http://repub.eur.nl/res/aut/8921/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/37660/ 2012-09-17T00:00:00Z http://repub.eur.nl/res/pub/17380/ 2009-01-01T00:00:00Z Background: In a previous study, ligaments that connect the extraforaminal lumbar spinal nerves with the fibrous capsule of the facet joints and the dorsolateral side of the intervertebral disc were described. This anatomical configuration suggests a mechanical role in transferring extraforaminal spinal nerve traction. Methods: One embalmed human lumbar spine was dissected from the twelfth thoracic vertebra to the first sacral vertebra to isolate the twelfth thoracic to the fourth lumbar spinal nerves. The spinal nerves from L1 to L4 were pulled at different angles with respect to the axis of the spine. Forces of 1-6 N were applied. The displacements of reflective markers glued to the proximal and distal ends of the adjoining ligaments were recorded with a video system. Findings: The spinal nerve proximal of the extraforaminal ligaments stays centred in the intervertebral foramen when pulling at an angle. At levels L1-L4 strain reduction by the extraforaminal ligaments was largest when pulling at a wider angle to the spinal axis in the sagittal plane. Proximal to the extraforaminal ligaments less displacement was seen compared to the displacement distal of the extraforaminal ligaments when pulling in longitudinal direction. A graded decrease in the displacement proximal to the extraforaminal ligaments was seen from the levels L1-L4. Interpretation: Extraforaminal ligaments play an important role in the prevention of damage due to spinal nerve traction. The proximal attachments secure a spinal nerve position central in the intervertebral foramen and also reduce longitudinal tension. http://repub.eur.nl/res/pub/30255/ 2008-08-01T00:00:00Z The study consisted of biomechanical modelling and in vitro experiments. The objective of the study was to find a mechanical cause of acute low back pain (LBP) in everyday situations. The precise mechanism producing LBP is still under discussion. Most biomechanical studies link the concepts of stooped postures and buckling instability of the spine under high compressive load. No biomechanical model addresses situations with small or neglectable compressive spinal load. The proposed conceptual model describes strain on the iliolumbar ligaments (ILs) when slouching from standing upright. Delayed or absent recruitment of back muscles that protect against hyperkyphosis of the lumbar spine is a conditional factor. Erector spinae and multifidus muscle forces are included, representing a bifurcation in back muscle force: one part acting on the iliac bones and one part acting on the sacrum. The multifidus muscle action on the sacrum may produce nutation which can be counteracted by pelvic floor muscles, which would link back problems and pelvic floor problems. The effect of simulated muscle tension on the ILs and the L5-S1 intervertebral disc angle was measured using embalmed specimens. Forces were applied to simulate erector spinae and sacral part of multifidus tension, bilateral up to 100 N each. Strain gauge sensors registered elongation of the ILs. Explorative biomechanical model calculations show that dynamic slouching, driven by upper body weight and (as an example) rectus abdominis muscle force may produce failure load of the spinal column and the ILs. The quasi-static test on embalmed specimens showed a significant increase of IL elongation with simulated rectus abdominis muscle force. Adding erector spinae or multifidus muscle tension eased the ILs. Sudden slouching of the upright trunk may create failure risk for the spine and ILs. This loading mode may be prevented by controlling loss of lumbar lordosis with erector spinae and multifidus muscle force. http://repub.eur.nl/res/pub/28968/ 2008-03-01T00:00:00Z Effective stabilization of the sacroiliac joints (SIJ) is essential, since spinal loading is transferred via the SIJ to the coxal bones, and further to the legs. We performed a biomechanical analysis of SIJ stability in terms of reduced SIJ shear force in standing posture using a validated static 3-D simulation model. This model contained 100 muscle elements, 8 ligaments, and 8 joints in trunk, pelvis, and upper legs. Initially, the model was set up to minimize the maximum muscle stress. In this situation, the trunk load was mainly balanced between the coxal bones by vertical SIJ shear force. An imposed reduction of the vertical SIJ shear by 20% resulted in 70% increase of