Mobile Bearing Knee

Mobile Bearing Knee

A particular type of knee implant you may hear about is known as the "Rotating Platform" or "Mobile Bearing" knee. In this version the tibial insert (see the Implant post) is designed to move in between the Femoral component and the tibial component. The femoral and tibial components are fixed to the thigh and shin bones respectively. This allows the insert to remain well mated against the femoral component while still allowing the necessary rotational movement of the tibia (shin) relative to the femur (thigh). The possible benefits are:

• Increased wear resistance since the femur and tibial insert can be made to "match" more closely. Increasing the contact between the components reduces the pressure on the insert making it potentially last longer. In fixed bearing knees, the rotational movement of the femur relative to the tibia has to occur on top of the insert, so it can't be made to match as closely.
• The potential for more natural motion since it allows a greater degree of rotation about the knee compared to fixed designs.

Keep in mind though that since the insert can move it can also dislocate. In addition, the high conformity between the insert and femur of this implant can sometimes limit flexion of the knee compared to other designs. Basically,
increased rotation at the knee (like during a golf swing) can come at the expense of increased flexion.

Note that traditional fixed bearing knees also allow rotation to occur, but in a different way. Rotation occurs on the plastic bearing surface between the femoral component and the tibial insert.

Several studies have shown that the long-term results of both implants are comparable.

The study below found similar results in patients who received one of each type of replacement (one in each leg of course!)

Chiu KY, Ng TP, Tang WM, Lam P. "Bilateral total knee
arthroplasty: One mobile-bearing and one fixed-bearing"J
Orthop Surg (Hong Kong). 2001 Jun;9(1):45-50

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