Pressure distribution in the radiocarpal joint measured with a densitometer designed for pressure-sensitive film.

To measure the pressure distribution in the radiocarpal joint, a biomechanical study was done with fresh cadavers and pressure-sensitive film. With a load of 100 newtons, the contact locations were identified for 27 different wrist positions and the peak articular pressures and contact area were measured. Normal wrists were studied first, then modified to show different ulnar variances, and then to be models of malunited Colles' fractures of increasing severity. The contact locations of the scaphoid and the lunate were separate, and the mean peak articular pressures were 2.8 and 2.7 megapascals, respectively, for the normal wrists. In the radiolunate articulation, this mean increased by 27% with 2.5 mm ulnar minus variance and decreased by 22% with 2.5 mm ulnar plus variance. In the models of malunited Colles' fracture, the contact locations shifted from volar to dorsal, and the contact area decreased as the deformity became worse.