Low wear ball and cup joint prosthesis

An articulating joint prosthesis for use between two normally articulating bones, comprising

• an articulating cup member attachable to one of the bones and comprising a body having a generally hemispheric cavity provided with a spheroidal internal surface including a first hard spheroidal articulating surface formed on a radius R.sub.1,
• an articulating ball member attachable to the other of said bones and having a generally ball-shaped body provided with a spheroidal surface including a second hard spheroidal articulating surface formed on a radius R.sub.3 and slidingly contacting said first articulating surface in an area of intimate contact in which R.sub.1 differs from R.sub.3 by no more than 50 micrometers, said ball and cup having gradually diverging surfaces outside the area of intimate contact formed respectively on radii R.sub.2 and R.sub.4,
• the respective first and second articulating surfaces in the area of intimate contact being configured so that the area of intimate contact ranges from 0.12 .pi.R.sub.3.sup.2 to 1.65 .pi.R.sub.3.sup.2, said respective first and second spheroidal surfaces diverging gradually immediately adjacent said area of intimate contact to provide a non contact area between said spheroidal surfaces characterized by the relationship at a position X
• g=(R.sub.2 -R.sub.4)(1-D.sup.2).sup.1/2 +[R.sub.4.sup.2 -(X*-R.sub.4 D).sup.2 ].sup.1/2 -[R.sub.2.sup.2 -(X*-R.sub.2 D).sup.2 ].sup.1/2,
• where X*=X-R.sub.1 (1-D), D=cos(.phi./2), and R=(R.sub.4 R.sub.2)/(R.sub.4 -R.sub.2), and wherein X is located on an X-Y coordinate system having its origin at the center of the area of intimate contact with the X axis perpendicular to the contacting surfaces of the ball and cup at the center of the area on intimate contact, and where g is the gap between said spheroidal surfaces in the non contact area measured parallel to the Y axis at said position X, wherein R, in meters, ranges from 1 to 14, and wherein the first and second articulating surfaces in the area of intimate contact are each characterized by a centerline average surface roughness of not greater than 0.1 micrometers.