix remains unclear. We examined the effects of bisphosphonates on both the trabecular architecture and matrix properties of canine trabecular bone. Thirty-six beagles were divided into a control group and two treatment groups, one receiving risedronate and the other alendronate at 5-6 times the clinical dose for osteoporosis treatment. After one year, the dogs were killed, and samples from the first lumbar vertebrae were examined using a combination of micro-computed tomography, finite element modeling, and mechanical testing. By combining these methods, we examined the treatment effects on the calcified matrix and trabecular architecture independently. Conventional histomorphometry and microdamage data were obtained from the second and third lumbar vertebrae of the same dogs [Bone 28 (2001) 524]. Bisphosphonate treatment resulted in an increased apparent Young's modulus, decreased bone turnover, increased calcified matrix density, and increased microdamage. We could not detect any change in the effective Young's modulus of the calcified matrix in the bisphosphonate treated groups. The observed increase in apparent Young's modulus was due to increased bone mass and altered trabecular architecture rather than changes in the calcified matrix modulus. We hypothesize that the expected increase in the Young's modulus of the calcified matrix due to the increased calcified matrix density was counteracted by the accumulation of microdamage.

Altered tissue properties induce changes in cancellous bone architecture in aging and diseases (Article)

2004-03-01T00:00:00Z

The mechanical properties of cancellous bone depend on its architecture and the tissue properties of the mineralized matrix. The architecture is continuously adapted to external loads. In this paper, it was assumed that changes in tissue properties leading to changes in tissue deformation can induce adaptation of the architecture. We asked whether changes in cancellous bone architecture with aging and in e.g. early osteoarthrosis can be explained from changes in tissue properties.This was investigated using computer models in which the cancellous architecture was adapted to external loads. Bone tissue with deformations below a certain threshold was resorbed, deformations above another threshold induced formation. Deformations between these two boundaries, in the 'lazy zone', did not induce bone adaptation. The effects of changes in bone tissue stiffness on bone mass, global stiffness and architecture were investigated. The bone gain (40-60%) resulting from a 50% decrease in tissue stiffness (simulating diseased tissue) was much larger than the bone loss (2-30%) resulting from a 50% increase in tissue stiffness (simulating highly mineralized, old tissue). The adaptation induced by a decrease in tissue stiffness resulted in an almost constant stiffness in the main load bearing direction, but the transversal stiffness decreased. An increased tissue stiffness resulted in a higher stiffness in the main direction and overcompensation in the transversal directions: the global stiffness could become even smaller than the stiffness of the original model. Concluding, we showed that changes in trabecular bone in aging and diseases can be partly explained from changes in tissue properties.

The osteoporotic vertebral structure is well adapted to the loads of daily life, but not to infrequent "error" loads (Article)

2004-03-01T00:00:00Z

Osteoporotic vertebral fractures typically have a gradual onset, frequently remain clinically undetected, and do not seem to be related to traumatic events. The osteoporotic vertebrae may therefore be expected to display a less "optimal" bone architecture, leading to an uneven load distribution over the bone material. We evaluated the trabecular load distribution in an osteoporotic and a healthy vertebra under normal daily loading by combining three recent innovations: high resolution computed tomography (microCT) of entire bones, microfinite element analyses (microFEA), and parallel supercomputers. Much to our surprise, the number of highly loaded trabeculae was not higher in the osteoporotic vertebra than in the healthy one under normal daily loads (8% and 9%, respectively). The osteoporotic trabeculae were more oriented in the longitudinal direction, compensating for effects of bone loss and ensuring adequate stiffness for normal daily loading. The increased orientation did, however, make the osteoporotic structure less resistant against collateral "error" loads. In this case, the number of overloaded trabeculae in the osteoporotic vertebra was higher than in the healthy one (13% and 4%, respectively). These results strengthen the paradigm of a strong relationship between bone morphology and external loads applied during normal daily life. They also indicate that vertebral fractures result from actions like forward flexion or lifting, loads that may not be "daily" but are normally not traumatic either. If future clinical imaging techniques would enable such high-resolution images to be obtained in vivo, the combination of microCT and microFEA would produce a powerful tool to diagnose osteoporosis.

Detecting and tracking local changes in the tibiae of individual rats: a novel method to analyse longitudinal in vivo micro-CT data (Article)

2004-01-01T00:00:00Z

In this study we present the analysis of in vivo micro-CT scans using a new method based on image registration that accurately evaluates longitudinal micro-CT studies. We tested if detailed changes in the bone architecture could be detected and tracked in individual animals. A prototype in vivo micro-CT scanner (Skyscan 1076) was developed in which tibiae of rats that are lying on a bed under gas anaesthesia were scanned. For this study, three female Wistar rats were used: a sham-operated rat, an ovariectomised (OVX) rat and one rat that served as a reproducibility control. The reproducibility control rat was scanned twice in 1 day. The other animals were scanned at week 0, just before surgery, at week 4 and at week 14 after surgery. Architectural changes over time were detected by overlaying two data sets made at different time points using an algorithm that uses mutual information for optimal registration. The scans were segmented into binary data sets using a local thresholding algorithm. The reproducibility test showed small errors of less than 3% in bone volume measurements and errors less than 0.5% in measurements of trabecular thickness. The sham-operated rat showed no changes in total bone volume, though thinning and eventual loss of some small trabeculae could be detected, which could be related to the age of the animal. The OVX rat lost much trabecular bone volume, especially in the metaphysis (60% at week 4, 75% at week 14). The remaining trabeculae slowly increased in thickness. Following the different scans in time showed the forming of new trabecular structures. Additionally, small longitudinal growth at the growth plate could be detected after the first 4 weeks. Further, the OVX rat showed extensive modelling at the proximal endosteal lateral cortex. We have shown a new method that can detect and track changes in the local bone architecture and individual trabeculae in time, in an individual living animal. This method enables longitudinal in vivo micro-CT studies and has the potential to greatly contribute to experimental rat or mouse studies on pharmacological intervention and transgenic models.

