The invention reduces friction and wear in partial hip prosthesis by combining optimized geometry of the articulation and surface treatment of the prosthetic component. The acetabulum is reamed to the bone. One of the articulating surfaces—either that of the reamed acetabulum, or that of the femoral head prosthesis is a-spherical so that a fluid-filled gap is formed at the area of major load transfer. The fluid-filled gap is sealed by an annular area of contact, over which the concave and the convex components are congruent. The preferred surface treatment is by diamond-like coating, which results in very low coefficient of friction and high abrasion resistance against the bone. The prosthetic head is fixed to the femur by either a conventional stem, a perforated shell, or a femoral neck prosthesis screwed onto the femur so that it is partially covered by bone and partially exposed on the medial-inferior aspect, where it abuts the reamed cortex of the calcar region.
