Role of the extensor carpi ulnaris in the stabilization of the lunotriquetral joint. An experimental study.

Study Design: Experimental laboratory-based research in biomechanics.

Introduction: The mechanisms by which some lunotriquetral (LTq) ligament disruptions remain stable are not known.

Purpose Of The Study: To investigate the contribution of muscles in preventing carpal destabilization when the LTq ligaments are torn.

Methods: Ten fresh cadaver wrists, set vertical in a jig, were isometrically loaded through five wrist motor tendons. Changes in carpal alignment secondary to the application of loads were monitored by a Fastrak™ electromagnetic motion tracking device, before and after sectioning the LTq ligaments.

Results: After LTq ligaments sectioning, wrist loading forced the triquetrum into flexion (5.4° average) and supination (2.9 ). The only muscle capable of extending and pronating the collapsed triquetrum was the extensor carpi ulnaris (ECU).

Conclusions: Inadequate ECU muscle function is an important destabilizing factor in LTq deficient wrists. Dynamic LTq instabilities may benefit from proprioceptionally training the ECU muscle, while avoiding carpal supination torques.