The influence of harvesting method on morphological changes in sural nerve graft and on the quality of motor and sensory recovery

Abstract

Dear Sir With interest I have read the article of Dr. Ivo Dzepina. This study claims that the use of ‘non-traumatized’ sural nerve grafts provide a better outcome than those harvested with the more traumatizing harvesting method of multiple transverse sections. The rationale is that ‘extensive ultrastructural damage with multi-focal fragmentation of myelin sheath...’ that did not occur in the proposed harvesting technique, which inflicts a longitudinal scar from knee to ankle, present such dramatic insult to regenerating axons, that the outcome is significantly poorer. Much could be said about the patient population, and evaluation techniques used, however, I want to simply ask the author what he thinks will happen to the harvested nerve after grafting. Yes, the nerve will degenerate, Schwann cells will undergo dramatic morphological changes, and the so precious myelin sheath will disintegrate! What is left is a disaster of cell debris, macrophages cleaning the mess and reactive Schwann cells providing a humoral environment conducive to axonal regeneration. With whatever method the nerve is harvested, after a few days they will all look alike. Regenerating axons require an environment that provides polymeric networks of several types of different macromolecules that not only serve as physical cues for directive axonal growth, but are also needed for nonneural cell populations for differentiation and physical integration. In recent years the importance of different surface molecules to aid in nerve regeneration have been more appreciated. It has been understood that protruding growth cones of the regenerating axons need a permissive substratum to successfully regenerate across longer distances. In conventional nerve grafts extracellular matrix molecules such as laminin-1, fibronectin, as well as more specialized cell surface molecules from either the integrin or the cadherin family are ubiquitous. Furthermore, this matrix is evidently necessary for appropriate differentiation and induction of specific gene expression of a number of non-neural cells such as Schwann cells, fibroblasts or migrating macrophages. These in turn will provide the necessary humeral environment for regenerating nerve fibres to survive the transient target-less state. The conventional nerve graft so far is the only biological resource we have that provides this environment, and it is too simplistic a thought to believe that the method of harvest will make a difference and I strongly disagree with the author’s conclusion. Lastly, figure 1 and figure 2 are micrographs of the same specimen of supposedly two different nerves, harvested with different techniques!