Carpal instability associated with fracture of the distal radius. Incidence, influencing factors and pathomechanics.

134 fractures of the distal radius in 132 patients are reviewed to determine the incidence and influencing factors of coexisting carpal in stability. By measurement and analysis of the changes in carpal angles and joint spaces, carpal instability was discovered in 41 fractures, an incidence of 30.6%. Six patterns of instability were observed, including dorsal intercalated segmental instability (DISI), scapholunate dissociation, dorsal and palmar translocations, volar intercalated segmental instability (VISI) and ulnar carpal translocation. Accompanying carpal instability was more often seen in elderly patients. To a certain extent, the patterns of instability were related to the type of fracture and palmar tilt angle (PTA) values. DISI was often seen in fractures with PTA smaller than -15 degrees, while scapholunate dissociation was seen in fractures with PTA between -5 degrees and -20 degrees. The possible pathomechanics of the accompanying carpal instability were deduced based on the kinematics and influencing factors indicated in this study.