CASE REPORT Compression of the ulnar nerve and spasm of the ulnar artery in Guyon’s canal caused by a hypermobile pisiform bone MICHEL SAINT-CYR 1 & HAROLD E. KLEINERT 2 1 Department of Plastic Surgery, University of Texas Southwestern Medical Center, Dallas, 2 Department of Surgery, Division of Hand Surgery, University of Louisville School of Medicine, Louisville, USA Abstract 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. Key Words: Ulnar nerve, Guyon’s canal, compression, hypermobile, pisiform Introduction Since Guyon’s first anatomical description of the ulnar tunnel in 1861 and Hunt’s definition of ulnar neuritis in 1908, various causes of compression of the ulnar nerve at the wrist have been reported. Carpal ganglia (29% to 34%), and occupational neuritis (24%), are the most common, and the numerous other causes include occupational trauma, anomalous muscle bellies, fractures, dislocations, giant cell tumours, lipomas, schwannomas, vascular anomalies, and thrombosis of the ulnar artery or vein [1,2]. In this case report we describe the history and treatment of an ulnar nerve compressed at Guyon’s canal by an unstable pisiform bone and associated with spasm of the ulnar artery. Case report A 41-year-old right-handed female warehouse worker presented with an 11-month history of right ulnar-sided wrist pain that persisted despite conser- vative treatment. She initially described a painful popping sensation on the volar ulnar aspect of her wrist after an overhead heavy gripping manoeuvre at work. The patient had been evaluated by four physicians (one primary care physician and three hand surgeons) before she consulted our hand care centre. She had also had an unsuccessful trial of conservative treatment consisting of six months of 24-hour splinting, non-steroidal anti-inflammatory drugs and injection of steroids into the pisotriquetral joint and at the insertion of the flexor carpi ulnaris tendon. Pain over the pisiform bone and intermittent numbness in the small and ulnar ring fingers was aggravated by heavy lifting and gripping. No piso- triquetral arthritis (Figure 1) was shown on plain radiographs and magnetic resonance imaging of the wrist did not show any compressive masses. A bone scan showed mild swelling in the distal ulnar region, compatible with degenerative changes. Ulnar nerve conduction studies showed motor and sensory ulnar mononeuropathy at Guyon’s canal. Motor nerve conduction latency at the wrist was 2.6 ms (normal limit 3.1) whereas distal sensory latency at the wrist was 3.1, with a sensory nerve conduction velocity of 45.1 m/s at the right wrist level compared with 50 m/s for the left unaffected wrist. The above elbow ulnar nerve motor conduction velocities were 61.8 m/s and 63.1 m/s for the right and left sides, respectively. Electromyography showed that com- pound muscle action potential amplitudes were reduced on the right side compared with the left, when recorded on the adductor digiti minimi muscle. Correspondence: Michel Saint-Cyr, MD, FRCS (C), Department of Plastic Surgery, UT Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, Texas 75390-9132, USA. Tel: 214-648-7960. Fax: 214-648-6776. E-mail: michel.saint-cyr@utsouthwestern.edu Scand J Plast Reconstr Surg Hand Surg, 2008; 42: 215Á217 (Accepted 21 June 2006) ISSN 0284-4311 print/ISSN 1651-2073 online # 2008 Informa UK Ltd. (Informa Healthcare, Taylor & Francis As) DOI: 10.1080/02844310601029944