Mobile-Bearing Rotational Platform Knee Implants
What are Mobile-Bearing Rotational Platform Knee Implants?
Mobile-bearing rotational platform knee implants are implants specially designed to reduce wear and improve long-term performance. They are recommended for individuals with an active lifestyle and those who are overweight.
What are Knee Implants?
The knee joint is formed by the articulation of the lower end of the thighbone (femur), the upper end of the shinbone (tibia) and the kneecap (patella). Knee implants are artificial implants that are used to replace the damaged or worn-out bony articular surfaces of the knee usually seen in arthritis.
Knee implants are of different types and have components usually made of metal, ceramic, and hard plastic (polyethylene). The components of knee implants include:
Femoral implant: This component replaces the lower end of the femur. It is curved around the lower end of the femur and has a central groove to allow the gliding movement of the patella.
Tibial component: This component replaces the top of the tibia. It usually consists of a flat metal platform on top of which is a plastic (polyethylene) cushion liner that acts as a shock absorber. An artificial stem may extend from the metal platform into the tibia to provide additional stability.
Patellar component: The surface at the back of the patella may be replaced with polyethylene for smooth gliding movement.
How is the Mobile-Bearing Rotational Platform Component Designed?
The knee is considered a hinge joint, but its motion is more complex as the bones roll and glide against each other as the knee bends. Modern implants are designed to accommodate these complex knee movements.
The tibial component of the knee implant may be designed in two ways:
Fixed bearing: Where the polyethylene portion is firmly fixed to the metal base. When the knee is subject to excessive stress, the components may wear and become loose and painful.
Mobile bearing: In this type, the polyethylene liner is not firmly fixed to the metal base but can rotate a few degrees on either side. This rotational platform design accommodates more natural knee movements and reduces wear of the components from excess activity or weight. The idea is that the force applied to the knee is translated into movement minimizing stress and wear at the bone-cement-implant interface. This should extend the life of the implant while allowing you to participate in activities such as racquet sports. Though long-term studies are still needed to prove the efficacy of this design, the results so far are very encouraging.
Mobile bearing implants cost more and need good support from the knee ligaments to prevent dislocation.
Your doctor will decide what kind of implant you need based on various factors including the condition of your knee, your activity level, age, general health, and the cost and performance of the implant.