[Biomechanics of the normal elbow and following total semi-constrained arthroplasty]

The elbow possesses two degrees of freedom: flexion-extension and pronation-supination. The axis of flexion-extension joins the centers of the capitellum and of the trochlea. The axis of pronation-supination passes through the head of the radius, and through the distal ulnar dome. The functional elbow mobilities include 100 degrees of elbow flexion (30 to 130 degrees) and 100 degrees of forearm rotation (50 degrees of pronation and 50 degrees of supination). The elbow is submitted to high articular contact forces. The joint stability depends on the articular surfaces, capsulo-ligamentous restraints and dynamic muscular contractions. As a practical application of this fundamental knowledge, an experimental study of the effects of total elbow arthroplasty on joint stability and muscle moment arms is reported, insisting on the deleterious effects of implant malpositioning.