The influence of timing on the functional and morphological result after nerve grafting: an experimental study in rabbits.

Abstract

Clinical experience and experimental work in sheep have shown that a two-stage approach to restoring muscle function with a long nerve graft and free muscle grafting seems to be more beneficial than a one-stage approach. Based on a standardised experimental protocol, one-stage and two-stage nerve grafting approaches in rabbits were compared, and the actual differences in muscle force, together with morphological data, were calculated. In 20 rabbits the saphenous nerve was used as a 7 cm nerve graft. Animals were separated into two groups. In group 1, 10 rabbits underwent a one-stage approach to reinnervate the rectus femoris muscle. In the left hindlimb, the proximal end of the graft was coapted to the cut motor nerve branch of the vastus medialis muscle, and the distal end was coapted to the nerve branch of the rectus femoris muscle. In group 2, 10 rabbits underwent a two-stage approach, leaving the distal end of the nerve graft unconnected to the rectus femoris muscle in the first stage. In the second stage, this end was coapted to the freshly cut motor nerve branch of the rectus femoris muscle. After 15 months, the maximum tetanic tensions in the reinnervated rectus femoris muscle and the contralateral unoperated muscle were determined. The graft and the motor branch distal to the graft were biopsied in order to count the number of regenerated myelinated nerve fibres. The mean+/-s.d. maximum tetanic tensions in the reinnervated rectus femoris muscles were 10.6+/-4.9 N in group 1 and 21.4+/-1.1 N in group 2. Compared with the unoperated side, the muscle force following denervation and reinnervation was 38.3% in group 1 and 58.9% in group 2 (P=0.01). The mean+/-s.d. numbers of regenerated myelinated nerve fibres distal to the graft in the rectus femoris muscle branch were 737+/-340 in group 1 and 1487+/-1004 in group 2 (P=0.05). These results show that the neurotrophic effect of an immediately connected target organ is far outweighed by the adverse effect of the longer period of muscle denervation. Therefore, nerve grafting and muscle transplantation should not be performed in the same operation.