The cubital tunnel is the fibro-osseous canal through which the ulnar nerve passes posterior to the medial epicondyle of the humerus. The floor of the tunnel is the medial collateral ligament and the flexor-pronator origin, the walls are the medial epicondyle and the olecranon, and the roof is the Osborne ligament (cubital tunnel retinaculum) — a fibrous band connecting the two heads of flexor carpi ulnaris. The tunnel narrows by 55% during elbow flexion.
The cubital tunnel is the second most common site of peripheral nerve compression after the carpal tunnel. Ulnar nerve compression here produces ulnar nerve entrapment (cubital tunnel syndrome) with little finger and ring finger numbness, intrinsic weakness, and eventual clawing of the ring and little fingers. Elbow flexion tightens the Osborne ligament and narrows the tunnel, explaining nocturnal symptoms worse with elbow flexion during sleep. Surgical treatment by in situ decompression, medial epicondylectomy, or anterior transposition moves the nerve out of the cubital tunnel into a protected subcutaneous or submuscular position.
Ulnar nerve compression within the cubital tunnel from prolonged elbow flexion, direct pressure, or elbow valgus produces ring and little finger numbness and tingling, intrinsic weakness causing reduced grip, and eventual fixed clawing; treated by cubital tunnel release with nerve decompression or anterior transposition.
Late-onset ulnar neuropathy years after a childhood lateral condyle fracture that healed in valgus deformity places the ulnar nerve under progressive tension in the cubital tunnel, producing insidious ulnar intrinsic weakness and sensory loss managed by anterior nerve transposition.
