Ulnar nerve compression at the arch of origin of the adductor pollicis muscle.

The motor branch of the ulnar nerve can be compressed by the arch of origin of the adductor pollicis muscle. There can be a well-defined band of tissue either at the point where the nerve crosses the third metacarpal or where it penetrates the adductor muscle. In over half of the cadaver hands studied no arch was demonstrated. Clinically these patients present with obvious atrophy of the first dorsal interosseous and adductor muscle. Usually pain is not a prominent symptom. This type of ulnar nerve compression neuropathy is present in less than 1% of those ulnar neuropathies that occur at the wrist and hand.