Limited longitudinal sliding of the median nerve in patients with carpal tunnel syndrome.

During normal movements or changes in position of the limbs, nerve structures must accommodate the resulting changes in length of the nerve path. In patients with carpal tunnel syndrome, we monitored electrophysiologically the longitudinal adjustment of the median nerve to positions of extreme flexion and extreme extension of the wrist and elbow, by measuring the differences induced in the latency of the sensory nerve action potential (SNAP) recorded in the forearm and upper arm. In patients, the latency difference was significantly shorter than in normal subjects (0.196 +/- 0.084 ms vs. 0.088 +/- 0.059 ms in the forearm, and 0.485 +/- 0.122 ms vs. 0.129 +/- 0.086 ms in the upper arm). These results indicate that the displacement of the source of the median nerve SNAP with movements of flexion and extension is limited in patients with carpal tunnel syndrome. Such an abnormality may partly underlie the pathophysiology of entrapment syndromes.