During knee replacement surgery, a prosthetic device must be placed into the knee joint to simulate a real knee. Some of these prosthetics are for the entire knee joint, while others are more suited to partial knee replacements, when only one part of the knee is injured. A variety of factors can influence the choice of knee replacement prosthetic, such as the patient's age, weight, general health and activity level.
Fixed-Bearing and Mobile-Bearing Prostheses
The American Academy of Orthopaedic Surgeons states that most patients receive a fixed-bearing prosthetic. This device uses a plastic called polyethylene that is securely attached to the metal prosthetic underneath. This provides a stable cushion for the femoral part of the prosthetic, which rests on this surface. Lots of activity or extra weight can cause this kind of prosthetic to wear down and become loose, so this is not the best choice for younger or more active patients, states the AAOS. Loosening of the knee prosthetic is a main reason some of these replacements fail. A mobile-bearing prosthetic, although similar to its fixed-bearing counterpart, allows some rotation on either side of the knee. This type of prosthetic depends on more soft tissue and ligaments surrounding the device. If these tissues are not strong, this prosthetic can become dislocated. This type of prosthetic is more suitable to younger and more active patients, according to the AAOS.
Cruciate-Retaining and Posterior-Stabilized Prostheses
The posterior cruciate ligament, located in the back of the knee, allows the knee to roll back when it is bent. Cruciate-retaining knee prosthetics are designed to enable the posterior cruciate ligament to remain and support the knee joint. Keeping this ligament adds support to the knee. Posterior-stabilized knee prosthetics are used when this ligament has been removed. The posterior-stabilized device is shaped to act like the ligament to add support and prevent the femur from sliding too far onto the shinbone when the knee is bent, explains the AAOS.
Unicompartmental Implants
In a total knee replacement, the ends of both the femur and the tibia are resurfaced with implants. If only one side of the knee joint is damaged, small implants are used only on the affected side, called unicompartmental implants. According to Dr. David Fisher, an orthopaedic surgeon, these prosthetics are most effective in individuals who have arthritis that is contained only in one area of the knee. He also states that 90 percent of these types of implants continue to be effective 10 years after being surgically placed.
