Cubital Tunnel Syndrome
Cubital tunnel syndrome is caused by pressure on the ulna nerve, as it passes through the “cubital tunnel”, on the inner side of the elbow.
It is similar in nature to carpal tunnel syndrome, but a different nerve is compressed at a different site.
The ulna nerve transmits sensory information from the little finger and half the ring finger to the central nervous system. The ulna nerve also transmits signals from the central nervous system to many of the fine muscles in the hand.
The cubital tunnel
The ulna nerve passes behind the medial epicondyle (inner bony bump) of the elbow, where it is held in place by a firm fibrous band. If there is increased pressure around the nerve, it will tend to be compressed in this region.
The first symptom is tingling in the little and ring fingers, which tends to occur when the elbow is in a flexed position. This is because elbow flexion narrows the cubital tunnel. Patients may wake with a sense of numbness in the hand, and this must be differentiated from carpal tunnel syndrome.
As the problem progresses, the patient may loose feeling in the little finger. There may also be pain radiating down the inner aspect of the forearm.
With further progression, the patient will loose power in the hand, as the fine muscles loose their nerve supply. Finally, there will be “clawing” of the ring and little finger when the fine muscles are so weak that they cannot control the posture of the ring and little fingers.
Other problems with similar symptoms
Similar symptoms may arise from different problems. Similar nerve pathways may be affected in the wrist, thoracic outlet or the neck. One of the characteristic findings in cubital tunnel syndrome is that elbow flexion worsens the feeling of tingling or numbness in the hand.
Supportive tests are either physiological or anatomical. Physiological tests include nerve conduction studies, which look at how fast the nerve can conduct impulses at various levels. Delay at the elbow level implies a problem here but does not specify that the problem is compression. Nerve conduction tests are often normal in mild cubital tunnel syndrome. When the nerve conduction studies become positive, often the clinical problem has become quite marked. Nerve conduction studies may remain abnormal for a number of months even after successful decompression and even after symptoms have improved.
Anatomical tests look at the shape of the ulna nerve in the cubital tunnel. These include ultrasound and MRI. An ultrasound performed by a musculoskeletal radiologist is a very useful investigation. As a dynamic test, it will also pick up an abnormal movement of the nerve (subluxation).
- Splints Night extension splinting will successfully treat early cubital tunnel syndrome in 70% of patients, if they are able to continue the treatment for 3 months.
- Steroid injections It is my preference to avoid steroid injections in this condition. There is a small chance of complete nerve palsy following injections around the nerve at the elbow level. This is a complication best avoided.
- Surgery Surgery may be considered if sensory symptoms are not settling after night splinting, or if constant numbness in the hand is present. Surgery should be considered if there is muscle weakness in the hand.
- Simple decompression – “unsquashing” the nerve is successful in 90% of patients.
- Transposition – this slighlty more aggressive surgery may be considered if the nerve is unstable, severely compressed or if the nerve is being compressed from the inside-out. Essentially, the nerve is gently freed from surrounding structures and swung forwards, where it is stabilised under muscle or fat, depending on the circumstances.
- Nerve transfer – this may be considered as an additional procedure in more severe cases. Where there is wasting of the muscles in the hand present for less than a year, a “spare” nerve may be redirected into the muscle part of the ulna nerve in the forearm. This can resuscitate the muscles, which will otherwise disappear permanently after 18 months of wasting.
After surgery, elbow stretches are encouraged early on. It is important that the nerve is kept moving through its surrounding tissues, so that adhesions do not form. If transposition surgery is performed, a sling is used to help protect the area from accidental bumps. After 3-4 weeks, the sling is discarded and strengthening begins. Usually the elbow feels pretty normal after 6-8 weeks.
The speed of recovery of feeling and strength in the hand will depend on how bad the problem was to begin with. Where there is complete numbness in the little finger and the muscles are wasted (shrunken) improvements will continue for more than a year after the surgery.