Adaptation of subchondral bone in osteoarthritis (Article)

2004-01-01T00:00:00Z

Osteoarthritis is a chronic joint disease with pathological changes in the articulating cartilage and all other tissues that occupy the joint. Radin and coworkers have suggested the involvement of subchondral bone in the disease process. However, evidence for an essential role in the etiology has never been proven. Recent studies showing reduced chemical and mechanical properties of subchondral bone in various stages of the disease have invigorated interest in the role of subchondral bone in the development and progression of the disease. The current study showed that the concept of bone adaptation might explain subchondral stiffening, a process where subchondral bone becomes typically sclerotic in osteoarthritis. In addition, we report reduced mechanical matrix tissue properties as well as an increase in denatured collagen content. In conclusion, although osteoarthritic bone tissue contains increased denatured collagen and has reduced matrix mechanical properties, the widely accepted concept of subchondral stiffening is compatible with the process of normal bone adaptation.

Improved cartilage integration and interfacial strength after enzymatic treatment in a cartilage transplantation model (Article)

2004-01-01T00:00:00Z

The objective of the present study was to investigate whether treatment of articular cartilage with hyaluronidase and collagenase enhances histological and mechanical integration of a cartilage graft into a defect. Discs of 3 mm diameter were taken from 8-mm diameter bovine cartilage explants. Both discs and annulus were either treated for 24 hours with 0.1% hyaluronidase followed by 24 hours with 10 U/ml collagenase or left untreated (controls). Discs and annulus were reassembled and implanted subcutaneously in nude mice for 5 weeks. Integration of disc with surrounding cartilage was assessed histologically and tested biomechanically by performing a push-out test. After 5 weeks a significant increase in viable cell counts was seen in wound edges of the enzyme-treated group as compared with controls. Furthermore, matrix integration (expressed as a percentage of the total interface length that was connected; mean +/- standard error) was 83 +/- 15% in the treated samples versus 44 +/- 40% in the untreated controls. In the enzyme-treated group only, picro-Sirius Red staining revealed collagen crossing the interface perpendicular to the wound surface. Immunohistochemical analyses demonstrated that the interface tissue contained cartilage-specific collagen type II. Collagen type I was found only in a small region of fibrous tissue at the level of the superficial layer, and collagen type III was completely absent in both groups. A significant difference in interfacial strength was found using the push-out test: 1.32 +/- 0.15 MPa in the enzyme-treated group versus 0.84 +/- 0.14 MPa in the untreated controls. The study shows that enzyme treatment of cartilage wounds increases histological integration and improves biomechanical bonding strength. Enzymatic treatment may represent a promising addition to current techniques for articular cartilage repair.

Living cells in 1 of 2 frozen femoral heads (Article)

2003-12-01T00:00:00Z

Allogeneic, frozen bone is now the most commonly grafted tissue (Norman-Taylor and Villar 1997). Tissue banks collect bone material according to protocols developed with the aim of maintaining osseoinductive properties of grafts as well as preventing transmission of viral or bacterial diseases (Standards from the American Association of Tissue Banks (AATB) or from the European Association for Musculo-skeletal Transplanting (EAMST)). Standard procedures include cryopreservation of tissue at -80 degrees C, which is generally considered to devitalize the bone by killing all cells present, resulting in reduced immunogenicity of the graft. The osseoinductive properties of frozen, allogeneic bone grafts have therefore mainly been attributed to the dead bone matrix, that may provide osteoblast-stimulating growth factors and other essential proteins, and/or an osteoclast substrate to direct bone remodeling (Aspenberg et al. 1996, Kingsmill et al. 1999). Recently however, it was suggested that some cells in bone biopsies may survive standard bone bank freezing procotols. It is unclear whether vital cells are present in other bone banks and whether these cells can contribute to the clinical outcome of frozen allogeneic bone grafting. In this report, we show that frozen bone biopsies, obtained from the Erasmus Medical Center bone bank may contain living cells that can be cultured in vitro. These cultured cells were found to originate from the donor by genotyping.

The dependence of the elastic properties of osteoporotic cancellous bone on volume fraction and fabric (Article)

2003-10-01T00:00:00Z

Osteoporosis is a progressive systemic skeletal condition characterized by low bone mass and microarchitectural deterioration, with a consequent increase in susceptibility to fracture. Hence, osteoporosis would be best diagnosed by in vivo measurements of bone strength. As this is not clinically feasible, our goal is to estimate bone strength through the assessment of elastic properties, which are highly correlated to strength. Previously established relations between morphological parameters (volume fraction and fabric) and elastic constants could be applied to estimate cancellous bone stiffness in vivo. However, these relations were determined for normal cancellous bone. Cancellous bone from osteoporotic patients may require different relations. In this study we set out to answer two questions. First, can the elastic properties of osteoporotic cancellous bone be estimated from morphological parameters? Second, do the relations between morphological parameters and elastic constants, determined for normal bone, apply to osteoporotic bone as well? To answer these questions we used cancellous bone cubes from femoral heads of patients with (n=26) and without (n=32) hip fractures. The elastic properties of the cubes were determined using micro-finite element analysis, assuming equal tissue moduli for all specimens. The morphological parameters were determined using microcomputed tomography. Our results showed that, for equal tissue properties, the elastic properties of cancellous bone from fracture patients could indeed be estimated from morphological parameters. The morphology-based relations used to estimate the elastic properties of cancellous bone are not different for women with or without fractures.

