Forearm force transmission after surgical treatment of distal radioulnar joint disorders.

To evaluate the effect of silicone replacement of the distal ulnar, hemiresection arthroplasty and the Darrach procedure on ulnar support of the carpus, changes in force transmission to the radius and ulnar were measured using load cells in axially loaded cadaver arms. Testing of the intact specimens in neutral position showed that an average of 17% of the axial load was borne by the ulna whereas the load decreased to 3.6% after silicone arthroplasty, to 2.4% after hemiresection arthroplasty, and to 1.0% after the Darrach procedure. Only by placing the silicone cap on the ulna to lengthen it by 4 mm did the ulna load become within 75% of that in the intact specimen. In the intact specimen, ulna loading increased with wrist extension and ulna deviation and decreased with flexion and radial deviation, while after the surgical procedures there was no significant change in ulna loading with wrist position.