Knee joint implants work as a system and consist of femoral, tibial and patellar components. The tibial component of the prosthesis covers the top end of the shinbone, (tibia); as it comes into the knee. In a rotating platform knee, the tibia is covered with a metal tray. The tibial component is topped with a disk-shaped polyethylene insert. The polyethylene insert sits on a highly polished surface and rotates around a conical post.

The insert lies at the point where the femoral and tibial components meet. This subjects the polyethylene to forces generated by the bending and rotation of the

knee during activity. Even though the physical and mechanical properties of polyethylene are well suited to this job, wear of the insert can happen.

The rotating platform implants are designed to reduce the stresses in the knee which can lead to polyethylene wear and may increase the longevity of the implant.

The Differences
The difference between a rotating platform knee implant and the more traditional fixed bearing implant is mainly in the design of the tibial component. In a fixed knee prosthesis the tibial component is topped with a flat metal piece that securely holds the polyethylene insert. When the knee is in motion, the femoral component glides across the polyethylene. Since the natural shape of the end of the femur, the condyle, is not perfectly rounded, differing amounts of stress are put on the insert at different points in the movement of the knee. In the rotating platform knee prosthesis, the polyethylene insert can rotate slightly, which gives the knee implant a more natural interface between the surface of the femoral component and the polyethylene. Since the polyethylene can rotate with the femoral component, the contact between the two components can be made more even, which can lessen the stress and wear the implant may experience.