A simulation model at trabecular level to predict effects of antiresorptive treatment after menopause (Article)

2003-09-23T00:00:00Z

Antiresorptive drugs are widely used to prevent osteoporotic fractures in men and women. Large clinical trials have shown vertebral fracture risk reductions up to 50%, resulting from relatively small increases of 3-8% in bone mineral density (BMD). We developed a computer model that mimics bone turnover in human vertebral cancellous bone during menopause and antiresorptive treatment. This model links cell activity in trabeculae to changes in bone volume and mechanical properties. We asked whether treatment started shortly after menopause is better than treatment started late after menopause. In order to answer this question we used the model to simulate menopause and 5 years of anti-resorptive treatment with two different agents: one incorporated in the tissue, one not incorporated. We found that late treatment can result in almost the same bone mass as early treatment, but early treatment is much better in conserving the strength and stiffness of the cancellous bone. The effect of the incorporation of drugs in the tissue (giving the drugs a long half-life) was small. After discontinuation of treatment, bone was lost slower, but after 20 years the difference between the incorporated and the not incorporated drug in stiffness and bone volume was below 3%. This kind of simulation model may be used to preclinically test new pharmaceuticals and treatment protocols and to predict long-term effects of treatment before patient data become available.

Canine cancellous bone microarchitecture after one year of high-dose bisphosphonates (Article)

2003-04-03T00:00:00Z

We examined the effects of one-year high-dose bisphosphonates (risedronate 0.5 mg/kg/day or alendronate 1.0 mg/kg/day) on the three-dimensional (3-D) microstructural and mechanical properties of canine cancellous bone. A high-resolution micro-CT scanner was used to scan cubic specimens produced from the first lumbar vertebrae. Microstructural properties of the specimens were calculated directly from the 3-D datasets and the mechanical properties of the specimens were determined. Our data demonstrate significant microarchitectural changes in the bisphosphonate-treated cancellous bone that was typically plate-like, denser, with thicker and more trabeculae compared with those of the controls. Consistent with architectural changes, the Young's moduli of cancellous bone increased in all three directions with the greatest increase in primary axial loading (cephalo-caudal) direction after treatment. Our results suggest a bone remodeling-adaptation mechanism stimulated by bisphosphonates that increases bone volume fraction, thickens trabeculae, changes trabeculae towards more plate-like, and increases mechanical properties. The secondary degree of anisotropy contributed significantly to the explained variance in bone strength, and the primary or tertiary degree of anisotropy improved the explanation of variances for Young's moduli, i.e., 79% of strength variances or 74-83% of modulus variances could be explained by the combined anisotropy and bone volume fraction. These significant improvements of cancellous bone architecture provide a rationale for the clinical observation that fracture risk decreased by 50% in the first year of bisphosphonate therapy with only a 5% increase in bone mineral density. We conclude that bisphosphonates enhance mechanical properties and reduce fracture risk by improving architectural anisotropy of cancellous bone 3-D microarchitecture.

Mechanical control of human osteoblast apoptosis and proliferation in relation to differentiation (Article)

2003-04-01T00:00:00Z

Bone cells respond to mechanical stimulation. This is thought to be the mechanism by which bone adapts to mechanical loading. Reported responses of bone cells to mechanical stimuli vary widely and therefore there is no consensus on what mechanisms of mechanotransduction are physiologically relevant. We hypothesize that the differentiation stage of osteoblastic cells used to study responses to strain in vitro determines the outcome of applied loading. A human fetal osteoblast cell line was triggered to differentiate in culture to the advanced state of mineralization by addition of the osteogenic factors dexamethasone and b-glycerophosphate. Osteoblast cultures were subjected to increasing levels of cyclic, equibiaxial stretch at different stages of differentiation. We show that differentiation of human osteoblasts affects their responses to stretch in vitro. In 7-day osteoblast cultures, stretch results in decreased cell numbers as cells are triggered into apoptosis, independent of the stretch level (between 0.4-2.5%). In more mature cultures, apoptosis is not affected by the same treatment. Stretching differentiating cultures at day 14 actually increases proliferation. This is the first study reporting on differentiation-dependent mechanical control of osteoblast proliferation and apoptosis and is fundamental in understanding mechanotransduction processes in bone. The tight regulation of these responses by differentiation implies the significance of the differentiation stage of osteoblasts for the translation of mechanical signals and corroborates with the putative role of the osteoblastic lineage as mechanotransducer in bone.

ERK activation and alpha v beta 3 integrin signaling through Shc recruitment in response to mechanical stimulation in human osteoblasts (Article)

2002-09-12T00:00:00Z

Osteoblast growth and differentiation are critical processes for bone development and maintenance, and are regulated by both humoral and mechanical factors. Humoral (hormonal) factors can affect gene transcription via MAPkinases, e.g., extracellular signal-regulated kinase (ERK). We studied whether the ERK pathway is also involved in processing mechanical inputs in human bone cells. Exposing MG63 cells to physiologically relevant levels of fluid flow resulted in ERK phosphorylation. Genistein blocked this response, indicating that it is dependent on tyrosine phosphorylation. Furthermore, alpha v beta 3 integrins were activated in response to fluid flow, as shown by recruitment of adaptor molecule Shc and clustering of alpha v beta 3 in focal adhesion-like structures. Antibodies blocking formation of beta 1 or beta 3 integrin-matrix interactions or RGD peptides could not inhibit fluid flow-induced ERK phosphorylation, suggesting that formation of new integrin-matrix interactions is not essential for this response and that other upstream mechanosensors regulate induction of ERK phosphorylation in response to fluid flow in human bone cells.

