Constrained acetabular liner

A total hip replacement comprising:

• a femoral portion comprising,
• a femoral stem adapted to be implanted into a prepared femur bone of an organism;
• a femoral ball;
• and
• a femoral neck, the femoral neck adapted to connect the femoral ball with the femoral stem,
• wherein the femoral ball comprises a spherical ball surface with a ball radius, a ball center at a geometric center of the spherical ball surface, and a planar surface, wherein the femoral neck is adapted to connect with the ball perpendicular to the planar surface, and wherein the planar surface is located an offset distance from the ball center point less than the ball radius, and wherein the offset distance and the ball radius define a ball height equal to the sum of the ball radius and the offset distance;
• and
• an acetabular cup liner with an inner surface, the inner surface comprising:
• a hemispherical surface having a cup radius of curvature, being disposed about a cup central axis, and intersecting a hemispherical plane perpendicular to the cup central axis, the intersection of the hemispherical surface and the hemispherical plane defining a circle having a circle radius equal to the cup radius of curvature;
• a retaining region continuous with the hemispherical surface, having the same cup radius of curvature, extending along a first arc of the circle on the hemispherical plane, and extending a first distance out of the hemispherical plane;
• and
• an insertion region continuous with the hemispherical surface connected with the hemispherical surface along a second arc of the circle on the hemispherical plane and comprising an increased radius portion, wherein the hemispherical surface does not extend past hemispherical plane in insertion region, wherein a radial distance from the cup central axis to the insertion region is greater than the circle radius,
• wherein a cup opening distance is defined by a maximum opening distance between an edge of the retaining region and an edge of the insertion region, wherein the cup opening distance is substantially the same as the ball height, wherein the cup opening distance is less than twice the ball radius and wherein the ball height and cup opening distance are selected to provide an interference fit between the liner and ball.

An acetabular prosthesis comprising a liner and an anchor, wherein the liner comprises an inner surface and an outer surface, the inner surface comprising:

• a hemispherical surface having a radius of curvature, being disposed about a central axis, and intersecting a hemispherical plane perpendicular to the central axis, the intersection of the hemispherical surface and the plane defining a circle having a circle radius equal to the radius of curvature and wherein the radius of curvature defines a liner center;
• a retaining region continuous with the hemispherical surface, having the radius of curvature, connected with the hemispherical surface at the plane along a first arc of the circle on the plane, and extending a first distance out of the plane;
• an insertion region on the hemispherical plane and connected with the hemispherical surface along a second arc of the circle on the plane and comprising an increased radius portion, wherein the hemispherical surface does not extend past hemispherical plane in insertion region, wherein a radial distance from the central axis to the insertion region is greater than the circle radius, and wherein a maximum opening distance from an edge of the retaining region to an edge of the insertion region is less than twice the circle radius;
• wherein outer surface of the liner is at least partially hemispherical,
• wherein the anchor comprises an anchor inner surface having an anchor center, wherein the anchor inner surface is sized and shape to accept insertion of the liner into the anchor and to closely match the outer surface of the liner.