Endoprosthetic bone joint

Abstract

A prosthetic joint of the type used to replace dysfunctional non-weight bearing joints such as the knuckle, wrist, elbow or shoulder. The preferred embodiment comprises a radial component connected by a concavo-convex socket component to a metacarpal component. The radial component has an intramedullary stem terminating in a cup having a plurality of inwardly extending pins. The concavo-convex socket component is retained in the cup by the articulation of the pins with a plurality of flats which communicate with slots which terminate in apertures. The concavo-convex component includes an opening extending inwardly from one end thereof which defines two communicating bearing surfaces, with the innermost surface being spherical and the outer surface being frusto-conical and having an elliptical cross-section. The metacarpal component includes a ball, a neck area and an intramedullary stem. The ball articulates with the spherical surface of the concavo-convex member component and the neck, which also has an elliptical cross-section, articulates with the frusto-conical surface. The intramedullary stem which is connected to the cup is offset volarly by an amount equal to the offset in the metacarpal component thereby providing a greater moment arm for the weaker tendons of the wrist.