During the years from 1970-2000—and into the first few years of the 2000’s—hip implant prostheses were largely constructed of ceramic, polyethylene, and metal-on-plastic (the longest tried-and-tested bearing). The femoral stems were generally constructed of a cobalt and chrome alloy, while the concave cup liner was made of polyethylene, a type of plastic. The metal-on-plastic components were chosen for durability and performance, and were the least expensive type of bearing. Since all implants shed at least some level of debris as the patient engages in physical activities, the polyethylene particles of a metal-on-plastic component have been found to be a source of infection in some cases.
The rate of wear for a metal-on-plastic hip implant device is still very low—about 0.1 millimeters per year. Ceramic devices have high wear resistance already built in (only 0.0001 millimeters per year) and are a good combination for reliability as well as longevity. One of the few problems noted with ceramic hip implants is the tendency to make “squeaking” noises. In some cases these noises are so disruptive as to lead to a revision surgery.
While metal-on-metal implants were in use as far back as 1955, it was not until 1999 that the metal-on-metal hip implant garnered FDA approval. Some ceramic-on-polyethylene implants incorporate a vitamin E-stabilized bearing material which is expected to improve the longevity of the hip implants; ceramic-on-polyethylene implants have a wear rate about 50% less than metal-on-polyethylene hip implants.
As an alternative to total hip replacement, hip resurfacing has been used in patients younger than 55. Hip resurfacing surgery re-shapes the head of the femur, then resurfaces the head with a metallic shell, inserting a metal socket into the pelvis to support the resurfaced femur joint. Patients with mild-to-moderate pain may find this less-invasive surgical procedure reduces their pain and gives them a higher level of joint stability, however the procedure has not had a high rate of success among women.