Re: Irreducible dorsal dislocation of the index carpometacarpal joint

Abstract

A 40 year-old man was admitted as an emergency after a fall on his dominant right hand in which he struck the ground with the dorsum of his hand with his wrist flexed. He had marked swelling of the dorsum of the hand at the base of the index metacarpal and internal rotation of the index finger, with a dorsal bony prominence and tenderness over the index metacarpal base. Motion of this finger and dorsiflexion of the wrist were both restricted and painful. X-rays of the hand revealed an isolated dorsal dislocation of the index carpometacarpal joint without fracture (Fig 1). Several attempts at closed reduction failed. Under local anaesthesia, through a dorsal incision, the radial extensors of the wrist were isolated. The extensor carpi radialis brevis (ECRB) tendon was found to be interposed between the base of the index metacarpal and the trapezoid (Fig 2). The tendon was retracted to the ulnar side and the joint reduced. A plaster cast only was applied for 4 weeks, following which he had 3 weeks of grip-strengthening exercises. At 2 months, he was pain free, had normal ranges of motion of his wrist and finger joints and returned to work. At 2 years, he was able to perform strenuous manual work without any discomfort.The index carpometacarpal joint is a structurally stable joint because of its intrinsic bony stability through interlocking articular surface anatomy, strong volar, dorsal and intermetacarpal ligaments and periarticular tendinous support (Van der Lei and Klasen, 1992). This dislocation is rare, with only two previous reports in the English literature (Carnerio and Rancatore, 2000;Ho et al., 1987). It also requires considerable energy, as a consequence of which it is often associated with concomitant fractures of either the metacarpal base or the carpal bones (Lawlis and Gunther, 1991). The probable mechanism of injury in this case was force transmission along the index metacarpal when the head of this bone struck the ground, with hyperflexion of the carpometacarpal joint levering out the base of the metacarpal dorsally. The ECRB tendon lies over the joint just proximal to its insertion, mainly into the third metacarpal base. ECRB entrapment is more likely when an internal rotatory component is added to the metacarpal dislocation (Mehara and Bhan, 1993). Fig 1 Preoperative anteroposterior and lateral X-ray views of the patient's hand. Dorsal dislocation and internal rotation of the index metacarpal are seen. Fig 2 Intra-operative photograph showing the interposed ECRB tendon between index metacarpal base and trapezoid.