Cubital tunnel syndrome

What it is

The ulnar nerve runs from the neck to the hand. At the elbow it passes through a narrow tunnel behind the bony point on the inner side, just under the skin. It supplies feeling to the little finger and half of the ring finger, and powers most of the small muscles of the hand that control fine movements and pinch.

Bending the elbow stretches the nerve and narrows the tunnel; leaning on the elbow presses on it directly. In cubital tunnel syndrome the nerve is squeezed or irritated enough to stop working properly. It is the second most common trapped nerve in the arm after carpal tunnel syndrome.¹

Often no single cause is found. It is more likely after an old elbow injury, with arthritis of the elbow, with long periods spent with the elbow bent, or where the nerve slips over the bone as the elbow moves.

Symptoms

• Tingling or numbness in the little finger and the adjoining half of the ring finger.
• Symptoms brought on by holding the elbow bent: using a phone, reading, driving, or sleeping with the arms curled up. Waking at night with a numb hand is common.
• Aching on the inner side of the elbow.
• Later: a weak grip and pinch, clumsiness with keys, buttons or coins, and thinning of the muscles of the hand, most visibly in the web between thumb and index finger.

How it is diagnosed

The diagnosis is usually clear from your symptoms and an examination of feeling and strength in the hand. Nerve conduction studies, which measure how well the nerve carries signals across the elbow, confirm the site and the severity. An X-ray or ultrasound scan is sometimes added to look for a cause at the elbow. Similar symptoms can occasionally come from the neck or the wrist, and the tests help tell these apart.

Treatment without surgery

If symptoms are mild and come and go, and there is no weakness, it is reasonable to start by taking the pressure off the nerve:

• Avoid leaning on the elbow; pad hard armrests and desk edges.
• Avoid keeping the elbow bent for long: use a headset or speaker for calls, and adjust your chair and keyboard so the elbows are more open.
• At night, keep the elbow fairly straight. A towel wrapped loosely around the elbow, or a soft splint, stops it bending fully while you sleep.

The research on non-operative treatment is limited, but one trial in mild to moderate cases found that simply explaining which positions and movements to avoid reduced symptoms.¹ Give these measures two to three months.

When surgery is advised

• Symptoms that persist despite a proper trial of the measures above.
• Constant numbness.
• Any weakness or muscle wasting in the hand.
• Nerve conduction studies showing significant nerve damage.

A nerve that has been compressed for a long time may not recover fully even after a successful release. This is the main reason not to delay once there is weakness.

The operation

The standard operation is a decompression: through an incision on the inner side of the elbow, the tight tissue forming the roof of the tunnel is divided so the nerve has room. The nerve is left in its natural position.

In some people the nerve is also moved to the front of the elbow (a transposition), for example if it slips out of its groove when the elbow bends, or if the elbow is misshapen after an old injury.

Trials comparing the two found them equally effective, including when the nerve is badly affected.¹ Between 7 and 9 in every 10 people improve after surgery, depending on the study and on how severe the problem was beforehand.^1,2 Because transposition is the larger operation, simple decompression is preferred unless there is a specific reason to move the nerve.

The operation is a day case, under general or regional anaesthetic, and takes about half an hour.

Risks

Serious complications are uncommon, and simple decompression has the lowest complication rate of the available operations.² The figures below are averages from published studies and are a guide only.

• Incomplete recovery. Between 1 and 3 in every 10 people do not improve, most often those whose nerve was badly affected beforehand.^1,2
• Further surgery. In large studies about 2 to 3 in every 100 people have had a second operation, for symptoms that persist or return or for a nerve that slips over the bone after release.^2,3 Some smaller studies with longer follow-up have reported higher figures.⁴
• A tender scar, or a patch of numbness on the forearm just beyond it, from small skin nerves near the incision. This is the commonest minor problem and usually improves.
• Infection or bruising of the wound. Uncommon after simple decompression, and more frequent when the nerve is moved.¹
• Injury to the ulnar nerve itself, and lasting pain and stiffness in the arm (complex regional pain syndrome). Both are rare.

Recovery

These timings are for simple decompression. Recovery after a transposition is slower, and you will be advised individually.

How the nerve recovers

Night-time tingling often eases early. Numbness and strength recover slowly, because nerves heal slowly: improvement can continue for a year or more. Where there was constant numbness or wasting before surgery, the aim is to stop things getting worse, and recovery may be partial.

When to seek help