Cancellous bone mechanical properties from normals and patients with hip fractures differ on the structure level, not on the bone hard tissue level (Article)

2002-05-01T00:00:00Z

Osteoporosis is currently defined in terms of low bone mass. However, the source of fragility leading to fracture has not been adequately described. In particular, the contributions of bone tissue properties and architecture to the risk or incidence of fracture are poorly understood. In an earlier experimental study, it was found that the architectural anisotropy of cancellous bone from the femoral heads of fracture patients was significantly increased compared with age- and density-matched control material (Ciarelli et al., J Bone Miner Res 15:32-40; 2000). Using a combination of compression testing and micro-finite element analysis on a subset of cancellous bone specimens from that study, we calculated the hard tissue mechanical properties and the apparent (macroscopic) mechanical properties. The tissue modulus was 10.0 GPa (SD 2.2) for the control group and 10.8 GPa (SD 3.3) for the fracture group (not significant). There were no differences in either the apparent yield strains, percentages of highly strained tissue, or the relationship between apparent yield stress and apparent elastic modulus. Hence, a difference in the tissue yield properties is unlikely. At the apparent level, the fracture group had a significantly decreased transverse stiffness, resulting in increased mechanical anisotropy. These changes suggest that bone in the fracture group was "overadapted" to the primary load axis, at the cost of fragility in the transverse direction. We conclude that individuals with a history of osteoporotic fractures do not have weaker bone tissue. Architectural and mechanical anisotropy alone renders their bone weaker in the nonprimary loading direction.

Suitability of texture features to assess changes in trabecular bone architecture (Article)

2002-03-19T00:00:00Z

Cell and nucleus deformation in compressed chondrocyte-alginate constructs: temporal changes and calculation of cell modulus (Article)

2002-02-15T00:00:00Z

Mechanical loading is essential for the homeostasis of articular cartilage and may be necessary for achieving functional tissue engineered cartilage repair using isolated cells seeded in scaffolds such as alginate. Chondrocyte mechanotransduction is poorly understood, but may involve cell deformation and associated distortion of intracellular organelles. The present study used confocal microscopy to examine cell and nucleus morphology in isolated chondrocytes compressed in alginate constructs. Compression of 2% alginate resulted in cell deformation from a spherical to an oblate ellipsoid morphology with conservation of cell volume. Cell deformation was associated with deformation, to a lesser degree, of the nucleus. Despite constant cell deformation over a 25 min period of static compression, the nucleus deformation reduced significantly, particularly in the axis perpendicular to the applied compression. Constructs made of a lower alginate concentration exhibited a reduced compressive modulus with an altered cellular response to compression. In 1.2% alginate, compression resulted in cell deformation which was initially of a similar magnitude to that in 2% alginate but subsequently reduced over a 60 min period reflecting the viscoelastic behaviour of the gel. This phenomenon enabled the calculation of a stress-strain relationship for the cell with an estimated Young's modulus value of approx. 3 kPa.

Architectural changes independent of bone mineral in osteoporosis (Article)

2002-01-01T00:00:00Z

Trabecular bone's mechanical properties are affected by its non-uniform mineral distribution (Article)

2001-12-01T00:00:00Z

The bone remodeling process takes place at the surface of trabeculae and results in a non-uniform mineral distribution. This will affect the mechanical properties of cancellous bone, because the properties of bone tissue depend on its mineral content. We investigated how large this effect is by simulating several non-uniform mineral distributions in 3D finite element models of human trabecular bone and calculating the apparent stiffness of these models. In the 'linear model' we assumed a linear relation between mineral content and Young's modulus of the tissue. In the 'exponential model' we included an empirical exponential relation in the model. When the linear model was used the mineral distribution slightly changed the apparent stiffness, the difference varied between an 8% decrease and a 4% increase compared to the uniform model with the same BMD. The exponential model resulted in up to 20% increased apparent stiffness in the main load-bearing direction. A thin less mineralized surface layer (28 microm) and highly mineralized interstitial bone (mimicking mineralization resulting from anti-resorptive treatment) resulted in the highest stiffness. This could explain large reductions in fracture risk resulting from small increases in BMD. The non-uniform mineral distribution could also explain why bone tissue stiffness determined using nano-indentation is usually higher than finite element (FE)-determined stiffness. We conclude that the non-uniform mineral distribution in trabeculae does affect the mechanical properties of cancellous bone and that the tissue stiffness determined using FE-modeling could be improved by including detailed information about mineral distribution in trabeculae in the models.

A decreased subchondral trabecular bone tissue elastic modulus is associated with pre-arthritic cartilage damage (Article)

2001-09-11T00:00:00Z

In osteoarthritis, one postulate is that changes in the mechanical properties of the subchondral bone layer result in cartilage damage. The goal of this study was to examine changes in subchondral trabecular bone properties at the calcified tissue level in the early stages of cartilage damage. Finite element models were constructed from microCT scans of trabectilar bone from the proximal tibia of donors with mild cartilage damage and from normal donors. In the donors with cartilage damage, macroscopic damage was present only in the medial compartment. The effective tissue elastic moduli were determined using a combination of finite element models and mechanical testing. The bone tissue modulus was reduced by 60% in the medial condyle of the cases with cartilage damage compared to the control specimens. Neither the presence of cartilage damage nor the anatomic site (medial vs. lateral) affected the elastic modulus at the apparent level. The volume fraction of trabecular bone was higher in the medial compartment compared to the lateral compartment of tibiae with cartilage damage (but not the controls), suggesting that mechanical properties were preserved in part at the apparent level by an increase in the bone volume fraction. It seems likely that the normal equilibrium between cartilage properties, bone tissue properties and bone volume fraction is disrupted early in the development of osteoarthritis.

Osteoporosis changes the amount of vertebral trabecular bone at risk of fracture but not the vertebral load distribution (Article)

2001-07-01T00:00:00Z

STUDY DESIGN: A finite-element study to investigate the amount of trabecular bone at risk of fracture and the distribution of load between trabecular core and cortical shell, for healthy, osteopenic, and osteoporotic vertebrae. OBJECTIVES: To determine differences between health y, osteopenic, and osteoporotic vertebrae with regard to the risk of fracture and the load distribution. SUMMARY OF BACKGROUND DATA: The literature contains no reports on the effects of osteopenia and osteoporosis on load distribution in vertebral bodies, nor any reports on the amount of trabecular bone at risk of fracture. METHODS: Computed tomography data of vertebral bodies were used to construct patient-specific finite-element models. These models were then used in finite-element analyses to determine the physiologic stresses and strains in the vertebrae. RESULTS: For all three classes of vertebrae the contribution of the trabecular core to the total load transfer decreased from about 70% near the endplates to about 50% in the midtransverse region. The amount of trabecular bone that is at risk of fracture was about 1% for healthy vertebrae, about 3% for osteopenic vertebrae, and about 16% for osteoporotic vertebrae. CONCLUSIONS: Our finite-element models indicated that neither osteopenia nor osteoporosis had any effect on the contribution of the trabecular core to the total load placed on the vertebra. The trabecular core carried about half the load. Our finite-element models indicated that osteoporosis had a significant effect on the amount of trabecular bone at risk of fracture, which increased from about 1% in healthy vertebrae to about 16% for osteoporotic vertebrae.

