Volar Dislocation of the Extensor Carpi Ulnaris Tendon on Magnetic Resonance Imaging Is Associated With Extensor Digitorum Communis Tendon Rupture in Rheumatoid Wrists Takeshi Egi, MD, Kentaro Inui, MD, PhD, Tatsuya Koike, MD, PhD, Hitoshi Goto, MD, PhD, Kunio Takaoka, MD, PhD, Kenichi Kazuki, MD, PhD From the Department of Rheumatology, Higashi-Sumiyoshi Morimoto Hospital, Osaka, Japan; and the Department of Orthopaedic Surgery and Department of Metabolism, Endocrinology, and Molecular Medicine, Osaka City University Graduate School of Medicine, Osaka, Japan. Purpose: Extensor tendon rupture in rheumatoid wrists is a common problem and causes immediate dysfunction of the digits. The best treatment for tendon rupture may be prophy- lactic management, although the factors associated with tendon rupture must first be iden- tified. The purpose of this study was to evaluate structures around rheumatoid wrists using magnetic resonance imaging with forearm rotation and to identify factors associated with extensor tendon rupture as indications for prophylactic surgery. Methods: The subjects were 34 patients (40 wrists) with active rheumatoid arthritis. The extensor digitorum communis (EDC) tendons were ruptured in 15 wrists. Magnetic resonance imaging of the wrists was performed in maximally pronated and supinated positions of the forearm. Axial images of the distal radioulnar joints (DRUJs) were selected to evaluate DRUJ synovitis, dorsal tenosynovitis, volar dislocation of the extensor carpi ulnaris (ECU) tendon, sigmoid notch angle, and the radioulnar ratio (RUR) (ie, the degree of DRUJ subluxation). Results: No significant correlations were found between EDC tendon rupture and DRUJ synovitis, dorsal tenosynovitis, or RUR in pronation. Extensor digitorum communis tendon rupture correlated significantly with volar ECU tendon dislocation, sigmoid notch angle, and RUR in supination. Radioulnar ratio correlated significantly with volar ECU tendon disloca- tion only in supination and not in pronation. Thus, DRUJ subluxation was advanced even in the supinated wrist with volar ECU tendon dislocation. As a factor associated with EDC tendon rupture, volar ECU tendon dislocation had 87% sensitivity and 76% specificity. Conclusions: Volar ECU tendon dislocation is associated with increased RUR in supination and EDC tendon rupture. Volar ECU tendon dislocation can thus be considered a factor associated with EDC tendon rupture, and its presence may indicate the need for prophylactic surgical intervention in a subset of rheumatoid arthritis patients. (J Hand Surg 2006;31A: 1454 –1460. Copyright © 2006 by the American Society for Surgery of the Hand.) Type of study/level of evidence: Prognostic II. Key words: Extensor carpi ulnaris, magnetic resonance imaging, rheumatoid arthritis, tendon rupture, wrist. E xtensor tendon rupture in the hand is a common finding in patients with rheumatoid arthritis (RA). 1 Because such ruptures cause immediate dysfunction of the digits, surgical reconstruction is usu- ally required. 2,3 The extensor tendons, however, grad- ually weaken during the course of the inflammatory process involving the tenosynovium of the wrist. 4 Pa- tients with a ruptured tendon do not always recognize 1454 The Journal of Hand Surgery