[Load transmission through the wrist joint: a biomechanical study comparing the normal and pathological wrist]

This study was undertaken to elucidate the correlation, if any, between pressure loading and the progress of degenerative osteoarthritis in the human wrist. Nine fresh amputated forearms were used to produce i) a pathological model of a malunion after a distal radius fracture, ii) a model of a triangular fibrocartilage (TFC) tear, and iii) a model of a scapholunate dissociated wrist (involving three specimens for each model). On pressure loading, changes in the radioulno-carpal joint and in the midcarpal joint were measured using a pressure sensor. In the malunion of the distal radial end, we found that a pressure fluctuation occurred at more than a 20 degrees dorsal tilt with greater than ulnar +2 mm variance. The loads on the TFC surface and on the scaphoid surface increased, causing the pressure loading site to move dorsally. In the model of a partial TFC resection, sufficient decompression was achieved at the resection site for ulnar 0 mm variance. However, at +2.5 mm variance, the pressure loading caused a concentrated pressure to occur on the TFC surface and the decompression became ineffective. So for a +2.5 mm variance in this model, shortening the ulnar diaphysis is suggested as adequate for a clinical reduction in pressure. In the scapholunate dissociated model, we observed decreased pressure in the radioscaphoid articulation and scaphocapitate articulation, during volar rotation of the scaphoid, while there was increased pressure in the radiolunate and in the lunocapitate articulation. In all models, the focus of the increased pressure was correlated with radiographic findings as being the same as the site of morphological degeneration, suggesting a close correlation between abnormal pressure and the progression of degenerative osteoarthritis.