A biomechanical evaluation of the relative load change in the joints of the wrist with ulnar shortening: a 'handbag' model.

The wrist joint is loaded not only while applying a proximally directed load but also, less obviously, while carrying a handbag. Ulnar shortening reduces pressure and relieves pain in the ulnocarpal joint. The present study evaluated the pressure distribution in the wrist joints with ulnar shortening and lengthening when applying traction to the flexed fingers while the fingers were loaded and unloaded. The compressive forces in the loaded wrist were distributed with 67% across the radiocarpal joint and 33% across the ulnocarpal joint. Shortening the ulna by 3 mm increased load in the radius to 80%. Lengthening of the ulna by 1 mm increased its load to 55%. The load share of the distal radioulnar joint was constant even when the ulna was shortened 3-4 mm. It seems advisable to shorten the ulna by 3 mm, since the increased load in the related joints are constant within a range of -2 to -4 mm.