Abstract
Given the proximity and shared structures of Guyon's canal and the carpal tunnel, compression of the ulnar nerve is a rarely observed but possible complication of carpal tunnel release. In this case report, a patient underwent previous carpal tunnel release and immediately experienced ipsilateral hand weakness in keeping with an ulnar nerve compression syndrome. Clinical, electrodiagnostic, and magnetic resonance imaging findings after carpal tunnel release demonstrated a compression or injury to the deep motor branch of the ulnar nerve not previously present. Subsequent release of Guyon's canal identified a separate compartment of the deep motor branch of the ulnar nerve within the ulnar leaflet of the transverse carpal ligament. After the release of the motor branch from this compartment, the patient experienced recovery from their neuropathic symptoms. This case report outlines the relevant anatomy and clinical data surrounding an anomalous compartment of the deep motor branch of the ulnar nerve.