SCIENTIFIC ARTICLE Osteochondroma of the Capitate Causing Rupture of the Extensor Digiti Minimi: Case Report Nirav R. Shah, MD, Mark Wilczynski, MD, Richard Gelberman, MD Osteochondromas usually arise from the metaphyses of long bones. Involvement of the carpal bones is extremely rare. We report a case of an osteochondroma originating from the dorsal capitate in a 51-year-old man. Attritional rupture of the extensor digiti minimi tendon resulted from mechanical irritation as it coursed over the mass. Surgical excision of the mass with tendon transfer of the extensor digiti minimi was subsequently performed. (J Hand Surg 2009;34A:46–48. Copyright © 2009 by the American Society for Surgery of the Hand. All rights reserved.) Key words: Capitate, extensor digiti minimi, osteochondroma. W HETHER SOLITARY OR associated with multi- ple hereditary exostosis, most osteochon- dromas arise from the metaphyseal surfaces of long bones. Solitary osteochondromas of the carpus are extremely rare with only 13 cases previously de- scribed. 1–13 Of these, only 3 were specific to the capi- tate. 1–3 To date, no case of extensor tendon rupture attributed to a dorsal osteochondroma has been de- scribed. We report an unusual case of a large dorsal osteochondroma of the capitate associated with attri- tional rupture of the extensor digiti minimi (EDM) tendon. CASE REPORT A 51-year-old, right-handed man presented with a 9-year history of persistent pain and dorsal mass of the right central wrist. Four years prior, an outside surgeon identified an injury to the scapholunate ligament with an associated dorsal wrist mass. Excision of the mass, dorsal capsulodesis, and radial styloidectomy were rec- ommended. The patient refused surgery. During the interval, the mass gradually enlarged, and the dorsal wrist pain persisted. Weeks prior to presen- tation, the patient felt a painful “pop” on the dorsum of the wrist while lifting heavy boxes, and active extension of the small finger was no longer possible. On physical examination, a prominence of the dorsal carpus was apparent (Fig. 1). Tenderness to palpation was elicited over the mass itself as well as over the scapholunate and lunotriquetral joints. Scaphoid shift maneuver produced a palpable “clunk” with associated dorsoradial wrist pain. Active motion of the involved wrist was from 25° of extension to 65° of flexion. The contralateral wrist demonstrated 80° of active extension and 70° of active flexion. No independent EDM func- tion could be elicited. Fluoroscopic evaluation revealed a large osseous mass protruding from the dorsal aspect of the wrist. Dorsal intercalated segment instability with a scapholu- nate angle of 85° and static scapholunate diastasis was also appreciated. Magnetic resonance imaging (MRI) showed cortical and trabecular continuity between the mass and the capitate. An associated large, loose body was seen directly overlying the capitate. A rupture of the EDM tendon was visualized as it coursed immediately adja- cent to the mass (Fig. 2). In addition, marked tendonitis of the fourth and sixth dorsal wrist compartments and a tear of the scapholunate ligament with associated dorsal intercalated segment instability deformity were identified. With a presumptive diagnosis of osteochondroma of the capitate, the patient had surgery to resect the prom- From the Department of Orthopaedic Surgery, Washington University School of Medicine, Saint Louis, MO. Received for publication May 12, 2007; accepted in revised form August 6, 2008. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Corresponding author: Nirav R. Shah, MD, Department of Orthopaedic Surgery, Washington University School of Medicine, Campus Box 8233, 660 South Euclid Avenue, Saint Louis, MO 63110; e-mail: shahn@wudosis.wustl.edu. 0363-5023/09/34A01-0008$36.00/0 doi:10.1016/j.jhsa.2008.08.004 46  ©  ASSH  Published by Elsevier, Inc. All rights reserved.