Background
Functional outcomes after vascularized composite allotransplantation (VCA) depend on nerve regeneration. After transplantation, the recipient peripheral nerve axons slowly grow and reinnervate the graft. Meanwhile, the target composite tissues (i.e., muscle, nerves) are chronically denervated, causing significant damage to axons, Schwann cells, and muscle, which leads to decreased nerve regeneration potential. There are currently no studies that reliably measure the effects of chronic denervation (CD) on graft function. Thus, we have developed a novel nerve injury rat model that optimizes the measurement of functional recovery after CD.
Methods
In our forelimb chronic denervation model, the median nerve was transected at the mid-humerus level and left in discontinuity for 0, 8, or 12 weeks. After the period of CD, the distal median nerve stump was co-apted to the proximal end of a freshly axotomized ulnar nerve. Group 1 rats underwent 8 weeks of CD (n = 8); Group 2 underwent 12 weeks of CD (n = 8); Group 3 (positive control) did not undergo CD but instead underwent immediate ulnar-median neurorrhaphy (n = 8); and Group 4 (naive control) did not undergo any surgery (n = 8). Functional recovery was monitored weekly by measuring grip strength, feeding ability, and compound muscle action potentials (CMAPs) in median nerve-innervated muscles. Animals were sacrificed at 14 weeks after ulnar-median neurorrhaphy for assessment of axonal regeneration and degree of muscle atrophy.
Results
Fourteen weeks after ulnar-median neurorrhaphy, Group 3 rats demonstrated significantly greater functional recovery, as compared with Group 1. Group 3 animals demonstrated greater grip strength than Group 1 (2.2 ± 0.3 Newtons vs. 1.0 ± 0.1 Newtons, P=0.001), improved feeding (score of 7.3 ± 0.05 vs. 6.0 ± 0.04, P<0.0001), and greater CMAPs (1.7 ± 0.07 millivolts vs. 0.5 ± 0.04 millivolts, P = 0.0001). Furthermore, forelimb flexor muscle weights were significantly different between Group 3 and 1 (0.82 g vs. 0.53 g; P < 0.00001). Results for Group 2 and 4 animals are pending.
Conclusion
This novel forelimb chronic denervation model provides the first translatable animal model to assess functional recovery after chronic denervation of peripheral nerves and can be used to reliably assess future therapeutics aimed at augmenting extremity function following VCA.
Figure 1.
