Below are brief descriptions of some of the most commonly used hip replacement implants. Not all implants are options for all patients. These are general statements about the different implants; if you have specific questions about a particular implant you must discuss this with your doctor!
- Metal and Plastic Implant
The metal and plastic implants are the most commonly used hip replacement implants. Both the ball and the socket of the hip joint are replaced with a metal prosthesis, and a plastic spacer is placed in between.
The metals used include titanium, stainless steel, and cobalt chrome. The plastic is called polyethylene. The implant is secured to the bone by one of two methods; it is either press-fit or cemented into place. In the press-fit method, the implant is fit snuggly into the bone, and new bone forms around the implant to secure it in position. When an implant is cemented, a special bone cement is used to secure the prosthesis in position.
- Metal-on-Metal Implant
Metal-on-metal implants use similar materials, but there is no plastic piece inserted between. Metal-on-metal implants do not wear out as quickly as the metal and plastic materials. The metal and plastic implants wear at a rate of about 0.1 millimeters each year. Metal-on-metal implants wear at a rate of about 0.01 millimeters each year, about 10 times less than metal and plastic.
Despite the low wear rates, it is not known that metal-on-metal implants will last longer. There are also concerns about the wear debris that is generated from the metal-on-metal implants. Metal ions are released into the blood, and these metal ions can be detected throughout the body. The concentration of these metal ions increases over time. There are no data to show that these metal ions lead to increased rates of cancer or disease, but no one knows for sure.
- Ceramic-on-Ceramic Implant
Ceramic-on-ceramic implants are designed to be the most resistant to wear of all available hip replacement implants. They wear even less than the metal-on-metal implants. Ceramics are more scratch resistant and smoother than any of these other implant materials.
Unfortunately, there are also problems with ceramic implants. Again, there is no long-term data available on how well these implants work over time. Also there are concerns that these ceramic implants can break inside the body.
- Metal and Highly Crosslinked Polyethylene
One of the more commonly used implants are new types of plastic that are designed to be more resistant to wearing out. These so-called highly crosslinked plastics are manufactured in a way that they wear out less quickly than the traditional plastics. These new implants have only been available for a few years, so whether or not they do work better than traditional plastic implants, we will not know for quite some time.