Hip replacements — the surgical repair of an aged or injured natural hip joint by adding an artificial joint, or implant — date back three centuries. Reasons for these implants are the same now as then: a fracture or similar injury to the hip, arthritis or a wearing down of the joint over time. The goal is to reduce pain and increase mobility.

Although there are varied designs and models of hips built by several manufacturers, there are three basic components of an artificial hip — a stem that is inserted into the femur (thighbone); a ball that attaches to the top of the femur; and a cup that attaches to the pelvis.

Modern implants, increasingly popular since the 1970s, are made from a combination of materials, including plastics, ceramics and metals. Many of the most recent devices were metal-on-metal designs, created with the hope that hip replacements would last longer to give younger, active patients more pain-free mobility for more years.