The spectrum of perilunate dislocations: A biomechanic and radiologic perspective

Abstract

The spectrum of perilunate dislocations occurs within a well defined sequential range of perilunate carpal instabilities. An understanding of the biomechanics of this instability continuum allows accurate assessment of bony and ligamentous injuries. Radiographic and CT features of the injury pattern shows the progression of injury and perilunate joint derangement through either the lesser or greater arcs. Perilunate dislocations are the most common carpal dislocation and represent a spectrum of perilunate carpal instabilities because of forced sudden extension, supination and ulnar-deviation of the wrist. Injuries within this spectrum include scapholunate dissociation, perilunate dislocation and lunate dislocation. A progressive injury pattern propagates from the distal radius, around the lunate to the ulnar side of the carpus via either the lesser or greater arcs, thereby consecutively disrupting capsular, ligamentous and osseous structures. Mayfield (1) described 4 distinct but successive stages in extended, supinated and ulnar-deviated cadaver wrists subjected to axial loading. Radiographic and CT findings clearly show the progression of the course of force transmission and subsequent injury. Stage 1 entails scaphoid extension with subsequent scapholunate dissociation with or without scaphoid fracture. Dorsal dislocation of the distal carpal row then occurs in stage 2, described as perilunate dislocation with disruption of the greater (osseous) or lesser (capsulo-ligamentous) arc. Disruption of the lunatotriquetrial or triquetro-capito-hamate ligament then ensues, a stage 3 injury. Finally, the lunate dislocates, usually in the volar direction. True lunate dislocation therefore represents the end stage of the perilunate dislocation progression. Perilunate instability is a progressive injury pattern that results from sudden axial compression of the extended, supinated and ulnardeviated wrist. Four sequential stages result with differentiating radiographic features. Understanding of the mechanism of force transmission around the lunate allows detection of associated injuries within the spectrum of perilunate instability.<br />