SIJ compression force due to activation of hip flexors and counteracting hip extensors. Another 20% reduction of the vertical SIJ shear force resulted in further increase of SIJ compression force by 400%, due to activation of the transversely oriented M. transversus abdominis and pelvic floor muscles. The M. transversus abdominis crosses the SIJ and clamps the sacrum between the coxal bones. Moreover, the pelvic floor muscles oppose lateral movement of the coxal bones, which stabilizes the position of the sacrum between the coxal bones (the pelvic arc). Our results suggest that training of the M. transversus abdominis and the pelvic floor muscles could help to relieve SI-joint related pelvic pain. http://repub.eur.nl/res/pub/29322/ 2008-02-01T00:00:00Z Objective: Several tests have been developed to determine the extent of sacroiliac asymmetry during pregnancy-related pelvic girdle pain (PGP). This blinded control study investigated the intertester reliability of 3 such tests used in PGP. Methods: A total of 62 women (ages 20-40 years) were recruited from regional obstetric practices and subsequently divided into 3 groups: (1) 20 women without PGP who were pregnant for more than 20 weeks, (2) 22 women with PGP who were pregnant for more than 20 weeks, and (3) a control group of 20 women who were not pregnant and had no back pain or PGP. All tests were performed by 2 physiotherapists independently of each other and blinded to each other's results. The 3 tests were the thumb-posterior superior iliac spines test, the heel-bank test, and the abduction test. Results: To determine the level of agreement between the 2 testers, κ values were calculated. The overall κ is 0.30 (range, -0.22 to 0.83), which is considered as a poor agreement. The percentage agreement per test/category ranged from 45% to 95%. Conclusion: This study of 3 tests used to determine asymmetry of the sacroiliac joints in women with pregnancy-related PGP showed them to have a poor intertester reliability. http://repub.eur.nl/res/pub/30235/ 2008-02-01T00:00:00Z Pregnancy-related low back and pelvic pain (PLBP) is a frequent complication of pregnancy. Although pathological mechanisms underlying PLBP are obscure, dysfunction of the sacroiliac joints (SI-joints) seems to play an important role. A cross-sectional study was performed on 24 pregnant women with and without PLBP. The objective was to determine muscle activation patterns of trunk and leg muscles during the active straight leg raising test (ASLR) and static hip flexion, and to determine maximal hip flexion force at 0 and 20 cm leg raise height. Moreover, the effort to raise the leg was scored. The measurements resulted in several significant differences between the patients and healthy controls; among others (a) patients scored subjectively more effort during ASLR, (b) at both 0 and 20 cm leg raise height patients had less hip flexion force, and (c) patients developed more muscle activity during ASLR. Since pregnant women with PLBP developed a higher muscle activity during ASLR with a significantly lower output at 0 and 20 cm than healthy pregnant women, it could be proposed that the ASLR demonstrates a disturbed load transfer across the SI-joints in this population. http://repub.eur.nl/res/pub/36396/ 2007-10-01T00:00:00Z Background: One of the main ergonomic problems during surgical procedures is the surgeon's awkward body posture, often accompanied by repetitive movements of the upper extremities, increased muscle activity, and prolonged static head and back postures. In addition, surgeons perform surgery so concentrated that they tend to neglect their posture. These observations suggest the advantage of supporting the surgeon's body during surgical procedures. This study aimed to design a body support and to test its potential. Methods: The optimum working condition for a surgeon is a compromise between the spine and arm positions and the level of effort and fatigue experienced performing a procedure. The design vision of the Medisign group has led to the development of an ergonomic body support for surgeons that is suitable for use during both open and minimally invasive procedures. The feasibility of the newly designed ergonomic body support was assessed during seven surgical procedures. Electromyography (EMG) was performed for back and leg muscles using the body support in an experimental setting. Results: Six of seven participating surgeons indicated that the body support was comfortable, safe, and simple to use. The EMG results show that supporting the