A three-dimensional simulation of age-related remodeling in trabecular bone (Article)

2001-04-01T00:00:00Z

After peak bone mass has been reached, the bone remodeling process results in a decrease in bone mass and strength. The formation deficit, the deficit of bone formation compared with previous resorption, results in bone loss. Moreover, trabeculae disconnected by resorption cavities probably are not repaired. The contributions of these mechanisms to the total bone loss are unclear. To investigate these contributions and the concomitant changes in trabecular architecture and mechanical properties, we made a computer simulation model of bone remodeling using microcomputed tomography (micro-CT) scans of human vertebral trabecular bone specimens. Up to 50 years of physiological remodeling were simulated. Resorption cavities were created and refilled 3 months later. These cavities were not refilled completely, to simulate the formation deficit. Disconnected trabeculae were not repaired; loose fragments generated during the simulation were removed. Resorption depth, formation deficit, and remodeling space were based on biological data. The rate of bone loss varied between 0.3% and 1.1% per year. Stiffness anisotropy increased, and morphological anisotropy (mean intercept length [MIL]) was almost unaffected. Connectivity density increased or decreased, depending on the remodeling parameters. The formation deficit accounted for 69-95%, disconnected trabeculae for 1-21%, and loose fragments for 1-17% of the bone loss. Increasing formation deficit from 1.8% to 5.4% tripled bone loss but only doubled the decrease in stiffness. Increasing resorption depth from 28 to 56 microm slightly increased bone loss but drastically decreased stiffness. Decreasing the formation deficit helps to prevent bone loss, but reducing resorption depth is more effective in preventing loss of mechanical stiffness.

Introduction and evaluation of a gray-value voxel conversion technique (Article)

2001-04-01T00:00:00Z

In micro finite element analyses (microFEA) of cancellous bone, the 3D-imaging data that the FEA-models are based on, contain a range of gray-values. In the construction of the eventual FEA-model, these gray-values are commonly thresholded. Although thresholding is successful at small voxel sizes, at larger voxel sizes there is substantial loss of trabecular connectivity. We propose a new method: the gray-value method, where the microFEA-models use the information within the 3D-imaging data directly, without prior thresholding. Our question was twofold. First, how does the gray-value method compare to both plain and mass-compensated thresholding? Second, what is the effect of element size on the results obtained with the gray-value method? We used nine microCT-scans of human vertebral cancellous bone. These were degraded to represent different resolutions, and converted into microFEA-models using plain thresholding, mass-compensated thresholding, and the gray-value method. The apparent elastic moduli of the specimens were determined using microFEA. The different methods were compared on the basis of the apparent elastic moduli, compared to those calculated for a 28 microm reference model. The results showed that the gray-value method greatly improves the results relative to other methods. The gray-value method gives accurate predictions of the apparent elastic moduli, for voxel sizes up to one trabecular thickness (Tb.Th.). For voxel sizes greater than one Tb.Th. the accuracy, although still better than for both thresholding methods, becomes increasingly worse.

Mechanical consequences of bone loss in cancellous bone (Article)

2001-03-01T00:00:00Z

The skeleton is continuously being renewed in the bone remodeling process. This prevents accumulation of damage and adapts the architecture to external loads. A side effect is a gradual decrease of bone mass, strength, and stiffness with age. We investigated the effects of bone loss on the load distribution and mechanical properties of cancellous bone using three-dimensional (3D) computer models. Several bone loss scenarios were simulated. Bone matrix was removed at locations of high strain, of low strain, and random throughout the architecture. Furthermore, resorption cavities and thinning of trabeculae were simulated. Removal of 7% of the bone mass at highly strained locations had deleterious effects on the mechanical properties, while up to 50% of the bone volume could be removed at locations of low strain. Thus, if remodeling would be initiated only at highly strained locations, where repair is likely needed, cancellous bone would be continuously at risk of fracture. Thinning of trabeculae resulted in relatively small decreases in stiffness; the same bone loss caused by resorption cavities caused large decreases in stiffness and high strain peaks at the bottom of the cavities. This explains that a reduction in the number and size of resorption cavities in antiresorptive drug treatment can result in large reductions in fracture risk, with small increases in bone mass. Strains in trabeculae surrounding a cavity increased by up to 1,000 microstrains, which could lead to bone apposition. These results give insight in the mechanical effects of bone remodeling and resorption at trabecular level.

Parallel plate model for trabecular bone exhibits volume fraction-dependent bias (Article)

2000-11-01T00:00:00Z

Unbiased stereological methods were used in conjunction with microcomputed tomographic (micro-CT) scans of human and animal bone to investigate errors created when the parallel plate model was used to calculate morphometric parameters. Bone samples were obtained from the human proximal tibia, canine distal femur, rat tail, and pig spine and scanned in a micro-CT scanner. Trabecular thickness, trabecular spacing, and trabecular number were calculated using the parallel plate model. Direct thickness, and spacing and connectivity density were calculated using unbiased three-dimensional methods. Both thickness and spacing calculated using the plate model were well correlated to the direct three-dimensional measures (r(2) = 0. 77-0.92). The correlation between trabecular number and connectivity density varied greatly (r(2) = 0.41-0.94). Whereas trabecular thickness was consistently underestimated using the plate model, trabecular spacing was underestimated at low volume fractions and overestimated at high volume fractions. Use of the plate model resulted in a volume-dependent bias in measures of thickness and spacing (p < 0.001). This was a result of the fact that samples of low volume fraction were much more "rod-like" than those of the higher volume fraction. Our findings indicate that the plate model provides biased results, especially when populations with different volume fractions are compared. Therefore, we recommend direct thickness measures when three-dimensional data sets are available.

