More and more people are having total knee replacements (TKRs). The demand for new joints is pushing the market. Companies making joint implants are working with doctors to improve product design. Wear is an important feature now that younger and more active patients are getting implants.

TKRs aren't as good as the human knee. Motion is never quite the same. The stress on the new joint is also greater than on the human knee. These two factors typically result in greater wear and tear.

A moveable joint may offer some help. A moveable joint straightens and bends the knee, but it also slides and twists to mimic normal knee rotation. The moveable implant is called a rotating platform TKR. This new implant design might result in less wear and a lower chance of coming loose. Range of motion may be better, with improved motion of the kneecap.

This study looked at knee motion in healthy adults compared to motion in volunteers with knee pain who were waiting for a TKR. The results were compared to three million cycles of simulated motion in mechanized joint implants in a lab. This means that a machine moved the replacement implant through the motion. Three types of implants were tested: the fixed-bearing, rotate only platform, and translate-rotate platform.

The authors conclude that the new moveable implant designs are impressive, but that they aren't really any better than the old fixed style of implant. There did not appear to be any difference in range of motion, function, or complications after surgery.

So far, the newer implants haven't solved the old problems of contact stress and wear and tear on the knee joint replacement. More studies are needed to find a longer lasting implant.

Reference:

Robert B. Bourne, MD, et al. An Analysis of Rotating-Platform Total Knee Replacements. In Clinical Orthopaedics and Related Research. May 2003. Vol. 410. Pp. 173-180.'