Extrinsic wrist ligaments in the pathomechanics of ulnar translation instability.

A description of the various combinations of ligament disruptions necessary for ulnar translation instability is presented based on a series of cadaver dissections and load studies. Dissections and load studies demonstrated that major ligament disruption, even to the extent that only the dorsal ulnolunate, the palmar ulnolunate or the radioscaphocapitate, and the long radiolunate ligaments were left intact, failed to result in meaningful ulnar translation of the carpus. The radioscaphocapitate ligament alone could not prevent significant ulnar translation. Palmar translation instability was evident with less ligament disruption than that needed for ulnar translation and was always evident if there was ulnar translation. These studies imply that ulnar translation represents a much more global ligament disruption and instability than previously suggested in the literature.