Kinematic and torque-related effects of dorsally angulated distal radius fractures and the distal radial ulnar joint

Purpose: The purpose of this study was to examine the torque required to achieve a full range of motion of the distal radioulnar joint (DRUJ) as a result of increasing dorsal angulation from simulated fractures of the distal radius. Based on this study the accepted amount of dorsal angulation of the distal radius can be determined. Methods: In 9 fresh cadaver limbs motion of the DRUJ was simulated by a custom motion and loading device. The malunion model of the distal radius was controlled by a specially designed external fixation frame that provided control in 6degrees of dorsal angulations (N, 0degrees, 10degrees, 20degrees, 30degrees, and 40degrees). The study included an intact and nonintact triangular fibrocartilage complex. Results: This study showed that torque across the DRUJ was affected by the degree of simulated malunion of the distal radius. With more than 30degrees dorsal angulation the torque across the DRUJ was increased in both muscle loading and unloading conditions. Although significance was not noted with resistive loading this study showed torque changes with as little as 10degrees malunion of the distal radius. Conclusions: We conclude that reduction of distal radius fractures to within 10degrees of dorsal angulation is needed to allow patients to maintain full forearm and wrist rotation.