http://repub.eur.nl/res/aut/431/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/37661/ 2012-09-17T00:00:00Z http://repub.eur.nl/res/pub/26696/ 2011-07-01T00:00:00Z The purpose of this study was to compare the biomechanical properties of a novel wrap around tendon repair method with those of the standard Pulvertaft technique used for tendon reconstructions. Seventy-two porcine extensor tendons were used to create 36 reconstructions in six sets of six repairs, each using one of the two surgical techniques with differing lengths of the reconstructions. All the reconstructions were tested in vitro by cyclic tensile loading, resulting in the time-zero strength. When only the size of the repair and the strength were compared, and length of the reconstruction was not taken in consideration, the 'wrap around' reconstructions were of similar strength but less bulky than the Pulvertaft repairs. In conclusion, the 'wrap around' technique gives a thinner reconstruction which is as strong as, or stronger than the Pulvertaft technique, depending on the amount of weaves. http://repub.eur.nl/res/pub/33718/ 2011-01-15T00:00:00Z The use of ultrasound-guided electrode positioning in near-nerve myography was investigated. This is a minimally invasive technique that allows repeated measurements to increase accuracy and hence decreases animal numbers. Ultrasound imaging of the sciatic nerve was performed in nine rats using a 55. MHz high-end transducer. Once visualised, a monopolar needle electrode was placed through the skin near this nerve. Upon stimulation, two surface electrodes, placed over the gastrocnemius muscle, recorded compound muscle action potentials (CMAPs). Reproducibility was tested having two teams of investigators perform the recordings consecutively. Reliability of the procedure was determined by comparing the ultrasound method to the conventional technique, which requires an incision through muscle and skin to expose the sciatic nerve. In all animals the sciatic nerve was visible on ultrasound images. Both methods showed CMAP latencies (duration was determined as the time interval between the onset latency and positive peak). The conventional method had a mean latency of 3.4 ± 0.5. ms, our method had a mean latency of 3.3 ± 0.5. ms. Reproducibility was excellent (observed latencies and amplitudes: 3.3 versus 3.3. ms and 25.6 ± 5.1. mV versus 22.5 ± 8.8. mV) resulting in a coefficient of variation for duration of 2.1% and for amplitude 6.7%. Interclass correlation coefficient was 0.828 for duration. Comparing the three different measurements no significant differences were found and our new method can therefore be considered reliable and comparable to the conventional method.Ultrasound-guided near-nerve needle positioning is a reproducible and reliable minimally invasive method for selectively eliciting CMAPs, which allows repeated CMAP measurements for studying nerve regeneration in rats. http://repub.eur.nl/res/pub/21293/ 2010-10-01T00:00:00Z Cold induced vasoconstriction (CIVC) is a way for mammals to reduce heat loss in an effort to maintain body core temperature. As blood flow to a cooled extremity is reduced, the amount of body heat lost at the cooled location is minimised. However, when the extremity temperature gets below a certain threshold, Cold induced vasodilatation (CIVD) occurs, a phenomenon that is believed to reduce the risk of local cold injuries.Many theories explaining the mechanism of the CIVD reaction have been postulated, but no consensus has been found. One of these theories is that the CIVD reaction is controlled neurally. To study the effect of neural influence on the vascularisation and rewarming patterns a new experimental set-up was designed. This set-up is able to measure responses in both hind paws simultaneously, creating the opportunity to study the effect of nerve injury on one limb and use the contralateral limb as a control.Ten rats received a sciatic nerve transection and repair of either the left (n=5) or the right (n=5) hind limb. Measurements were performed, 1 day pre-operatively, directly post-operatively, and at days 1, 7, 14, 21, 35 and 49 post-operatively.Although results are not significant, there is a tendency for the CIVD reaction to be reduced in the nerve injured paw until the nerve is regenerated around day 35.Further investigation of neural influence on the CIVD reaction will be necessary; this set-up may prove to be useful in future experiments to elucidate the mechanism of the CIVD reaction. http://repub.eur.nl/res/pub/32852/ 