Tiam Mana Saffari

36 CHAPTER 2 revascularization in a conventional autograft is longitudinal inosculation (host vessels grow into the graft from both ends and anastomose with donor vessels) 21-23 . The evidence of peripheral neovascularization or dependence on the graft bed as a source of revascularization had not evolved until later when centripetal revascularization, growth from the surrounding tissue bed, was described 24 . Inosculation results in endothelial-lined formed vessels at the nerve graft coaptation site. When the nerve graft metabolic requirements exceed the ability of the inosculated vessels to provide adequate blood flow, centripetal revascularization occurs from the surrounding bed 25 . Previously, it was believed that inosculation occurs equally from both nerve graft ends, but recent research using novel micro CT visualization techniques has shown that inosculation occurs primarily from proximal to distal 26,27 . This supports the fact that success of the grafted nerve is partly affected by the length of the graft, as a longer graft is subject to higher risk of necrosis in the mid-section 25,27 . Prolonged denervation time leads to intraneural fibrosis and core necrosis negatively affecting the nerve regeneration process 20 . Moreover, it was realized that multiple thin diameter cable grafts instead of single large diameter grafts could overcome central necrosis secondary to faster revascularization in smaller diameter cables 28 . To appreciate the potential benefits and limitations of our understanding of vascularization, it is important to comprehend the basic physiology of its effect on nerve regeneration in basic science and clinical applications as discussed below. EFFECT OF VASCULARIZATION ON NERVE REGENERATION Basic science applications Since 1976, studies have suggested the superiority of VNGs. The major reason for the lack of evidence in peripheral nerve injuries is the fact that studies include the use of different animal species, reconstructive strategies, follow-up times and outcome measures to assess nerve regeneration. These methodological differences make translation from animal models to humans challenging and nearly impossible. An overview of the available studies is provided. It is postulated that vascularity improves results of nerve grafts by increasing the number of Schwann cells, while minimizing intraneural fibrosis and enhancing axonal