[Ulnar nerve compression in Guyon's canal by an accessory abductor digiti minimi brevis muscle]

Compression syndromes of the ulnar nerve are more often located proximally in the cubital tunnel than distally in Guyon's canal. In many cases anatomic structures can be found that induce compression. These may be ganglia, tumours, vascular abnormalities, crossing fibrous bands or accessory muscles. The ulnar nerve has therefore to be revised all along its passage through Guyon's canal. When other causes are excluded, it might be necessary to excise an accessory muscle to decompress the ulnar nerve sufficiently.