Types of Prosthetic Hip Replacements

When hip replacements were originally developed in the middle of the 20th century, it was assumed that the people who received them wouldn't need them for very long, and the prostheses made were created to last for about a decade. But with people living longer and, in some cases, needing hip replacements earlier in life, new types of hip replacements have been developed that will last longer---at a price.

Identification

• All hip replacements, no matter what type, follow the same basic structure that mimics the structure of the bones in the hip joint. The head of the femur is replaced with a prosthetic ball and stem (the stem is inserted into the remaining femur bone). A cup is fitted into the pelvis. When the operation is done, the ball moves within the cup, recreating the movement of the original hip joint.

Metal/Plastic

• The most common type of prosthetic hip replacement is made out of metal and plastic---metal for the ball and stem, and polyethylene (a type of plastic) for the cup. The advantage of this type of prosthetic hip replacement is that it's comparatively cheap, and that its effects on the body are relatively well-known as it's been in use for so long. However, the plastic cup can wear down over time---about 10 to 15 years. With people living longer and leading more active lives, a metal/plastic hip replacement might actually have to be replaced.

Metal-on-Metal

• Hip replacements can be made entirely out of metal, with both ball and stem and cup made out of cobalt chrome. These types of hip replacements theoretically can last forever---or at least much longer than a human lifetime. However, there is some concern that friction between ball and cup releases metal ions into the body. Metal-on-metal hip replacements are more expensive than traditional metal and plastic models.

Ceramic

• Ceramic hip replacements have no metal at all---instead the ball and stem and the cup are made out of ceramic. Ceramic hip replacements are even less likely to wear down than metal-on-metal hip replacements, but there are worries that the ceramics may break inside the body. Also, you might be able to hear the ceramic replacement squeaking when you move. Ceramic replacements may be a good option for people with metal sensitivities; just like metal-on-metal replacements, they are expensive.

Other Options

• Traditional metal-on-plastic hip replacements have been updated, with stronger cross-linked polyethylene providing a cup less likely to wear down. Hip resurfacing---in which a metal cup is placed over the head of the femur---has become an alternative to total hip joint replacement. Ceramic-on-metal and ceramic-on-plastic hip replacements are being tested and may be an option for future hip replacement surgeries.