Some effects of prolonged constriction on nerve regeneration in the rabbit

Serial nerve conduction studies have been used to study the time-course of regeneration after tibial nerve crush in the rabbit, and the effect on this of a constricting ligature 5 mm distal to the site of crush. Transverse sections from the region of the ligature showed that when constriction was severe, the regenerating fibers had difficulty in penetrating the constricted region, and that some took an aberrant course in superficial connective tissue outside the ligature. In 2 out of 6 animals no fibres succeeded in passing through the centre of ligature, but aberrant fibres were able to re-enter distal fascicles and to reinnervate distal muscles. When compared with findings after crush alone, the time taken to reinnervate distal muscles was increased by a ligature, and distal fibre diameter and motor conduction velocity remained low. Low voltage, long-duration, polyphasic muscle action potentials were evoked by distal nerve stimulation, and axon reflexes suggested excessive axon branching within nerve trunks. Since these changes were seen in the distal parts of both constricted and aberrant fibres, they cannot be attributed to constriction alone. Similar changes might be expected in other peripheral nerve lesions in which loss of fascicular continuity and neuroma formation occur.