Ulnar nerve

a nerve originating from the brachial plexus and innervating the skin on the front and back of the medial part of the hand, some flexor muscles of the arm, and many muscles of the hand and the elbow joint and many joints of the hand. also, see ulnar nerve.

2. Pathology

An entrapment neuropathy of the ulnar nerve may occur in several ways. Most commonly the compression occurs near the elbow or wrist and it is rarely seen in the forearm.

At the level of the cubital tunnel, where the ulnar nerve extends through a fibro-osseous canal formed by the medial epicondyle and an aponeurotic band bridging the dual origin of the flexor carpi ulnaris muscle, compression leads to the cubital tunnel syndrome. Among the causes of such compression are trauma, progressive cubitus valgus deformity and masses. Patients may have sensory deficits and weakness of the flexor carpi ulnaris muscle, flexor digitorum profundus muscle of the fourth and fifth fingers, and intrinsic hand muscles. Although axial radiographs may reveal narrowing of the cubital tunnel (related in part to osteophytosis), MR imaging is far more effective for evaluating this syndrome. MR imaging abnormalities include displacement of the ulnar nerve, a soft tissue mass, and enlargement and increased signal intensity in the compressed nerve.

An entrapment neuropathy termed Guyons canal syndrome or ulnar tunnel syndrome may occur in the wrist where the ulnar nerve enters the palm through the canal of Guyon or ulnar tunnel. The most frequent causes of ulnar nerve entrapment in Guyon's canal are ganglia and accidental, occupational or recreational (bicycling) trauma. Fractures of the hook of the hamate may also lead to such entrapment.

A type of double crush syndrome results from concomitant entrapment of the ulnar nerve with disease of the lower cervical spine or the thoracic outlet syndrome.

DR