Cubital tunnel syndrome is entrapment of the ulnar nerve typically at the elbow. It is the second commonest cause of nerve entrapment in the body (the commonest cause is carpal tunnel syndrome with entrapment of the median nerve). The typical symptoms are of numbness and tingling in the ring and little fingers and on the little finger side of the palm. It may be associated with weakening of the muscles, and sometimes wasting (thinning) of the small muscles in the hand and in time contractures of the ring and little fingers may develop. Typically the onset is gradual, starting with numbness and tingling, particularly at night, and it may then become continuous. Occasionally the onset may be very sudden often for no obvious reason. Some patients present only with weakness in the hand and others only with numbness but commonly there is a combination, particularly as the condition progresses.
- The ulnar nerve originates from the medial cord of the brachial plexus and runs inferior to the posteromedial aspects of the humerus, passing behind the medial epicondyle (in the cubital tunnel) at the elbow where it is exposed for several centimetres.
- It then enters the anterior compartment of the forearm through the two heads of flexor carpi ulnaris and runs alongside the ulna bone.
- It continues distally alongside the ulnar artery deep to the flexor carpi ulnaris muscle.
- It enters the palm of the hand, passing with the ulnar artery superficial to the flexor retinaculum of the hand via the ulnar canal (Guyon’s canal).
Causes of ulnar nerve disorders:
- The ulnar nerve can be damaged by dislocation or fracture dislocation of the elbow and can be compressed by those who habitually lean on their elbows.
- It may be associated with medial epicondylitis (golfer’s elbow).
- The nerve can become entrapped in the cubital tunnel of the elbow during heavy manual work or following a previous poorly healed supracondylar fracture of the humerus or due to osteophytic encroachment in osteoarthritis.
- One study found that over half of a group of 91 patients labelled ‘idiopathic’ were found to have a specific cause after careful ultrasound evaluation.
- Causes of compression of the ulnar nerve at the wrist include aneurysm of the ulnar artery, thrombosis, synovial inflammation and ganglia, or by repeated trauma at work.