Ulnar nerve entrapment most often occurs at the elbow (cubital tunnel) and less commonly at the wrist (Guyon's canal). Numbness in the ring and little fingers and weakness of the hand are typical symptoms.
What is ulnar nerve entrapment?
At the inner side of the elbow, the ulnar nerve runs very close to the skin — the spot commonly known as the "funny bone" — and it powers most of the muscles responsible for fine hand movements. Entrapment occurs at two main sites:
- Cubital tunnel syndrome (at the elbow): The second most common nerve entrapment in the arm. Keeping the elbow bent for long periods (talking on the phone, leaning on the elbow, sleeping with the arm bent), old elbow fractures and slipping of the nerve out of its groove are risk factors.
- Guyon's canal syndrome (at the wrist): Less common; it can be caused by repeated pressure on the palm, as in cycling, or by masses inside the canal such as a ganglion cyst.
Symptoms
- Numbness and tingling in half of the ring finger and the little finger
- Pain on the inner side of the elbow (cubital tunnel)
- Symptoms that worsen when the elbow is kept bent
- Weakness of the hand muscles; difficulty buttoning or opening jars
- Wasting of the muscles on the back of the hand and clawing of the fingers in advanced cases
Diagnosis
Examination and EMG determine whether the compression is at the elbow or the wrist. When needed, ultrasound, elbow X-rays or MRI are used to assess structures pressing on the nerve. Distinguishing it from a cervical disc herniation is important.
Treatment Approach
- Non-surgical treatment: In mild cases, avoiding prolonged elbow bending, not leaning on the elbow, a night splint that keeps the elbow straight and medication are used.
- Surgery: For persistent symptoms, weakness or muscle wasting, the nerve is released (decompression). If the nerve slips out of place with elbow movement, it may be moved to the front of the elbow (transposition). Any mass compressing the nerve in Guyon's canal is removed.
Sensory symptoms improve after surgery in most patients, while recovery of muscle strength can take longer, and recovery may be limited after long-standing, severe compression. Early assessment is therefore important.