Tenotomy prevents the functional improvement of a muscle reinnervated with a chronically severed nerve

Functional recovery improvement is related to aberrant reinnervation trimming. A comparative study using fresh or predegenerated nerve grafts

Experimentally predegenerated nerve grafts have been demonstrated to improve recovery. In a 12 month-long study, we compared the degree of recovery of conventional and predegenerated grafts in rat median nerve repair. To induce predegeneration the ulnar donor nerve was crushed and grafting to the median nerve was performed 2 weeks later. The day of recovery and the improvement of finger flexion strength were studied by the grasping test. At 3, 6, 9, and 12 months after surgery retrograde labeling studies and flexor carpi radialis muscle ATPase histochemistry were performed. In the predegenerated grafts, the recovery of finger flexion occurred 19.6+/-1.5 days after surgery and was significantly faster than that in the conventional group. Twelve months after surgery, a similar rate of 85% of grasping strength recovery in relation to the normal control rats was demonstrated for the conventional and predegenerated grafts. After grafting, a larger number of motoneurons, compared to the normal controls, were retrograde labeled in the median nerve. This surplus of retrograde labeled motoneurons in the predominantly sensory branch of the median nerve represented misdirected motor fibers. There was a time-related decrease in the number of labeled motoneurons, which correlated to functional grasping strength recovery. Muscle reinnervation induced a predominance of type I over type II muscle fibers. Forty percent of type I fibers were grouped indicating that collateral sprouting plays a prominent role during muscle reinnervation. Regeneration in predegenerated grafts was faster but the final rate of recovery was similar to conventional grafts.