REVIEW ARTICLE Traumatic Thumb Carpometacarpal Joint Dislocations B. Bosmans, MD, M. H. J. Verhofstad, MD, PhD, T. Gosens, MD, PhD Isolated traumatic dislocation of the thumb carpometacarpal joint, also called the trapeziometacarpal joint, is a rare injury. Controversy still exists concerning which ligaments are the true key stabilizers for the joint and therefore need to be damaged to result in dislocation, and optimal treatment strategies for thumb carpometacarpal joint dislocations are the subject of continuing debate. We give a review of the literature concerning traumatic dislocations of the carpometacarpal joint of the thumb and propose a treatment algorithm. (J Hand Surg 2008;33A:438–441. Copyright © 2008 by the American Society for Surgery of the Hand.) Key words Carpometacarpal, dislocation, pathophysiology, thumb, treatment algorithm. A PURE TRAUMATIC DISLOCATION of the first carpometacarpal joint is very rare, in contrast with the fracture-dislocation variant, the so-called Bennett fracture. Carpometacarpal dislocation of the thumb accounts for less than 1% of all hand injuries. 1 It usually results from axial loading with flexion of the thumb metacarpal base that forces the joint to dislocate in a dorsal direction. 2,3 Because the volar ligaments are very strong, avulsion of the metacarpal base is usually seen. Although for years the volar oblique ligament has been believed to be the key stabilizer of the thumb carpometacarpal joint, 4 controversy concerning which ligaments are damaged in joint dislocation and which ligaments are the true key stabilizers for joint stability still exists. 5 Optimal treatment strategies for thumb carpometacarpal joint dislocations are still a subject of debate. Strategies have ranged from closed reduction and immobilization in a thumb plaster cast to closed or open reduction and temporary fixation using K-wires with or without reconstruction of capsule and ligaments. 6,7 This article aims to review the relevant literature concerning traumatic dislocation of the carpometacarpal joint of the thumb and its treatment. ANATOMY OF THE THUMB CARPOMETACARPAL JOINT Management of dislocations of the thumb carpometacarpal joint in a proper way requires a fair understanding of its anatomy and function. Several authors have reported on the specific characteristics of the thumb carpometacarpal joint regarding its surfaces and ligaments. Since as early as 1742, when Weitbrecht (quoted by Kaplan 8 ) reported on 4 ligaments around the thumb, the anatomy of the thumb carpometacarpal joint has been studied. It has been called a saddle joint: the trapezium is convex on anteroposterior views and concave on lateral views, whereas the metacarpal is the opposite. 9,10 This unique configuration provides a wide range of motion varying from abduction to opposition while the joint remains stable. The thumb can thus withstand loading and yet allow mobility, resulting in powerful pinching and grasping. This is achieved by means of the so-called screw- home torque mechanism. 5 When the thumb is moved into opposition, a slight internal rotation of the metacarpal takes place and the dorsoradial ligament tightens. At the same moment, the volar beak of the thumb metacarpal is compressed into its recess in the trapezium and the joint gains articular congruence. As a result, a dynamic force couple (ie, abducting force through the abductor pollicis longus in combination with tension on the dorsal ligament and locking of the volar beak resulting in articular congruence) for stability is created and the carpometacarpal joint is converted from an incongruent lax joint in the static resting position to a congruent rigid and stable joint in opposition. Normal function of the carpometacarpal ligaments in this situation is essential. PATHOPHYSIOLOGY IN THUMB CARPOMETACARPAL JOINT DISLOCATION In the late 1960s, the anterior oblique ligament was considered to be the key stabilizer of the thumb carpometacarpal joint. 4 This observation was subsequently debated in the following years by Harvey and Bye 11 and Pagalidis et al 12 who respectively proposed that the posterior From the Department of Surgery and the Department of Orthopaedic Surgery, St. Elisabeth Hospital, Tilburg, The Netherlands. Received for publication October 3, 2007; accepted in revised form November 26, 2007. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Corresponding author: B. Bosmans, MD, St. Elisabeth Hospital, Hilvarenbeekseweg 60, 5022 GC Tilburg, The Netherlands; e-mail: Bas_Bosmans@hotmail.com. 0363-5023/08/33A03-0024$34.00/0 doi:10.1016/j.jhsa.2007.11.022 438  ©  ASSH  Published by Elsevier, Inc.