Muscle fiber type reorganization and behavioral functional recovery of rat median nerve repair with vascularized or conventional nerve grafts

In 1921, Ney introduced the concept of nerve grafts with preservation of the vascular blood supply. Today, over 70 years later, the use of vascularized nerve grafts in clinical practice is still controversial. Although the results of experiments with vascularized and conventional nerve grafts have been compared on the basis of electrophysiological and histological observations, the literature includes no vaJid comparison of the clinical and behavioral significance of these results. Therefore, in the experiments reported here, the rat median nerve was repaired using either a vascularized or a conventional ulnar nerve graft. The rates behavior between 0 and 360 days after surgery was assessed by the grasping test. Nienty-five, 120, 150, 210 and 360 days after surgery rats were submitted to retrograde labeling studies and muscle samples were removed and studied using routine hematoxilin-eosin and ATPase histochemistry. The present study provides evidence that autografting is a reliable procedure for nerve repair. Motor axons were able to reinnervate and largely respecify muscle properties. Reinnervation was not selective either at the nerve trunk level or at the muscle fiber. A mechanism of collateral pruning might have been present in the early phases of reinnervation. This mechanism was, however, self limiting and unable to correct all wrong projections. A mechanism of terminal sprouting was in part responsible for time-related improvement in muscle force recovery. While the present study does provide evidence that recovery was 20% faster in rats with vascularized grafts than in those with conventional grafts (P < 0.0001), it does not, however, provide evidence for better functional recovery in long-term assessment.