Patent ID: 8574307

Claim:
A joint prosthesis system comprising: a shaft having a lower end and an upper end, the lower end configured to be implanted into a femur, and the upper end having a neck comprising an external cone; a ball having an outer surface and an inner receptacle comprising an internal cone, the internal cone of the receptacle configured to receive the external cone of the neck; an adapter press fit between the external cone of the neck and the internal cone of the receptacle, the adapter having an inner wall facing the external cone of the neck and an outer wall facing the internal cone of the receptacle; wherein the ball has a radial thickness, the thickness extending between the internal cone of the receptacle and the outer surface of the ball; wherein the inner wall of the adapter has a convex bulge opposite a portion of the ball that has the greatest radial thickness; and wherein the bulge areally concentrates force transmission between the shaft and the ball to a load bearing region adjacent the portion of the ball that has the greatest radial thickness, and target concentrates force transmission between the shaft and the ball to a narrow surface region of the neck.