Malunited Colles' fracture. Analysis of stress distribution.

To try to explain disability in the wrist after malunited Colles' fractures, an experiment was designed to evaluate pressure distribution through the wrist joint with varying degrees of angulation of the distal radius. The results of computer simulation analysis of stress concentration using finite element methods were compared with those of pressure distribution studies on the radial articular surface of cadaveric radii in various positions using pressure-sensitive film. Stress existed in volar regions of the radio-lunate joint under normal pressure in the neutral position, but shifted to dorsal regions of the joint, and was concentrated when dorsal angulation reached 30 degrees. We believe that concentrated loads result in pain and may lead to early degenerative joint disease. Early additional reduction of a displaced fragment or a post-fusion osteotomy should be considered when dorsal angulation exceeds 30 degrees in malunited distal radial fractures to decrease abnormal loading across the wrist joint.