Article
Structural functional relationship in peripheral nerve regeneration: Functionality of axon regeneration after sciatic nerve injury
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Published: | May 20, 2011 |
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Introduction: Repair of peripheral nerve gaps still represents a clinical challenge. Despite decades of research, autologous nerve grafting is still regarded as the preferred bridging material. A variety of functional tests is available to assess the functionality of axon regeneration. At present, there is not a clear preference of behavioral tests to assess the functionality of axon regeneration. We, therefore, made an attempt to find differences in the suitability of behavioral tests to assess functionality of axon regeneration after sciatic nerve injury.
Materials and methods: We compared the neurotmesis lesion (autologous nerve grafting of a 2 cm defect) with an axonotmesis lesion (standardized crush model) in the rat sciatic nerve model. In each case, the modality “Function” was examined with two independent and well established behavioural tests, i.e. the Static Sciatic Index (SSI) for static parameters and the CatWalk gait analysis system for dynamic parameters. For the modality “Structure” we used conventional histomorphometry (semithin, toluidin blue staining; number of fibers, G-ratio) and transmissionelectron microscopy as well as retrograde tracing studies with examination of both sensible (DRG) and motor neurons (spinal cord).
Results: In contrast, the modality “Function” displayed a more differentiated pattern by comparing SSI (static) and CatWalk (static and dynamic) parameters. In axonotmesis, both CatWalk and SSI showed a significant recovery. However, regarding neurotmesis, a significant recovery could be displayed by SSI, but not by the CatWalk system (e.g. print area, intensity, stance swing phase and coupling parameters). For the modality “Structure” we found significant differences between axonotmesis and neurotmesis lesions regarding conventional histomorphometry (axon count, axon diameter, G-ratio) and retrograde tracing experiments.
Conclusion: We could prove that neither the functional tests nor structural tests alone give an impression of global regeneration. Instead, only a set of multimodal analysis techniques can give an impression on the degree and efficacy of regeneration.