If your knee pain becomes life limiting and hasn't responded to more conservative treatments, such as lifestyle modification and medication, your doctor may recommend knee replacement. Replacing the knee joint can relieve pain and restore your quality of life.
Knee implants are designed with a combination of metal and plastic, which allows the implant to move more smoothly with minimal wear and tear.
There are three criteria the materials used in implants must meet:
- They can be placed in the body without rejection
- They must duplicate the knee structure that they are replacing
- They must be able to withstand wear and tear over a long period of time
In a total knee replacement, up to three bones can be replaced:
- The femur. The lower part of the thighbone (femur) is covered by a metal component, which has grooves to enable the kneecap to move smoothly.
- The tibia. The tibial part of the replacement is usually a flat platform made of metal, cushioned by durable plastic.
- The patella. A dome-shaped piece of durable plastic is intended to mimic and replace the patella.
Today's knee implants are more complex than the first ones introduced to the market, and there are more to choose from than ever.
Modern knee implants are as complex as the knee joint itself and mimic the natural motion of the knee. Some designs are also capable of preserving your own ligaments.
Knee implants also can be gender specific, thanks to studies that have shown male and female knees have different shapes and proportions.
Your doctor will work with you to find the implant that suits you best. Among the factors that will be considered when choosing an implant include your age, weight, activity level, overall health, as well as your doctor's experience with a particular implant.
There are two basic implant types:
The majority of knee replacement recipients will get a fixed-bearing prosthesis. In this type of joint, the plastic in the tibial component is attached firmly to the metal implant, while the femoral component moves along the surface.
Fixed-bearing prostheses are designed to last a long time with less wear.
Mobile-bearing prostheses are more likely to dislocate, particularly if the surrounding ligaments are weak. They may also cost more than fixed-bearing prostheses.
Cemented vs. Cementless Implants
Knee implants can be secured into place in one of three ways:
- Cemented fixation. To hold the implant in place, many surgeons use a fast-curing bone cement. The cement can last as long as 20 years, though other factors such as weight, lifestyle and overall health can impact the longevity of the implant.
- Cementless fixation. Cementless implants depend on new bone growth to remain stable. Screws and pegs may be used to add stability while the bone growth occurs. Because bone growth takes time, cementless implants require a longer recovery period.
- Hybrid. In a hybrid fixation, the femoral part of the implant is attached without cement, while the patellar and tibial components are cemented.
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