SELECTIVE MOTOR HYPERREINNERVATION USING MOTOR ROOTLET TRANSFER - AN EXPERIMENTAL-STUDY IN RAT BRACHIAL-PLEXUS

Misdirection of sensory fibers into motor pathways is, in part, respon sible for the poor results obtained after peripheral nerve repair. Aft er avulsion of the C-5 root in rats, the authors connected a C-4 ventr al rootlet to the musculocutaneous nerve by means of a sural nerve gra ft. In this way, they were able to increase the number of regenerating motor fibers and avoid growth of sensory fibers into the nerve grafts . Functional recovery was evaluated electrophysiologically and histolo gically. The origin of the axons that reinnervated the nerve graft was analyzed by means of morphological studies including retrograde label ing procedures. Motor neurons survived and regenerated after the rootl et transfer and there was no functional impairment. Many neurons were retrograde labeled in the ventral horn and widespread biceps muscle re innervation was demonstrated with recovery of nearly normal electrophy siological properties. Motor hyperreinnervation of the musculocutaneou s nerve was observed. This high degree of reinnervation in a long (40- mm) graft was attributed to the good chance that a muscle fiber can be reinnervated by a motor fiber when the number of regenerating motor n eurons is increased and when competitive sensory fibers are excluded f rom reinnervation.