Monitoring water content in deforming intervertebral disc tissue by finite element analysis of MRI data (Article)

2000-10-01T00:00:00Z

Mechanical loading, occurring during normal daily life, causes fluid to be expelled from intervertebral discs. Excessive fluid loss during heavy loading might make the disc more vulnerable to damage. In this study, fluid loss was investigated in vitro through monitoring the loss of MRI signal intensity in four bovine coccygeal intervertebral discs, compressed at 2000 N during 1.5 hr. The MRI signals were analyzed with the aid of finite element models to account for the deformation of the tissue. A gradual signal loss over time was found during loading, the most pronounced loss occurring in the central disc region. Initial patterns of signal distribution were quite variable between specimens but repeatable within specimens.

Sensitivity of periprosthetic stress-shielding to load and the bone density-modulus relationship in subject-specific finite element models (Article)

2000-07-01T00:00:00Z

Subject-specific finite element (FE) computer models of the proximal femur in hip replacement could potentially predict stress-shielding and subsequent bone loss in individual patients. Before such predictions can be made, it is important first to determine if between subject differences in stress-shielding are sensitive to poorly defined parameters such as the load and the bone material properties. In this study we investigate if subject-specific FE models provide consistent stress-shielding patterns in the bone, independent of the choice of the loading conditions and the bone density-modulus relationship used in the computer model. FE models of two right canine femurs with and without implants were constructed based on contiguous computed tomography (CT) scans so that subject-specific estimates of stress-shielding could be calculated. Four different loading conditions and two bone density-modulus relationships were tested. Stress-shielding was defined as the decrease of strain energy per gram bone mass in the femur with the implant in place relative to the intact femur.The analyses showed that for the four loading conditions and two bone density-modulus relationships the difference in stress-shielding between the two subjects was essentially constant (1% variation) when the same loading condition and density-modulus relationship was used for both subjects. The severity of stress-shielding within a subject was sensitive to these input parameters, varying up to 20% in specific regions with a change in loading conditions and up to 10% for a change in the assumed density-modulus relationship. We conclude that although the choice of input parameters can substantially affect stress-shielding in an individual, this choice had virtually no effect on the relative differences in femoral periprosthetic stress-shielding between individuals. Thus, while care should be taken in the interpretation of the absolute value of stress-shielding calculated with these type of models, subject-specific FE models may be useful for explaining the variation in bone adaptation responsiveness between different subjects in experimental or clinical studies.

Finite element analysis of trabecular bone structure: a comparison of image-based meshing techniques (Article)

1998-12-01T00:00:00Z

In this study, we investigate if finite element (FE) analyses of human trabecular bone architecture based on 168 microm images can provide relevant information about the bone mechanical characteristics. Three human trabecular bone samples, one taken from the femoral head, one from the iliac crest, and one from the lumbar spine, were imaged with micro-computed tomography (micro-CT) using a 28 microm resolution. After reconstruction the resolution was coarsened to 168 microm. First, all reconstructions were thresholded and directly converted to FE-models built of hexahedral elements. For the coarser resolutions of two samples, this resulted in a loss of trabecular connections and a subsequent loss of stiffness. To reduce this effect, a tetrahedral element meshing based on the marching cubes algorithm, as well as a modified hexahedron meshing, which thresholds the image such that load carrying bone mass is preserved, were employed. For each sample elastic moduli and tissue Von Mises stresses of the three different 168 microm models were compared to those from the hexahedron 28 microm model. For one sample the hexahedron meshing at 168 microm produced excellent results. For the other two samples the results obtained from the hexahedral models at 168 microm resolution were poor. Considerably better results were attained for these samples when using the mass-compensated or tetrahedron meshing techniques. We conclude that the accuracy of the FE-models at 168 microm strongly depends on the bone morphology, in particular its trabecular thickness. A substantial loss of trabecular connections during the hexahedron meshing process indicates that poor FE results will be obtained. In this case the tetrahedron or mass-compensated hexahedron meshing techniques can reduce the loss of connections and produce better results than the plain hexahedron meshing techniques.

Finite element aided tracking of signal intensity changes in deforming intervertebral disc tissue (Article)

1998-01-01T00:00:00Z

Tracking of signal intensity changes in soft tissue over time is often hampered by deformation of the tissue. In this study a method is described that uses finite element modeling to compensate for tissue deformation. The method is applied to the quantification of fluid redistribution in an intervertebral disc that deforms under mechanical load. The clinical importance of this application emerges from the increased susceptibility of the intervertebral disc to damage after a period of mechanical loading. The study shows that the use of the finite element aided approach results in a detailed map of tissue MRI signal changes, where the distorting effects of tissue deformation are eliminated.

Nondestructive measurements of implant-bone interface shear modulus and effects of implant geometry in pull-out tests (Article)

1997-03-01T00:00:00Z

Push-out and pull-out tests are used for destructive evaluation of implant-bone interface strength. Because nondestructive mechanical tests would allow maintenance of an intact interface for subsequent morphological study, we developed such a test to determine the shear modulus of the interface by measuring the shear deformation of a thin layer adjacent to the implant. A polyurethane foam model was used to test the experimental setup on a group of nine cylindrical implants with three different lengths (15-48 mm) and three different diameters (5-9.7 mm). The shear modulus of the interface, as calculated from the pull-out test, was validated against the shear modulus of the foam derived from tensile tests. The two values of shear modulus were well correlated (R2 = 0.8, p < 0.001), thus encouraging further application of the setup for tests of implant-bone interface mechanics. In addition, we also examined the effects of implant length and diameter. The length of the implants had a significant influence on the interface shear modulus (p < 0.05), indicating that comparisons of the variable should only be made of implants with the same length. The length and diameter of the implants were not critical parameters for the ultimate fixation strength.

