Impairment of motor recovery after late nerve suture: experimental study in the rabbit. Part 2: morphological findings.

To study motor recovery after increasingly late nerve suture, we severed 75 rabbit peroneal nerves and reanastomosed them by microsurgical epineural technique after a delay of up to 12 months. Functional, electromyographic, and morphological parameters were used to evaluate the quality of motor function 6 months after suture. This second part of the study deals with the results of the morphological examinations (nerve, motor end-plate, and muscle). In examining the histological picture of the peroneal nerve, individual variations in its neurotization distal to the suture were more obvious than were variations with increasing presuture denervation periods. Histological and histochemical changes within the muscle increased significantly with later nerve suture. Important alterations at the motor end-plate were observed in the very late suture group. From the findings of both parts of the present study, the following conclusions can be drawn. The normal anatomical (histochemical) picture of the muscle is not restored after a nerve suture, not even after primary suture. The important degenerative muscular changes after very late nerve suture are not due to alterations within the nerve alone; structural changes in the motor end-plates and muscle fibers are equally important. These findings seem to be relevant when discussing the indication for nerve suture in patients with a long-standing nerve injury.