Influence of forearm rotation on proximal radioulnar joint congruency and translational motion using computed tomography and computer-aided design technologies.

Abstract

The contact areas of the articular surfaces in the proximal radioulnar joint (PRUJ) change, depending on the rotational position of the forearm. We investigated the in vivo congruency index of the PRUJ and translational motion of the radial head relative to the lesser sigmoid notch with forearm rotation. Computed tomography scans of 12 healthy adult elbows were obtained in 3 forearm positions: full supination, neutral, and full pronation. The translation of the center of the radial head at the level of the PRUJ was measured using computer techniques, and a computer-aided design (CAD) program was used for analysis of the congruency index. The radius of the radial head and lesser sigmoid notch, as well as the distance between the radial head and lesser sigmoid notch, were used as parameters of the congruency index. The mean translation of the radial head was 1.17 mm. The mean ratio of the radius of the radial head to the lesser sigmoid notch was 0.83:1 in neutral position, 0.77:1 in pronation, and 0.92:1 in supination. In supination, the ratio of the radius was more congruent than in neutral and pronation. The mean ratio of the distance between the radial head and the lesser sigmoid notch was 0.15:1 in neutral position, 0.11:1 in pronation, and 0.10:1 in supination. In neutral position, the distance was significantly greater than those in the pronation and supination. In supination, the PRUJ was the most congruent, and the distance between the radial head and the lesser sigmoid notch was minimal (0.10:1). Our findings confirmed the changes of PRUJ congruency during forearm rotation, and this implies changes of intrinsic osseous stability of the PRUJ during forearm rotation.