Ultrasonographic and functional changes of the ulnar nerve at Guyon's canal after carpal tunnel release.

Objective: To describe morphologic and functional modifications of the ulnar nerve at the wrist in carpal tunnel syndrome (CTS) after carpal tunnel release (CTR). Methods: Ultrasonography was used to study the cross sectional area (CSA) of the ulnar nerve at Guyon’s canal, before and 1 and 6 months after CTR, in 18 CTS patients. A parallel electrophysiological and clinical analysis was also conducted. Results: CSA of the ulnar nerve significantly increased 6 months after CTR. Ten (55%) cases showed abnormal CSA values compared to a control group before surgery and five (28%) at 6 month follow-up. In addition, there were improvements in the motor and sensory ulnar axon recruitment properties and the conduction values in sensory ulnar fibres. Patients with extra-median distribution of paresthesia (4 subjects) were free from symptoms. Conclusions: CTR has a significant effect not only on the anatomical geometry of Guyon’s canal, but also on the morphology and function of the ulnar nerve. Significance: In CTS, high pressure in the carpal tunnel may result in anatomical changes of ulnar nerve, thus causing functional impairment to the ulnar fibres. CTR appears to reverse some of this damage.