Kinematics of ulnar head arthroplasty.

This in vitro study evaluated the performance of an ulnar head replacement. A joint simulator was employed that produced active forearm rotation in cadaveric specimens, with motion measured using an electromagnetic tracking system. The kinematics of the intact forearm were compared with a partial ulnar head replacement and a full replacement (with and without soft-tissue reconstruction) and a full excision of the ulnar head. There were no differences between intact kinematics and those following prosthetic reconstruction. However, ulnar head excision produced distal radioulnar joint instability in the form of radioulnar convergence and increased anteroposterior translations.