Computational strategies for iterative solutions of large fem applications employing voxel data (Article)

1996-01-01T00:00:00Z

FE-models for structural solid mechanics analyses can be readily generated from computer images via a 'voxel convesion' method, whereby voxels in a two- or three-dimesional computer image are directly translated to elements in a FE-model. The fact that all elements thus generated are the same creates the possibilities for fast solution algorithm that can compensate for a large number of element. The solving methods described in this paper are based on an iterative solving algorithm in combination with a uniqueelement Element-by-Element (EBE) or with a newly developed Row-by-Row (RBR) matrix-vector multiplication strategy. With these methods it is possible to solve FE-models on the order of 105 3-D brick elements on a workstation and on the order of 106 elements on a Cray computer. The methods are demonstrated for the Boussinesq problem and for FF models that represent a porous trabecular bone structure The results show that the RBR method can be 3.2 times faster than the EBE method. It was concluded that the voxel conversion method in combination with these solving methods not only provides a powerful tool to analyse structures that can not be analysed in another way, but also that this approach can be competitive with traditional meshing and solving techniques.

Reconstruction of bone loading conditions from in vivo strain measurements (Article)

1995-06-01T00:00:00Z

A method is described whereby bone loading conditions can be reconstructed from in vivo strain measurements. The method uses ex vivo calibration measurements to find the relationship between the strain data and the loads applied to the bone. Using singular value decomposition, a transformation matrix is determined which provides the best linear relationship available between the measured strain data and the measured loading components in the calibration measurements. The transformation matrix can then be used to calculate the loads which correspond best with any given strain data set made with that specific bone and strain gages. In this manner, the applied loads of earlier performed in vivo strain measurements can be reconstructed. The method was tested for the reconstruction of the loads on a tibia of a goat. After determining the transformation matrix from a set of calibration measurements, the transformation matrix was used to reconstruct all loading components (three forces and three moments) of a set of test measurements whereby the applied loads were measured. It was found that the axial force and the torsional moment on the bone could be reproduced very accurately, showing a root mean square error (RMSE) of only 2% of the maximal load in the test. The reconstruction of the bending moments was slightly worse, showing a RMSE of 5-8% of the maximal moments. The reconstruction of the transverse force components proved less accurate and a RMSE up to 24% of the maximum was found. Accuracy can be improved by using weight factors for the loading conditions and a more accurate measurement of the location of the loads during the calibration measurements.

A new method to determine trabecular bone elastic properties and loading using micromechanical finite-element models (Article)

1995-01-01T00:00:00Z

The apparent mechanical behavior of trabecular bone depends on properties at the tissue or trabecular level. Many investigators have attempted to determine trabecular tissue properties and loading. However, accuracy and applicability of all methods reported are limited. The small size of the trabeculae and a possible size effect are complicating factors when using traditional testing methods on single trabeculae. Other methods reported, using models that describe the trabecular structure, are of limited value because they consider bone as a repetitive structure in order to describe a reasonably large region of bone. The present study introduces a new finite-element method strategy that enables analysis of reasonably large regions of trabecular bone in full detail. The method uses three-dimensional serial reconstruction techniques to construct a large-scale FE model, by directly converting voxels to elements. A 5 mm cube of trabecular bone was modeled in this way, resulting in a FE model that consists of 296,679 elements. Special strategies were developed to solve the set of equations that results from the FE approach. Using this model in combination with experimental apparent data taken from the literature, the upper and lower boundaries for the tissue modulus were calculated to be 10.1 and 2.23 GPa, respectively. From the local stress and strain distributions it was concluded that the deformation mode of the trabeculae in the present cube was predominantly in bending. It was concluded that the method developed offers new perspectives for the study of trabecular bone.

Quantitative analysis of bone reactions to relative motions at implant-bone interfaces (Article)

1993-11-01T00:00:00Z

Connective soft tissues at the interface between implants and bone, such as in human joint replacements, can endanger the stability of the implant fixation. The potential of an implant to generate interface bone resorption and form soft tissue depends on many variables, including mechanical ones. These mechanical factors can be expressed in terms of relative motions between bone and implant at the interface or deformation of the interfacial material. The purpose of this investigation was to determine if interface debonding and subsequent relative interface motions can be responsible for interface degradation and soft tissue interposition as seen in experiments and clinical results. A finite element computer program was augmented with a mathematical description of interface debonding, dependent on interface stress criteria, and soft tissue interface interposition, dependent on relative interface motions. Three simplified models of orthopaedic implants were constructed: a cortical bone screw for fracture fixation plates, a femoral resurfacing prosthesis and a straight stem model, cemented in a bone. The predicted computer configurations were compared with clinical observations. The computer results showed how interface disruption and fibrous tissue interposition interrelate and possibly enhance each other, whereby a progressive development of the soft tissue layer can occur. Around the cortical bone screw, the predicted resorption patterns were relatively large directly under the screw head and showed a pivot point in the opposite cortex. The resurfacing cup model predicted some fibrous tissue formation under the medial and lateral cup rim, whereby the medial layer developed first because of higher initial interface stresses. The straight stem model predicted initial interface failure at the proximal parts. After proximal resorption and fibrous tissue interposition, the medial interface was completely disrupted and developed an interface layer. The distal and mid lateral side maintained within the strength criterion. Although the applied models were relatively simple, the results showed reasonable qualitative agreement with resorption patterns found in clinical studies concerning bone screws and the resurfacing cup. The hypothesis that interface debonding and subsequent relative (micro)motions could be responsible for bone resorption and fibrous tissue propagation is thereby sustained by the results.

