Fixed bearing Prosthesis
Femoral component is made of titanium or cobalt chrome alloy.
Tibial component has a high-density polyethylene piece fixed on top of a metal alloy tray that sits on top of the cut tibial surface.
A high-density polyethylene piece replaces the underside of the kneecap in the center of the knee. Some surgeons leave the patellar surface untouched and this gives the same results to the patients.
Disadvantage: Excessive activity and extra weight can accelerate the process of wear to parts of a fixed-bearing prosthesis, causing it to loosen from the bone and become painful. This prosthesis allows maximum flexion of 110 degree at the knee joint.
High Flex knee prosthesis
This prosthesis accommodates greater flexion or more than 125 degree at the knee joint. Flexion of up to 155 degree can be done. For maximum results patients have to undergo intensive physiotherapy.
Advantage: Patients can sit cross legged on the floor, climb stairs with ease as also kneel down on the floor for prayers.
Disadvantage: High flexion will not be achieved in patients whose mobility is very severly restricted before the surgery
Like fixed-bearing replacements, mobile-bearing knees use three components to provide a relatively natural and even interface. The difference between them is in the bearing surface. In a mobile-bearing knee, the femoral component and tibial tray move across a polyethylene insert to create a dual-surface articulation. This helps reduce the amount of wear to the bearing and helps prevent loosening in places where the prosthesis attaches to bone. Mobile-bearing knees are also designed to allow greater rotation of the knee.
Advantage: The polyethylene bearing plate has a large contact area with the femoral component during the whole range of knee joint movement. Hence the stresses on the polyethylene bearing plate are substantially lower than the stresses on the polyethylene plate in the stabile bearing total knee prosthesis. The risk for loosening of the total knee components is low too Disadvantages. Mobile-bearing knee implants are less stable than fixed bearing. They may increase the chance of dislocation and also cost more. The most frequent cause of failure in these prostheses is the accelerated wear, destruction, or dislocation of the mobile polyethylene plate in knees with ligament and soft tissues instability.
Gender Specific Knee
Zimmer has brought forth this knee which is specifically designed for women. It is different in that it has a thinner profile and better contour to fit naturally in the female knee.
This prosthesis is made of a oxidised Zirconium, a ceramic coated metal. Advantages of this implant are.
- Oxinium knee implants offer significantly less wear as their surfaces are harder compared to cobalt chrome implants, so they are expected to last considerably longer.
- An Oxinium knee is more durable and better able to tolerate high activity level and last longer (20 to 25 years) than the traditional cobalt chrome knee (10 to 15 years).
- It is the choice of implant for patients who need knee replacement surgery but are allergic to metals because it does not have nickle.
Requirement for each patient is different. The choice of knee implant for each individual depends on the age and weight of the patient, activity level of the patient. This can be discussed with your surgeon prior to surgery.