2010-08-17T00:00:00Z http://repub.eur.nl/res/pub/24105/ 2009-12-01T00:00:00Z Ultrasound-guided near-nerve neurography is a new tool that can be used to assess nerve regeneration before reinnervation occurs. In this study, ultrasound-guided near-nerve measurements were validated against axon diameter counts in rabbits during a 15-week regeneration period after a crush lesion of their peroneal nerve. The course of the nerve was determined ultrasonically, and the active near-nerve needle electrode was maneuvered just next to the nerve under ultrasound guidance. Measured action potentials were compared with axon diameter counts from histological sections of these same nerves. A moderate to good positive correlation was found, which reached a maximum of 0.7 at a cut-off of 3 μm, corresponding to the minimal size of the myelinated axons. Our results suggest that, following a similar validation study in humans, ultrasound-guided near-nerve neurography may be clinically useful when early evaluation of nerve activity is needed. http://repub.eur.nl/res/pub/25315/ 2009-08-27T00:00:00Z Repairs have been performed on porcine flexor tendons and subjected to tensile stress measurements to determine the effects and mechanism of core suture purchase (the length of the suture bite). Eighty-four pig trotter flexor profundus tendons were divided and repaired using four lengths of core suture purchase (1.33, 1, 0.66 and 0.33 cm) using a double modified Kessler repair (four strands, two knots) with a peripheral epitendinous suture. Tendon purchase was achieved by either bilateral equal purchase lengths or with one tendon purchase at a fixed depth of 1 cm. A separate group of tendons were incubated in blood for 24 hours to simulate the wound environment prior to testing. Tensile tests demonstrated a progressive increase of repair strength with purchase length. With the exception of the 0.33 cm group, video analysis demonstrated the mode of failure as suture failure and not due to suture pullout. Therefore, the increase in breaking strength cannot be attributed to a better grip of the tendon ends, but to the mechanical characteristics of the suture polymer. The tendency for the incubated tendons to fail more consistently by pullout rather than suture failure, particularly in the shorter purchase lengths, emphasises the importance of studying tendon purchase in vivo. The significance of ex vivo mechanical testing should be considered with caution. http://repub.eur.nl/res/pub/16371/ 2009-05-06T00:00:00Z The effects of core suture geometry on the mechanics of failure in flexor tendon surgery are investigated. Forty porcine flexor tendons were repaired using a Kessler; a Kessler-Pennington; a double Kessler; a continuous Kessler; and a cruciate repair. At maximum breaking strength, the cruciate repair gapped more then the double Kessler (12.8 mm vs 9.1 mm), but the double Kessler was less strong (37N vs 45 N). Transverse narrowing was 22% and 24% for the Kessler and the Kessler-Pennington, 11% for the double Kessler, and 0% for the continuous Kessler and the cruciate repair. Kessler-type sutures failed by suture breakage and the cruciate repair by pull-out. Under load, the transverse part of the Kessler sutures narrows, allowing longitudinal parts to lengthen, leading to gapping. The double Kessler shortened transverse segment decreases gapping. Eliminating a transverse component (the cruciate repair) decreased gapping, but the cruciate failed at higher loads by suture pull-out. http://repub.eur.nl/res/pub/15134/ 2008-09-30T00:00:00Z For early assessment of axonal outgrowth after trauma, the nerve is surgically exposed to enable compound nerve action potential (CNAP) recordings across the lesion site. Near-nerve neurography, with needle electrodes placed transcutaneously near the nerve, could be a minimally invasive alternative if the needle placement procedure and low reproducibility are improved. We developed ultrasound-guided near-nerve neurography, which facilitates needle placement, and assessed its potential for evaluating nerve regeneration. Measurements were performed at varying times after crush lesion of the peroneal nerve of 25 rabbits. To test if ultrasound-guided near-nerve signals could be measured prior to muscle reinnervation, they were compared with recordings of compound muscle action potentials. A comparison with conventional intra-operative CNAP recordings was made by measuring nerve signal amplitude with both techniques and by assessing reproducibility. In