Compression of the ulnar nerve and spasm of the ulnar artery in Guyon's canal caused by a hypermobile pisiform bone.

We describe compression of the ulnar nerve at Guyon's canal caused by a hypermobile pisiform bone and associated with spasm of the ulnar artery. Treatment included excision of the pisiform bone, and repair of the flexor carpi ulnaris, hypothenar musculature, and periosteum. Postoperatively, the patient reported complete relief of symptoms, which had still been maintained at final follow-up one year later.