body is effective in reducing muscle activity. The average reduction using chest support was 44% for the erector spinae muscle, 20% for the semitendinosus muscle, and 74% for the gastrocnemius muscle. The average muscle reduction using semistanding support was 5% for the erector spinae, 12% for the semitendinosus muscle, and for 50% for the gastrocnemius muscle. Conclusion: The results of this study imply that supporting the body is an effective way to reduce muscle activity, which over the long term may reduce physical problems and discomfort. Additionally, the product supports the surgeon in his natural posture during both open and minimally invasive procedures and can easily be adapted to the current layout of the operating theater. http://repub.eur.nl/res/pub/10472/ 2006-11-03T00:00:00Z Afscheidscollege Prof.dr.ir. Chris J. Snijders, Hoogleraar Medische Technologie Erasmus Universiteit Rotterdam en Afdelingshoofd Biomedische Natuurkunde en Technologie, Erasmus MC. Uitgesproken 3 november 2006 http://repub.eur.nl/res/pub/15686/ 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. http://repub.eur.nl/res/pub/31808/ 2005-05-01T00:00:00Z Background: To investigate the stiffness and strength of completely unstable pelvic fractures fixated both anteriorly and posteriorly under cyclic loading conditions, the authors conducted a randomized, comparative, cadaveric study. Methods: In 12 specimens, a Tile C1 pelvic fracture was created. The authors compared the intact situation to anterior plate fixation combined with one or two sacroiliac screws. In 2,000 measurements, each pelvis was loaded with a maximum of 400 N. The translation and rotation stiffness of the fixations were measured using a three-dimensional video system. Furthermore, the load to failure and the number of cycles before failure were determined. Results: Both translation and rotation stiffness of the intact pelvis were superior to the fixated pelvis. No difference in stiffness was found between the techniques with one or two sacroiliac screws. However, a significantly higher load to failure and significantly more loading cycles before failure could be achieved using two sacroiliac screws compared with one screw. Conclusion: Although the combination of anterior plate fixation combined with two sacroiliac screws is not as stable as the intact pelvis, in this study, embalmed aged pelves could be loaded repeatedly with physiologic forces. Given the fact that the average trauma patient is younger and given the fact that the quality (or grip) of the fixation was a significant covariable for longer endurance of the fixation, this suggests that direct postoperative weight bearing could be possible if these results are confirmed in further research. Copyright http://repub.eur.nl/res/pub/31829/ 2003-04-15T00:00:00Z The objective of this study was to determine the influence of scapular support on the effects of lumbar support and to prove that a high and straight backrest is inappropriate. In literature the importance of a lumbar support is noted, although data about optimal dimensions is an under-researched topic and in earlier studies on force distribution and muscle activity the backrest had a fixed form. The lumbar support is needed to maintain the lumbar lordosis but no studies deal with the question of the precise dimensions of the backrest at shoulder level. With a specially designed apparatus, forces on shoulder and seat were measured separately, and the force on the pelvis calculated, while varying seat and backrest inclination within the range from 0° to 17°. Seat-to-backrest angle (at the level of lumbar support) was kept constant at 90°. The distance between the tangent to the lumbar support and the parallel tangent to the scapular support was varied from 0, 2, 4, 6 and 8 cm. This distance is called the free shoulder space. Electromyography was measured at the erector spinae at the levels of the L1, T8 and T5 vertebrae. For all seat angles, a free shoulder space of d = 0 cm resulted in the highest back muscle activity. In agreement with the biomechanical model, EMG activity reduced with an increase of seat tilt and increase of free shoulder space. With increasing free shoulder space, a larger part of the total backrest force was carried by the lumbar support. This study shows that a high and straight backrest overrules lumbar support. Offering free shoulder space of at least 6 cm reduces back muscle activity and allows for lumbar support. http://repub.eur.nl/res/pub/9784/ 2001-01-01T00:00:00Z The iliolumbar ligament