Cubital Tunnel Syndrome on MRI: Imaging Findings

The ulnar nerve passes through the cubital tunnel at the medial elbow, a fibro-osseous channel bordered by the medial epicondyle anteriorly, the olecranon posteriorly, and the arcuate ligament of Osborne (cubital tunnel retinaculum) superiorly. The nerve is most vulnerable at the level of Osborne's ligament, where the canal narrows during elbow flexion. Additional sites of compression along the ulnar nerve course include the arcade of Struthers proximally and the flexor carpi ulnaris aponeurosis distally. Electrodiagnostic studies localizing conduction block to the elbow segment confirm the diagnosis.

Cubital tunnel syndrome compresses the ulnar nerve at the elbow and affects both the dorsal cutaneous branch (supplying sensation to the dorsum of the little finger and ulnar ring finger) and the motor branch to the flexor carpi ulnaris, whereas ulnar tunnel syndrome at Guyon's canal at the wrist spares the dorsal cutaneous branch and the flexor carpi ulnaris. Sensory loss on the dorsal ulnar hand therefore points to an elbow-level lesion, while preserved dorsal hand sensation with intrinsic weakness and little finger sensory loss suggests a wrist-level compression, which may be caused by a ganglion cyst, hook of hamate fracture, or ulnar artery thrombosis.

Simple in-situ decompression releases Osborne's ligament and the surrounding fascial constraints without moving the nerve, making it effective for mild-to-moderate disease with the advantage of lower complication rates. Medial epicondylectomy removes the medial epicondyle to eliminate the pulley effect on the nerve during elbow flexion. Anterior transposition relocates the nerve anterior to the medial epicondyle in a subcutaneous, intramuscular, or submuscular plane, reducing tension on the nerve during flexion; submuscular transposition is preferred for cases with nerve subluxation or recurrence after prior decompression. All techniques show comparable outcomes in mild disease, but severe cases with fixed intrinsic weakness have a guarded prognosis regardless of technique.