Mechanical strain at the pisotriquetral joint.

Pain and tenderness on the palmar and ulnar aspects of the wrist in the area of the pisiform bone is fairly common. Chronic pain in the pisiform area may be due to tendinitis of the insertion of the flexor carpi ulnaris, bony fractures or osteoarthrosis of pisotriquetral joint which is the second most common degenerative arthritis in wrist after the scaphotrapezial osteoarthrosis (Fischer, 1988, Radiologe 28:338-344). Subperiostal excision of pisiform bone is customarily performed after unsuccessful initial non-operative treatment (Carroll and Coyle, 1985, J. Hand Surg. 10:703-707; Johnston and Tonkin, 1986, Clin. Orthop. 210:137-142; Nüesch et al., 1993, Handchir. Mikrochir. Plast. Chir. 25:42-45). Although the postoperative results seem to be rather good, possible malfunction based on excision has not been considered previously by investigators. The aim of this study was to improve our understanding of the role of the pisiform and the pisotriquetral joint in the transfer of forces within the carpus. In a first part we examined 112 pisotriquetral joints by qualitative, quantitative and densitometrical analysis of joint surfaces. Secondly, mechanical tests were performed to investigate the distribution of forces within pisiform and the pisotriquetral joint. The results demonstrate that the pisiform mechanically contributes to the stability of the ulnar column of the wrist. The pisiform, and its unique anatomical holding mechanism, discharges two main functions. It holds the triquetrum in a correct position and prevents its subluxation even in extreme extension. Furthermore, it acts as a fulcrum (hypomochlion) while transducing powerful forearm forces to the hand. The excision of pisiform should be reconsidered.