Compression of median nerve at elbow.

A 46-year-old man was admitted to St Helier Hospital, Carshalton, for treatment of primary hypercholesterolaemia. He was observed to have considerable wasting of the muscles of the left thenar eminence and probable wasting of the left forearm. On direct questioning he admitted that he had had some weakness of the left hand for several years but denied sensory symptoms. Neurological examination showed gross weakness of the left thumb with wasting of abductor pollicis brevis, flexor pollicis brevis, and possibly flexor carpi radialis. Perception of sharp and blunt in the pulp of the left index finger was diminished, but sensation in the hand was otherwise normal. There were no localised areas of tenderness in the arm or hand. Investigations included normal radiographs of the chest, elbows, and cervical spine. No supracondylar spurs were present. Electromyography suggested compression of the median nerve at the level of the elbow and it was decided to explore this region. With a tourniquet on the upper arm a 10-cm Z-shaped incision was made over the anterior aspect of the elbow and the bicipital aponeurosis divided. The median nerve was identified and traced along its course. A shiny white ligamentous band 3 mm in diameter was found lying parallel with, but separate from, the upper border of pronator teres and passing from the medial epicondyle of the humerus to just below the tuberosity of the radius. This band passed across both the median nerve and the brachial artery and tightly constricted the nerve (see figure). The band was divided and excised to release the nerve. Histological examination of the band showed normal ligamentous tissue.