[Dislocation of the thumb extensor tendons: an anatomical, clinical study and new classification]

The authors report on 11 cases of ulnar dislocation of the extensor pollicis longus (EPL) due to rupture of the dorsal aponeurosis at the thumb metacarpophalangeal (MCP) joint. This condition is rare. By performing a descriptive study of this injury, we were able to establish a classification system for thumb extensor tendon dislocation. The series included 11 patients with a mean age of 27years. All patients presented with either varus or rotational thumb injury. This resulted in an active extension deficit in the thumb MCP joint with EPL dislocation behind the MCP. Surgery was required in all cases. We defined three different injury presentations: 1) dissociated form with isolated EPL dislocation, but the EPB still in place; 2) complete form with dislocation of both tendons on the ulnar side of the MCP; 3) dissociated or complete form associated with a severe sprain of the lateral collateral ligament of the thumb MCP joint. The surgical treatment was adapted to each case. A classification into three types of dislocation of the extensor tendons at the MCP joint of the thumb was established. This rare condition must be identified at the time of thumb MCP joint injury and also when harvesting the EPB. This new classification system has a diagnostic and therapeutic role as it precisely describes the dislocation type and the resulting damage. Only a surgical treatment can produce good repairs.