We report an artificial elbow joint with a novel type radial component that we have designed that is now at the stage of trial production.

The humeral component is a trochlea capitulum replacement type with a stem. The ulnar component with a stem has an articular surface distributed not only on the trochlea surface but also on the capitulum surface of the humeral component, and has another concave articular surface toward the radial component. The radial component also has a stem and has a spherical convex articular surface. This surface of the radial component does not assume the conventional anatomical morphology, but the convexity is designed to fit the concave articular surface of the ulnar component. In other words, the new artificial elbow joint is a functionally dissociated type, in which flexion-extension is achieved by the humeroulnar joint while rotation is done via the radioulnar joint. The newly designed artificial joint was used to replace the cadaveric elbow joint. Radiographic studies were conducted to observe the compatibility of each component during extension-flexion and rotationmovements.

By replacing the cadaveric elbow joint with the newly designed artificial elbow joint and performing manual extension-flexion simultaneous with pronation-supination, the flexion positions of the humeral component and ulnar component were not affected, and stable compatibility was obtained for the radial component and ulnar component.

Artificial elbow joints with a radial component have been reported by various authors. However, since the humeroradial joint possesses two movement axes for both flexion-extension and rotation, good compatibility with the humeroulnar joint is necessary. Aradial component that simply adopts the anatomical morphology does no tachieve good humeroradial joint compatibility. The functionally dissociated artificial elbow joint that we have designed is expected to offer a clue to solve these problems.