Force transmission through the distal ulna: effect of ulnar variance, lunate fossa angulation, and radial and palmar tilt of the distal radius.

The relationship between the amount of force transmitted through the distal ulna and seven radiologically apparent anatomic parameters (ulnar variance, radial tilt, palmar tilt, lunate fossa angulation, carpal height, carpal ulnar distance, and ulnar head inclination) was examined in 58 fresh cadaver forearms. A positive, although very weak, relationship was found between the amount of force and the ulnar variance (r = 0.44). This suggests that a clinically more positive ulnar variant wrist will not necessarily cause more force to be transmitted to the head of the ulna than a wrist with a more negative ulnar variance, primarily because the triangular fibro-cartilage complex is thicker in arms with a more negative ulnar variance. Changes in ulnar variance of a forearm due to ulnar lengthening or radial shortening do, however, dramatically alter the force transmission. No other relationships were found between the ulnar force and the other radiologic parameters.