Hip replacement surgery has been around since the early 1960s. Sir John Charnley experimented in the early 1950s, and he used a small (22 mm) stainless steel ball on a stem in 1962 that he inserted into the femur (hip) bone to replace the femoral head (ball). He then inserted a high-density plastic socket to replace the acetabular (socket) side of the hip joint.  Both were secured with a self-curing acrylic polymer known as bone cement.

via Hip Surface Replacement.