Ulnar Nerve Injury

Anatomy of the ulnar nerve

The ulnar nerve arises from the lower nerve roots in the neck (C8 and T1), travels down the inner arm, passes behind the bony bump on the inside of the elbow (the medial epicondyle) through the cubital tunnel, runs down the forearm, and enters the hand through Guyon's canal at the wrist. It provides feeling to the little finger and half of the ring finger and controls most of the small muscles of the hand that allow fine movements and grip.

Hitting the "funny bone" is actually hitting the ulnar nerve where it is exposed at the elbow.

Causes

At the elbow (cubital tunnel syndrome)

Cubital tunnel syndrome is the second most common nerve entrapment after carpal tunnel syndrome. Causes include:

• prolonged elbow bending, such as holding a phone or sleeping with bent arms, which stretches and compresses the nerve
• leaning on the elbow on desks, armrests or car windows
• the nerve slipping over the bony bump with movement
• arthritis, bone spurs and cysts
• previous fractures or dislocations of the elbow

At the wrist (Guyon's canal)

• cycling (handlebar palsy) and pressure from tools
• ganglion cysts
• fractures of the hamate bone
• prolonged use of crutches or walkers

Direct injury

• cuts to the forearm or wrist
• elbow fractures and dislocations
• pressure during surgery or prolonged immobilization

Other causes

• diabetes and other neuropathies
• nerve root compression in the neck (cervical radiculopathy)
• thoracic outlet syndrome

Symptoms

• numbness and tingling in the ring and little fingers, often worse at night or with the elbow bent
• aching on the inner side of the elbow
• weakness of grip and pinch
• clumsiness with fine tasks: buttoning, typing, using keys
• difficulty spreading or crossing the fingers
• muscle wasting between the thumb and index finger and on the side of the hand
• in severe cases, a "claw hand": the ring and little fingers curl

Ulnar vs median nerve (carpal tunnel)

Diagnosis

• examination: sensation, strength, muscle wasting, Tinel's sign at the elbow, the elbow flexion test, Froment's sign (pinch weakness)
• nerve conduction studies and EMG: confirm the location and severity
• ultrasound or MRI: look for nerve swelling, cysts or other structures pressing on the nerve
• X-rays: for bone spurs, arthritis or old fractures
• neck MRI if a nerve root problem is suspected

Treatment

Non-surgical treatment for mild cases

• avoid leaning on the elbow, and use padding on hard surfaces
• avoid prolonged elbow bending: use a headset for phone calls
• night splint or a towel wrapped loosely around the elbow to keep it straighter during sleep
• adjust desk and keyboard height
• padded cycling gloves and changing hand positions
• nerve gliding exercises from a therapist
• NSAIDs for short-term pain relief, following the label dose

Many mild cases improve within 6 to 12 weeks.

Surgery

Considered for persistent symptoms despite 3 months of non-surgical care, weakness or muscle wasting:

• cubital tunnel release: opening the roof of the tunnel to relieve pressure
• anterior transposition: moving the nerve to the front of the elbow
• medial epicondylectomy: removing part of the bony bump
• Guyon's canal release for wrist compression
• nerve repair or grafting for cuts

Outlook

Mild compression usually recovers fully. Numbness often improves after surgery, but long-standing weakness and muscle wasting may not fully recover. Early treatment gives the best results.

Frequently asked questions

What are the symptoms of ulnar nerve injury?

Common symptoms are numbness and tingling in the ring and little fingers, aching on the inner elbow, weak grip, clumsiness with fine tasks and, in severe cases, muscle wasting and curled fingers.

What causes ulnar nerve entrapment?

The most common cause is compression at the elbow from prolonged bending or leaning on the elbow (cubital tunnel syndrome). Pressure at the wrist from cycling or tools, fractures, cysts and arthritis are other causes.

How is cubital tunnel syndrome treated?

Mild cases improve by avoiding elbow pressure and bending, using a night splint and doing nerve gliding exercises. Surgery to release or move the nerve is recommended for persistent symptoms, weakness or muscle wasting.

Can an ulnar nerve injury heal on its own?

Mild compression often improves on its own within weeks to months once the cause is avoided. Severe compression, nerve cuts or long-standing weakness usually need surgery to give the best chance of recovery.

Why does hitting my funny bone hurt so much?

The "funny bone" is the ulnar nerve where it passes close to the skin behind the elbow. A knock compresses the nerve, sending a jolt of tingling and pain into the ring and little fingers. It usually settles within minutes.