Fixed vs Mobile Bearing Prosthesis

With a "fixed-bearing" prosthesis, the tibial insert is fixed to the metal tibial implant and the femoral component rolls on this cushioned surface. This is the less expensive prosthesis option, however, it has limitations. It allows the patient to bend and stretch the knee, but not to rotate it normally. In some cases, extreme activity and/or weight gain can cause a fixed-bearing prosthesis to wear down more quickly. Worn components can become loose from the bone and this can cause pain. Loosening is the main reason for the new joint failing over time.

With a "mobile bearing" prosthesis, the polyethylene insert can rotate short distances within the metal tibial component. This implant has a rotation that allows a more natural and wider range of knee motion and gives overall better knee function. Over time, as the joint becomes worn, the sliding surface can be replaced more easily than with a fixed-bearing. Mobile bearings, however, are the newer and more modern treatment options, thus they incur higher surgical costs than fixed-bearings. They are not suitable for all patients as they require more support from soft tissue (the ligaments and muscles surrounding the knee) and are more likely to dislocate if these ligaments are not strong. They will not be advised in cases of severe bone deformity.

In order to choose the most suitable type of prosthesis, it is necessary to seek the expert advice of an orthopaedist. The decision should consider factors such as age, mobility and sport, muscular strength and bone quality.