What is cubital tunnel syndrome?

Cubital tunnel syndrome is compression of the ulnar nerve as it passes behind the inner side of the elbow, the spot known as the "funny bone". It causes numbness and tingling in the ring and little fingers and, in time, weakness of the hand. It is the second most common nerve compression in the arm after carpal tunnel syndrome.

Mild cases improve with simple measures such as night splints and avoiding pressure on the elbow. Persistent symptoms, or any weakness or muscle wasting, need assessment, as surgery to release the nerve protects hand function.

Symptoms

The ulnar nerve runs through a narrow tunnel behind the bony point on the inner side of the elbow (the medial epicondyle). Bending the elbow stretches the nerve and raises pressure inside the tunnel several-fold. Over time, repeated or sustained bending reduces blood flow to the nerve and affects its function.

Risk factors include:

• Sustained elbow bending, at work, on the phone or during sleep

• Leaning on the elbow, for example on a desk or car door

• Repetitive gripping and throwing sports

• Musical instruments held with the elbow bent, including violin, viola and guitar

• A nerve that slips over the bony point when the elbow bends

• A previous elbow fracture, arthritis or bony spurs

• Diabetes, which makes nerves more vulnerable to pressure

• Male sex, with men affected at about twice the rate of women

Causes and who is at risk

The ulnar nerve runs through a narrow tunnel behind the bony point on the inner side of the elbow (the medial epicondyle). Bending the elbow stretches the nerve and raises pressure inside the tunnel several-fold. Over time, repeated or sustained bending reduces blood flow to the nerve and affects its function.

Risk factors include:

• Sustained elbow bending, at work, on the phone or during sleep

• Leaning on the elbow, for example on a desk or car door

• Repetitive gripping and throwing sports

• Musical instruments held with the elbow bent, including violin, viola and guitar

• A nerve that slips over the bony point when the elbow bends

• A previous elbow fracture, arthritis or bony spurs

• Diabetes, which makes nerves more vulnerable to pressure

• Male sex, with men affected at about twice the rate of women

How is cubital tunnel syndrome diagnosed?

Diagnosis combines examination with nerve tests. At your consultation I examine the elbow, the hand muscles and sensation, and check the neck and wrist for other sites of compression. Key findings include:

• Tingling when the nerve is tapped behind the elbow

• Symptoms reproduced by holding the elbow fully bent for one minute

• Weakness spreading the fingers apart or pinching

• Whether the nerve slips over the bony point as the elbow bends

I arrange tests to confirm the diagnosis and measure severity:

• Nerve conduction studies and electromyography (EMG) show where the nerve is compressed and how much damage there is. They guide the timing of surgery.

• Ultrasound shows the nerve's size, its movement and any cause of pressure such as a cyst.

• X-rays where there is arthritis or a previous fracture.

These tests also exclude conditions that cause similar symptoms: a trapped nerve in the neck, compression at the wrist (Guyon's canal) and thoracic outlet syndrome.