There are two methods of securing the prosthesis to the bones. One relies on an in-growth of the patient's bone to anchor the device, and the other uses "cement". The cement is plastic polymer that serves as an adhesive. The method of fixation utilized is usually based on the patient's age and the quality and condition of the patient's bone. The design of the prosthesis also influences the method of attachment to the bone.
Total knee function
Replacement joints come in many different sizes, and are precision engineered to feel and move as much like a real joint as possible. Most people with an artificial knee joint are not aware of a difference between the feel of the implant and their original knee. The knee replacement allows for less bending than a normal knee. In the knee suitable for replacement, however, the range of motion is often improved postoperatively.
Design changes continue in existing prostheses in an effort to yield better function and longevity. A well implanted prosthesis, in a compliant patient, usually lasts for many years. Since many prostheses now used are improved designs, we can only guess at their longevity. Trauma, wear or loosening may make it necessary to replace a prosthesis. Revision replacements may have a shorter life expectancy than primary implants. Every effort must be made to prolong the life of the total knee which is implanted first. A maximum working life of 10-15 years is reasonable, and more is possible. The physical activity level and patient age are strongly related to the longevity of knee replacements.
The main object of a total knee replacement is relief of pain. Other goals include the correction of deformity and restoration of stability. Prosthetic design constraints limit the range of motion to approximately 0-120. It should be emphasized that total knee replacements are not done to allow patients to return to unlimited activities. Fitness may be maintained by swimming, bicycling, and walking. Golfing and even skiing in some individuals may be considered, but impact loading such as running or jumping should be minimized.
Candidates for total knee replacement