has been described as the most important ligament for restraining movement at the lumbosacral junction. In addition, it may play an important role in restraining movement in the sacroiliac joints. To help understand its presumed restraining effect, the anatomy of the ligament and its orientation with respect to the sacroiliac joints were studied in 17 cadavers. Specific dissection showed the existence of several distinct parts of the iliolumbar ligament, among which is a sacroiliac part. This sacroiliac part originates on the sacrum and blends with the interosseous sacroiliac ligaments. Together with the ventral part of the iliolumbar ligament it inserts on the medial part of the iliac crest, separate from the interosseous sacroiliac ligaments. Its existence is verified by magnetic resonance imaging and by cryosectioning of the pelvis in the coronal and transverse plane. Fibre direction, length, width, thickness and orientation of the sacroiliac part of the iliolumbar ligament are described. It is mainly oriented in the coronal plane, perpendicular to the sacroiliac joint. The existence of this sacroiliac part of the iliolumbar ligament supports the assumption that the iliolumbar ligament has a direct restraining effect on movement in the sacroiliac joints. http://repub.eur.nl/res/pub/31883/ 1995-02-01T00:00:00Z Both with respect to the aspect of pressure sores and of comfort, the inclination of backrest and seat are, amongst other factors, important design criteria. In this study the combination of seat and backrest inclination which reduces shear forces on the seat in passive seating forms the centre of attention. A biomechanical model was developed to predict these combinations and a new measurement apparatus was used for verification of the model on 10 healthy subjects (age 24.4 S.D. 2.1 yr, height 1.77 S.D. 0.08 m, mass 66.3 S.D. 11 Kg). For chairs it was found that when little shear is accepted, a fixed inclination between seat and backrest can be chosen between 90° and 95°. For beds a parabolic relationship was found between seat and backrest inclination with a maximum seat inclination of 20° at a backrest inclination of 50°. When lying with the knees bent to a position with equal inclination of thighs and shanks, the model predicts a shear force on the seat that shoves the person into the bed for every combination of seat and backrest inclination.Both with respect to the aspect of pressure sores and of comfort, the inclination of backrest and seat are, amongst other factors, important design criteria. In this study the combination of seat and backrest inclination which reduces shear forces on the seat in passive seating forms the centre of attention. A biomechanical model was developed to predict these combinations and a new measurement apparatus was used for verification of the model on 10 healthy subjects (age 24.4 S.D 2.1 yr, height 1.77 S.D. 0.08 m, mass 66.3 S.D. 11 Kg). For chairs it was found that when little shear is accepted, a fixed inclination between seat and backrest can be chosen between 90° and 95°. For beds a parabolic relationship was found between seat and backrest inclination with a maximum seat inclination of 20° at a backrest inclination of 50°. When lying with the knees bent to a position with equal inclination of thighs and shanks, the model predicts a shear force on the seat that shoves the person into the bed for every combination of seat and backrest inclination. http://repub.eur.nl/res/pub/8552/ 1995-01-01T00:00:00Z To investigate the origin of fractures at the distal locking site of the Gamma nail, we loaded ten paired human cadaver femora fixed with a Gamma nail in torsion until they fractured. When an awl was hammered in to start the hole for distal locking a fissure appeared in the lateral cortex of all the femora, and the mean torsional load to create a fracture was reduced by 57.8% compared with that in a control group in which the distal locking hole had been started with a centre drill. When an additional drill hole was made, the mean failure load in torsion decreased by 35.7%. We strongly recommend that an awl should not be used at the distal locking site of the Gamma nail; we recommend the use of a centre drill. Additional drill holes should be avoided because they act as stress raisers. http://repub.eur.nl/res/pub/26806/ 1984-11-14T00:00:00Z Rede, uitgesproken bij de aanvaarding van het ambt van Gewoon Hoogleraar in de Medische Technologie aan de Faculteit der Geneeskunde van de Erasmus Universiteit Rotterdam, op 14 november 1984