Ulnar luxation of the extensor pollicis longus. Anatomic and clinical study

: The authors report five cases of ulnar dislocation of the Extensor pollicis longus caused by rupture of the hood at the metacarpophalangeal of joint the thumb. This rarely described lesion is well known in long fingers but seems to be less common in the thumb and no previous series can be found in the literature. This dislocation gives a deficit on active extension of the metacarpophalangeal joint of the thumb. During trauma of MP, the expansion of abductor pollicis brevis cans be damaged which provokes ulnar dislocation of EPL. An anatomical study of this region is reported by the authors. 10 dissections on fresh or prepared cadavers were performed with two series of slices of all of the extensor apparatus on the MCP. The hood of the MCP has two superposed planes: one is superficial with transverse fibers which run over the joint from the Abductor to the adductor with the EPL getting through it and a deep plane composed of the EPB and the capsule. Diagnosis is made on clinical observation. The patient has partial deficit of extension of the MCP with a history of old thumb trauma. EPL is active and palpable under the skin. On the MCP it is ulnarly dislocated and lesion front of the rotation center. Dislocation can be reduced manually by a skin pinch on the dorsal part of the MCP. Extension is then possible and complete. This lesion is rare, as we have found only five patients reported between 1984 and 1991. Two patients presented an isolated dislocation of the EPL due to a lesion of the superficial plane.(ABSTRACT TRUNCATED AT 250 WORDS)