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.