Carpometacarpal dislocation: an aid to diagnosis

Although the 'true' lateral radiograph of the hand has improved diagnosis of carpometacarpal dislocation, cases can still be missed if only the carpometacarpal joint area is inspected, as overlap of the adjoining joints can make interpretation difficult. Measurement of the angle between the long axis of the second and fifth metacarpal bones on a true lateral radiograph, in cases of fifth carpometacarpal dislocation is advocated, as the carpometacarpal angle is increased compared with controls (38.5 degrees compared with 9.8 degrees). A lesser increase in the carpometacarpal angle is suggestive of subluxation of this joint and this should be examined under anaesthesia.