[Biomechanical analysis of the deep radioulnar ligaments stabilizing the distal radioulnar joint].

OBJECTIVE: To evaluate the role of the deep radioulnar ligament in the stability of the distal radioulnar joint (DRUJ).

METHODS: In the study, 14 fresh cadaver upper extremities were randomly divided into two groups. After exposuring the palmar and dorsal deep distal radioulnar ligament, one group was marked as palmar deep radioulnar ligament, and the other group was marked as dorsal deep radioulnar ligament. The pronator teres and the supinator were exposed. A Kirschner wire perpendicular to the bone on Lister tubercle of radius was inserted, then another Kirschner wire on the same level of ulnar inserted when the forearm was in neural position, which was kept parallel to the first Kirschner wire. These specimens were mounted on a specially designed jig which held the limb rigidly, keeping the elbow flexion and the ulnar fixation. The radius could freely rotate around the ulnar. Then 50 N force on the pronator teres was applied to simulate the active pronation, and 60 N force on the supinator to simulate the active supination. The active pronation was stimulated, and the displacement of the distal radius was measured with respect to the ulna. The active supination was atimulated, and the displacement of the distal radius was measured with respect to the ulna. The palmar deep radioulnar ligament in one group was cut, then the displacement of the distal radius measured with respect to the ulna when the forearm was in pronation and supination. The dorsal deep radioulnar ligament in the other group was cut, and the displacement of the distal radius measured with respect to the ulna when the forearm was in pronation and supination.

RESULTS: After resection of the palmar deep radioulnar ligament, the displacement of the distal radius with respect to the ulna was statistically significantly different when the forearm was in pronation (t=5.591, P=0.001), but there was no difference when the forearm was in supination (t=0.433, P=0.680). After resection of the dorsal deep radioulnar ligament, the displacement of the distal radius with respect to the ulna was not different when the forearm was in pronation (t=1.000, P=0.356), but there was statistically significant difference when the forearm was in supination (t=6.225, P=0.001).

CONCLUSION: DRUJ is unstable when the forearm is in pronation after resection of the palmar deep ra-dioulnar ligament, and DRUJ is unstable when the forearm is in supination after resection of the dorsal deep radioulnar ligament.