Anatomy of the Cubital Tunnel and Mechanism of Compression

The ulnar nerve runs down the inner side of the arm and passes through a groove behind the bony prominence of the inner elbow (medial epicondyle). What produces the electric shock when the elbow is knocked is not bone but the ulnar nerve, lying unprotected beneath the skin.

Beyond the groove the nerve passes under a membranous structure known as Osborne's band, between the two heads of a forearm muscle. The groove and this band together form the cubital tunnel.

When the elbow bends, the volume of the tunnel falls markedly and the nerve is both stretched and compressed. Holding the elbow flexed for long periods — on the telephone, sleeping with the arm bent, resting the elbow while driving — therefore aggravates symptoms directly.

The ulnar nerve supplies sensation to the little finger and the inner half of the ring finger and powers the small muscles within the hand. As compression progresses, grip strength and fine finger control deteriorate.

Risk Factors

• Prolonged elbow flexion: sleeping with the arm bent, long telephone calls, working with the elbow propped on a desk
• Repeated pressure on the inner elbow: leaning on hard surfaces, driving, operating machinery
• Previous elbow fracture or dislocation: distortion of the canal, late (tardy) ulnar nerve palsy
• Elbow arthritis, bone spurs, ganglion cysts within the canal
• Subluxation of the nerve out of its groove on flexion, with repeated friction
• Throwing and racquet athletes: repetitive tension on the inner elbow, sometimes with medial collateral ligament insufficiency
• Diabetes, thyroid disease, rheumatoid arthritis
• Smoking and obesity

Symptoms

• Numbness and tingling in the little finger and inner half of the ring finger: sparing of the thumb and index finger distinguishes it from carpal tunnel syndrome
• Symptoms worse with the elbow bent: on the phone, driving, sleeping
• Waking at night, typical in patients who sleep with the arm flexed
• Pain over the inner elbow radiating along the inner forearm into the hand
• Clumsiness: turning keys, doing up buttons, picking up coins, typing
• Reduced grip and pinch strength, dropping objects
• Wasting of the muscles between the fingers in advanced disease, visible as hollowing on the back of the hand
• Claw hand in advanced disease: the ring and little fingers fail to straighten fully
• Froment's sign: the thumb tip flexes when pinching paper, indicating adductor weakness

Making the Diagnosis

Diagnosis rests on history and examination. Symptoms confined to the ulnar nerve territory and aggravated by elbow flexion are highly indicative.

Examination assesses sensation, finger abduction and adduction strength, and grip. Tingling radiating into the hand when the nerve is tapped at the inner elbow (Tinel's sign) and numbness appearing within a minute of full elbow flexion (elbow flexion test) support the diagnosis. The nerve is palpated during flexion and extension to detect subluxation.

Nerve conduction studies localise and grade the compression and distinguish cervical radiculopathy (C8 - T1), thoracic outlet syndrome and compression in Guyon's canal at the wrist. They are the standard preoperative investigation and may be normal in early disease.

Ultrasound shows thickening of the nerve, subluxation and masses within the canal dynamically. Radiographs demonstrate previous fracture, arthritis and bone spurs.

Non-operative Treatment

In mild and moderate cases without muscle wasting, treatment begins non-operatively. A substantial proportion of patients improve markedly with positional measures alone.

• Night splint or soft elbow wrap holding the elbow at 30 - 45 degrees to prevent excessive flexion during sleep: the most effective single measure
• Activity modification: avoiding leaning on the elbow, using a headset, supporting the arm at the desk
• Elbow pad to protect the nerve from direct pressure during the day
• Nerve gliding exercises, performed gently and without pain
• Anti-inflammatory medication for short-term pain control
• Corticosteroid injection is not routinely recommended: benefit is limited and the superficial nerve is at risk
• Review of technique and training load in athletes
• Control of diabetes and thyroid disease
• Response is assessed after 6 - 12 weeks of consistent treatment

General Surgical Risks

• Wound infection
• Bleeding and haematoma
• Risks related to anaesthesia
• Wound healing problems and scar tenderness
• Temporary elbow stiffness

Risks Specific to This Operation

• Injury to branches of the medial antebrachial cutaneous nerve, causing permanent numbness around the scar or a painful neuroma: the commonest complication
• Persistent or recurrent symptoms: renewed scar formation around the nerve is the commonest cause
• Subluxation of the nerve after simple decompression, sometimes requiring revision
• Renewed compression of the nerve in its new bed after transposition
• Tenderness over the inner elbow when leaning on it
• Permanent muscle wasting and weakness in patients operated late
• Ligament insufficiency and elbow instability after medial epicondylectomy
• Complex regional pain syndrome: rare