all cases where intra-operative signals could be measured, near-nerve signals were also detected. Compound nerve activity could be recorded after 5 weeks, whereas compound muscle activity appeared after approximately 8 weeks. Reproducibility was slightly better for near-nerve than for intra-operative recordings. We conclude that ultrasound-guided near-nerve neurography is able to assess nerve regeneration well before compound muscle activity can be detected. Its accuracy and reproducibility are similar to those of conventional intra-operative recordings. http://repub.eur.nl/res/pub/30675/ 2004-11-24T00:00:00Z The peripheral nervous system is designed to connect the orchestrations of brain and spinal cord to the rest of the body. In addition, it connects the outside world and that same brain, gathering information from numerous sensory organs in our skin and from our other “senses”. Injury to a nerve subsequently results in impairment of function as well as impairment of that information gathering system. In order to restore the damage, a series of complex changes is triggered in the cell body and the axon, all aimed at restoring motor and sensory function. However, different parts of the peripheral nervous system have different responses to injury. It is possible to distinguish three different parts: The cell body, the proximal segment and the distal segment. Proximal to the lesion, in the cell body and the proximal segment, the aim is to reconnect the axon to its effector organ as soon as possible. Distal to the lesion everything is aimed at creating an environment that allows reconnection of axons to happen. In order to accomplish this, the nerve proceeds through a number of morphological and electrophysiological changes. Although maybe not directly obvious, those morphological transformations after injury are reflected in electrophysiological changes. Previous research demonstrated changes in peak-peak amplitude of compound nerve action signals in the proximal segment after nerve transection and reconstruction45−48. However, the mechanisms involved however, are still unclear. The aim of this thesis is to explore the changes in the proximal segment and to clarify possible modifications to the proximal segment influencing repair. http://repub.eur.nl/res/pub/2659/ 2004-08-15T00:00:00Z Mice homozygous for the autosomal recessive mutation claw paw (clp) are characterized by limb posture abnormalities and congenital hypomyelination, with delayed onset of myelination of the peripheral nervous system but not the central nervous system. Although this combination of limb and peripheral nerve abnormalities in clp/clp mice might suggest a common neurogenic origin of the syndrome, it is not clear whether the clp gene acts primarily in the neurone, the Schwann cell or both. In the work described here, we address this question of cell autonomy of the clp mutation through reciprocal nerve grafting experiments between wild-type and clp/clp animals. Our results demonstrate that the clp mutation affects the Schwann cell compartment and possibly also the neuronal compartment. These data suggest that the clp gene product is expressed in Schwann cells as well as neurones and is likely to be involved in direct axon--Schwann cell interactions. Within the Schwann cell, clp affects a myelin-related signaling pathway that regulates periaxin and Krox-20 expression, but not Oct-6. http://repub.eur.nl/res/pub/12878/ 2000-01-01T00:00:00Z The POU domain transcription factor Oct-6 is a major regulator of Schwann cell differentiation and myelination. During nerve development and regeneration, expression of Oct-6 is under the control of axonal signals. Identification of the cis-acting elements necessary for Oct-6 gene regulation is an important step in deciphering the complex signalling between Schwann cells and axons governing myelination. Here we show that a fragment distal to the Oct-6 gene, containing two DNase I-hypersensitive sites, acts as the Oct-6 Schwann cell-specific enhancer (SCE). The SCE is sufficient to drive spatially and temporally correct expression, during both normal peripheral nerve development and regeneration. We further demonstrate that a tagged version of Oct-6, driven by the SCE, rescues the peripheral nerve phenotype of Oct-6-deficient mice. Thus, our isolation and characterization of the Oct-6 SCE provides the first description of a cis-acting genetic element that responds to converging signalling pathways to drive myelination in the peripheral nervous system.