There are two main types of hip replacement operation, but a number of different components and surgical techniques may be used.
Total hip replacement
In a total hip replacement, part of the thigh bone (femur) including the ball (head of femur) is removed and a new, smaller artificial ball is fixed into the rest of the thigh bone. The surface of the existing socket in the pelvis (the acetabulum) is roughened to accept a new socket component that will join up (articulate) with the new ball component.
Many artificial joint components are fixed into the bone with acrylic cement. However, it's becoming more common, especially in younger, more active patients, for one part (usually the socket) or both parts to be inserted without cement. If cement isn’t used, the surfaces of the implants are roughened or specially treated to encourage bone to grow onto them. Bone is a living substance and, as long as it’s strong and healthy, it’ll continue to renew itself over time and provide a long-lasting bond. Where only one part is fixed with cement, it’s known as a hybrid hip replacement.
The replacement parts can be plastic (polyethylene), metal or ceramic and are used in different combinations:
- Metal-on-plastic (a metal ball with a plastic socket) is the most widely used combination.
- Ceramic-on-plastic (a ceramic ball with a plastic socket) or ceramic-on-ceramic (where both parts are ceramic) are often used in younger, more active patients.
- Metal-on-metal (a metal ball with a metal socket) is very occasionally used in younger, more active patients.
Metal-on-metal hip resurfacing
Resurfacing the original socket and the ball of the thigh bone is a different form of hip replacement. Instead of removing the head of the thigh bone and replacing it with an artificial ball, a hollow metal cap is fitted over the head of the thigh bone. The socket part of the joint is also resurfaced with a metal component.
People who have this type of operation have a lower risk of dislocation and may be able to return to a higher level of physical activity compared with those having a conventional hip replacement.
This type of hip surgery is linked with a release of metal particles from the joint replacement materials, which may cause local inflammatory reactions and have unknown effects on your general health. The complication rates and early repeat surgery rates for hip resurfacing procedures in the National Joint Registry for England and Wales are much greater than for conventional hip replacements. Complication rates are particularly high in older patients and in women. Metal-on-metal resurfacing isn’t suitable for people with low bone density or osteoporosis, where the bones are weakened.
Little is known about the long-term performance of these joints as the technique hasn’t been in use for as long as total hip replacements. However, the poorer mid-term performance for these types of hip replacement means they're being used less frequently in the UK and in other countries.
Read more about recent guidance on metal-on-metal hip replacements.