The behavior of adaptive bone-remodeling simulation models (Article)

1992-12-01T00:00:00Z

The process of adaptive bone remodeling can be described mathematically and simulated in a computer model, integrated with the finite element method. In the model discussed here, cortical and trabecular bone are described as continuous materials with variable density. The remodeling rule applied to simulate the remodeling process in each element individually is, in fact, an objective function for an optimization process, relative to the external load. Its purpose is to obtain a constant, preset value for the strain energy per unit bone mass, by adapting the density. If an element in the structure cannot achieve that, it either turns to its maximal density (cortical bone) or resorbs completely. It is found that the solution obtained in generally a discontinuous patchwork. For a two-dimensional proximal femur model this patchwork shows a good resemblance with the density distribution of a real proximal femur. It is shown that the discontinuous end configuration is dictated by the nature of the differential equations describing the remodeling process. This process can be considered as a nonlinear dynamical system with many degrees of freedom, which behaves divergent relative to the objective, leading to many possible solutions. The precise solution is dependent on the parameters in the remodeling rule, the load and the initial conditions. The feedback mechanism in the process is self-enhancing, denser bone attracts more strain energy, whereby the bone becomes even more dense. It is suggested that this positive feedback of the attractor state (the strain energy field) creates order in the end configuration. In addition, the process ensures that the discontinuous end configuration is a structure with a relatively low mass, perhaps a minimal-mass structure, although this is no explicit objective in the optimization process. It is hypothesized that trabecular bone is a chaotically ordered structure which can be considered as a fractal with characteristics of optimal mechanical resistance and minimal mass, of which the actual morphology depends on the local (internal) loading characteristics, the sensor-cell density and the degree of mineralization

Intramedullary fixation with screwed, conical stems--unsolicited results from animal experiments (Article)

1992-07-08T00:00:00Z

For the purpose of studying bone remodeling around prostheses, a segmental replacement for the goat tibia was designed, using a conical, screw-threaded, hydroxyapatite-coated stem for fixation. Eight goats were provided with the implant, seven of which loosened within 10 days post-operatively, displaying progressive radiolucency and gross rotational motion. The eighth one also loosened radiographically, but developed a stabilizing callus bridge to prevent motion. A second design of similar shape and coating, but lacking the screw threads, was designed and also applied in eight animals. In this case, no loosening occurred in the first 6 weeks post-operatively. It is concluded that the application of screwed intramedullary stems for prosthetic fixation is not a viable concept, because the threads prevent the stem from subsiding and restabilizing when minor initial interface stress-relaxation and remodeling has occurred.

The relationship between stress shielding and bone resorption around total hip stems and the effects of flexible materials (Article)

1992-01-01T00:00:00Z

Bone resorption around hip stems is a disturbing phenomenon, although its clinical significance and its eventual effects on replacement longevity are as yet uncertain. The relationship between implant flexibility and the extent of bone loss, frequently established in clinical patient series and animal experiments, does suggest that the changes in bone morphology are an effect of stress shielding and a subsequent adaptive remodeling process. This relationship was investigated using strain-adaptive bone-remodeling theory in combination with finite element models to simulate the bone remodeling process. The effects of stem material flexibility, bone flexibility, and bone reactivity on the process and its eventual outcome were studied. Stem flexibility was also related to proximal implant/bone interface stresses. The results sustain the hypothesis that the resorptive processes are an effect of bone adaptation to stress shielding. The effects of stem flexibility are confirmed by the simulation analysis. It was also established that individual differences in bone reactivity and mechanical bone quality (density and stiffness) may account for the individual variations found in patients and animal experiments. Flexible stems reduce stress shielding and bone resorption. However, they increase proximal interface stresses. Hence, the cure against bone resorption they represent may develop into increased loosening rates because of interface debonding and micromotion. The methods presented in this paper can be used to establish optimal stem-design characteristics or check the adequacy of designs in preclinical testing procedures.

Trends of mechanical consequences and modeling of a fibrous membrane around femoral hip prostheses (Article)

1990-11-05T00:00:00Z

In the present study, the effects of a fibrous membrane between cement and bone in a femoral total hip replacement were investigated. The study involved the problem of modeling this fibrous membrane in finite-element analyses, and its global consequences for the load-transfer mechanism and its resulting stress patterns. A finite-element model was developed, suitable to describe nonlinear contact conditions in combination with nonlinear material properties of the fibrous membrane. The fibrous tissue layer was described as a highly compliant material with little resistance against tension and shear. The analysis showed that the load transfer mechanism from stem to bone changes drastically when such a membrane is present. These effects are predominantly caused by tensile loosening and slip at the interface, and are enhanced by the nonlinear membrane characteristics. Using parametric analysis, it was shown that these effects on the load-transfer mechanism cannot be described satisfactorily with linear elastic models. Most importantly, the fibrous tissue interposition causes excessive stress concentrations in bone and cement, and relatively high relative displacements between these materials.

Adaptive bone-remodeling theory applied to prosthetic-design analysis (Article)

1987-01-01T00:00:00Z

The subject of this article is the development and application of computer-simulation methods to predict stress-related adaptive bone remodeling, in accordance with 'Wolff's Law'. These models are based on the Finite Element Method (FEM) in combination with numerical formulations of adaptive bone-remodeling theories. In the adaptive remodeling models presented, the Strain Energy Density (SED) is used as a feed-back control variable to determine shape or bone density adaptations to alternative functional requirements, whereby homeostatic SED distribution is assumed as the remodeling objective. These models are applied to investigate the relation between 'stress shielding' and bone resorption in the femoral cortex around intramedullary prostheses, such as used in Total Hip Arthroplasty (THA). It is shown that the amount of bone resorption depends mainly on the rigidity and the bonding characteristics of the implant. Homeostatic SED can be obtained when the resorption process occurs at the periosteal surface, rather than inside the cortex, provided that the stem is adequately flexible.