Effect of Carpal Tunnel Syndrome on the Ulnar Nerve at the Wrist: Sonographic and Electrophysiologic Studies.

Objectives-The aim of this study was to compare the ulnar nerve at the wrist by sonographic and electrophysiologic studies between patients with carpal tunnel syndrome and control participants and to verify the effect of carpal tunnel syndrome of the ulnar nerve at the wrist. Methods-Forty-two hands of patients with carpal tunnel syndrome and 37 hands of control participants were examined. Electrophysiologic studies of the ulnar nerve were done in all participants. The cross-sectional areas of the median and ulnar nerves at the wrist were evaluated by sonography. Fifteen hands of patients with carpal tunnel syndrome who underwent carpal tunnel release were also evaluated by sonography after the operation. Results-The ulnar nerve cross-sectional area of the patients with carpal tunnel syndrome (mean +/- SD, 5.16 +/- 1.04 mm(2)) was significantly larger than that of the controls (3.56 +/- 0.52 mm(2); P < .0001). After release of the transverse carpal ligament, the cross-sectional area of the ulnar nerve was significantly smaller than the size measured prior to surgery (P < .0001). The cross-sectional area of the median nerve was significantly correlated with that of the ulnar nerve (P < .05). However, no statistically significant difference was found between the patients with carpal tunnel syndrome and controls in ulnar nerve conduction. There were no statistically significant differences in nerve conduction study results or cross-sectional area of the ulnar nerve between patients with carpal tunnel syndrome with and without extramedian symptoms. Conclusions-The cross-sectional areas of the ulnar and median nerves at the wrist are increased in patients with carpal tunnel syndrome. Also, the cross-sectional area of the ulnar nerve is decreased after carpal tunnel release.