[Experimental study on the vulnerability of the peripheral nerve].

UNLABELLED

Compression neuropathy can occur simultaneously at dual points on a nerve, but the details of such lesions are still unknown. An experimental study was performed in order to investigate the vulnerability of the peripheral nerve in the "double crush" situation. Materials and Methods The sciatic nerves of 46 adult dogs were used. Compression was applied by special devices, and the compression force was 15 g (27.6 mmHg). The animals were divided into three groups. Group 1: One device was applied to the sciatic nerve 3 cm distal to the sciatic tuberculum. Group 2: Two devices were applied simultaneously with a 2 cm interval. Group 3: Two devices were applied at the same sites as in Group 2, but the second was applied three weeks after the first. These three groups were followed electrophysiologically up to eight or ten weeks postoperatively, at which time histological studies were undertaken. Results Electrophysiological studies: In Group I, complete conduction block was never induced. Mean motor nerve conduction velocity (M.N.C.V.) was 39% of the preoperative value at three weeks and increased slightly at six weeks. In Group 2, complete conduction block was induced in 50% at six weeks. Mean M.N.C.V. was 34% of the preoperative value at three weeks, and there was no significant change after this time. In Group 3, complete conduction block was induced in 50% at five weeks after the second operation. Mean M.N.C.V. was reduced to 14% of the preoperative value at three weeks after the second operation.

HISTOLOGY

In Group 1, the number of large myelinated fibers was reduced at the site of compression and in the distal segment. Mean values for the diameter of the fibers distal to the compression site were shifted to the left when compared with the controls. In Groups 2 and 3, severer changes were noticed, especially in the segment distal to the site of the second compression. Conclusion Subclinical neuropathy was induced by a compression force of 15 g, and it was considered to be axonostenosis . The nerve had been compressed in the proximal region, became vulnerable to an additional compression trauma in the distal region. Even complete conduction block could be induced under such circumstances, and it was considered to be as axonocachexia . Impairment of axonal flow should be considered as a causes of the vulnerability.(ABSTRACT TRUNCATED AT 400 WORDS)