Dorsal Wrist Extrinsic Carpal Ligament Injury Exacerbates Volar Radiocarpal Instability After Intra-Articular Distal Radius Fracture

BACKGROUND: Volar radiocarpal instability is often seen after loss of fixation of volar lunate facet fragments. The pathogenesis of post-traumatic volar radiocarpal instability is poorly understood. The purpose of this study was to determine if injury to the dorsal wrist extrinsic carpal ligaments contributes to volar radiocarpal instability. METHODS: Six matched pairs of cadaveric upper extremities were tested using a dynamic hand testing system. In group 1, the intact wrist, the wrist with a volar lunate facet fracture, and the fractured wrist after 500 cycles of grip were tested. In group 2, in addition to the intact and fractured wrist, the fractured wrist with the dorsal extrinsic carpal ligaments cut and the fractured wrist with the dorsal extrinsic carpal ligaments cut after 500 cycles of grip were also tested. Volar-dorsal displacement of the lunate was measured from 45° wrist flexion to 45° wrist extension in 22.5° increments with the wrist flexors/extensors loaded for each condition. RESULTS: Volar lunate translation did not significantly increase after the volar lunate facet fracture alone, and was not evident to a significant extent until the dorsal wrist extrinsic carpal ligaments were cut. Further instability of the lunate occurred after grip cycling only with the dorsal extrinsic capsular ligaments cut. CONCLUSIONS: Injury to the dorsal wrist extrinsic carpal ligaments exacerbates volar radiocarpal instability. Unrecognized dorsal sided injury may be a contributing factor to why stable fixation of volar lunate facet fragments remains problematic after volar plating of intra-articular distal radius fractures with displaced volar lunate facet fragments.