In a modern total knee replacement, all of the artificial parts are cemented to the bone in order to create a solid attachment. This has worked extremely well for over 30 years, but in younger, heavier, and more active patients, the cement bond may loosen over time, much like grout in your bathroom. Based upon our experience with hip replacement implants, uncemented fixation, where the bone bonds to the implant, may be advantageous in the long run. If the body can form a living bond to the implant with your own bone, it is possible that the implant will last longer.
The concept of uncemented fixation of a total knee replacement implant is an attractive one, because in general, bonding the bone to an implant is thought to result in greater longevity of the artificial joint. It is thought that by having the bone directly attach to an implant, there is a biologic interface that can respond to stresses and will not deteriorate over time. In traditional total hip replacement, for example, most surgeons now perform uncemented (cementless) fixation of both the femoral stem and the acetabular component.
Cement to attach an implant to bone has been used for over 50 years in orthopedic surgery. It is theorized to be the "weak link" in an artificial joint replacement because it could degrade over time and perhaps be affected by a patient's activity level. On the other hand, it offers an immediate bond to bone without the need to wait some time to achieve a solid attachment.
Cement has different properties when subjected to different kinds of stress; it is very strong in compression, but weak in tension. Thus, in a total knee replacement, where the components are mostly in compression, biomechanical engineers have wondered whether uncemented components would have any benefit over cemented fixation. A traditional total hip replacement is more subject to tension along the lateral side of the femoral stem, so uncemented fixation does make sense for a traditional total hip implant.
As knee replacements are being performed more in younger patients, it is desirable to achieve the longest lasting bond to the implant as possible. I believe an uncemented total knee replacement implant may potentially last longer in these patients because of this "living bond."
I have been using uncemented total knee replacement implants selectively for over 15 years and been extremely pleased. Although I am not sure it will demonstrate superiority to cemented fixation, I am intrigued by the possibility. So, if uncemented total knee replacement fixation is something you are interested in, please let me know before your surgery.