Many different types of designs and materials are currently used in artificial hip joints. All of them consist of two basic components: the ball component (made of a highly polished strong metal or ceramic material) and the socket component (a durable cup made of plastic, ceramic or metal, which may have an outer metal shell).
The hip replacement bearing surfaces refers to the surface where the ball meets the socket and this surface has to be very smooth so that hip functions well and lasts for a long time. The bearing surface is a metal head with a special polyethylene known as highly cross-linked polyethylene. This polyethylene has been specially treated so that it is very smooth with very low wear rates, meaning it lasts for a long time if the hip replacement has been put in properly.
Nowadays, besides metal and polyethylene, other pairs of bearing surfaces include the following:
- Metal head on metal cup
- Ceramic head on ceramic cup
- Ceramic head on polyethylene cup
These are known as alternate bearings and have very low wear rates. In recent years, metal on metal bearings have fallen out of favour and several of these products have been recalled from the market and thus, we do not use such products. You can read a technology overview release on metal on metal bearings by the American Academy of Orthopaedic Surgeons.