The effect of non-freezing local cooling on nerve injury in rabbits was studied by measuring the changes of latencies and amplitudes of the compound action potentials, as well as the histological and needle electromyographic changes.

The experimental rabbits were divided into three groups: Experimental Group 25, Sham 19, and Control 15. Non-freezing cooling, 1-5℃, was applied to the sciatic nerve after exposing at the proximal thigh. The Control and Sham Groups did not show any electrophysiologic or histologic changes after procedure. In the Experimental Group, after the proximal nerve damage, the nerve conduction study showed significant decrease in the amplitude with the stimulation of the proximal and distal regions, without any changes in the latencies. The needle electromyography of the gastrocnemius muscles began to show the positive sharp waves and the fibrillation potentials on the third day after the non-freezing cooling, while the histological changes began immediately after the cooling on the electron microscopic examination. The axonal degenerative changes at the level of cooling were most pronounced during the first 3-7 days after the cooling, and the regeneration process began to notice on 14-28 days after the cooling.

The fiber degeneration was significantly greater for unmyelinated fibers than myelinated fibers. The electrophysiologic and histologic results suggest that the nerve injury induced by the local non-freezing cooling is primarily due to the proximal axonal damage, i.e., axonotmesis process, with greater vulnerability of the unmyelinated fibers.