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|Knee Replacement Components
A total knee replacement surgery replaces your diseased knee joint with a synthetic implant and eliminates the damaged weight-bearing surfaces that are causing pain. A partial knee replacement involves an implant in just one compartment of the knee, retaining any undamaged parts. While there are non-surgical and surgical interventions short of knee replacement which will often provide temporary relief, the long-term resolution to most knee degeneration will be joint replacement.
There are several different implant designs (total | partial) but each will offer renewed stability and movement. Overall, there are two main benefits to be gained from knee replacement surgery: (1) elimination of pain and (2) improved range of motion. Of all possible surgical interventions, total knee replacement offers the greatest quality of life improvement. The procedure has a high rate of success.
Knee Replacement Components
The knee is located at the juncture of three bones, the femur, the tibia and the patella. The femur (the upper leg bone) and the tibia (the shinbone) are connected by the anterior and posterior cruciate ligaments. The joint is cushioned by the meniscus, a tough cartilage material, during movement. The patella (or kneecap) is a small bone, encased in tendons, that glides up and down in the groove on the top of the femur when the knee is flexed and extended.
Degeneration of the joint can occur as a result of trauma or from wear and tear over time. Whatever the cause of the degeneration, it ultimately means that the patient’s knee will wear down to the point that it causes substantial pain and limits meaningful motion.
The lower part of the replacement knee joint is comprised of a flat metal plate and stem that your surgeon will implant in the tibial bone. This tibial tray can be either cobalt chrome alloy or titanium alloy. It can be fixed by either cement or bone “ingrowth”.
Next, a polyethylene insert is clipped into the tibial tray to serve as the new knee bearing surface. The upper part of the replacement knee joint consists of a contoured metal implant that fits around the lower end of the thigh bone (femur). The inner surface can be fixed to the cut bone surfaces by the surgeon’s choice of bone in-growth or bone cement. The outer surface of the contoured metal shield is shaped to allow the knee cap (patella) to slide up and down in its groove.
The surgeon may choose to retain the natural knee cap or re-surface it. In this case a polyethylene button will be cemented in place.
A diagnosis of advanced osteoarthritis of the knee will indicate the need for total replacement of the knee joint. There are several design options the surgeon might choose from that will help you return to an active enjoyable life.
- Fixed bearing
- Mobile bearing
- Posterior Cruciate Ligament Retaining or Substituting
Special Need Knee Implants: On occasion, patients will require a specialized implant due to their smaller-than-average size or just due to anatomical variances. Special need knee implants include:
- Narrow Femur vs. Normal Femur
- Custom Fit Through Graduated Sizing
Knee Implant Fixation: Knee replacements may be “cemented” or “cementless” depending on the type of fixation used to hold the implant in place. The majority of knee replacements are generally cemented into place. Cemented knee replacements have been used successfully in all patient groups for whom total knee replacement is appropriate for many years, including young and active patients with advanced degenerative joint disease.
In the 1980′s, implant designs were introduced that were intended to attach directly to the bone without the use of cement. Cementless designs rely on bone growth into the surface of the implant for fixation. Most implant surfaces are textured or coated so that the new bone actually grows into the surface of the implant. Screws or pegs may also be used to stabilize the implant until bone ingrowth occurs. Because they depend on new bone growth for stability, cementless implants may require a longer healing time than cemented replacements. More about total knee implants >>
Partial Knee Resurfacing is an innovative procedure designed to provide quicker recovery and improved surgical outcome for patients with osteoarthritis in only one part of the knee. By selectively targeting the portion of the knee that has become damaged by osteoarthritis, surgeons can isolate and resurface only the arthritic portion of the knee without compromising the healthy bone and tissue surrounding it.
Sometimes this procedure is undertaken by using a surgeon-interactive robotic arm system, which allows the surgeon to pre-operatively determine the damaged area of the bone to be removed and to plan the precise alignment and placement of the resurfacing implant specific to the patient’s anatomy. But this is by no means routine and most partial replacements are still done without robotics.
Partial Knee Implants
In situations where only one compartment of the knee is affected, usually the medial compartment, the surgeon might suggest resurfacing or partially replacing damaged knee components. Preserving healthy bone stock is especially important to younger and more active individuals.
- Uni-compartmental or Partial Knee Replacement
- Uni-compartmental Inlay Knee Replacement
- Uni-compartmental Onlay Knee Replacement
- Knee Interpositional Device
- Bi-Compartmental Partial Knee Replacement
Increasingly, orthopedic surgeons are looking to computer-assisted robotic surgical techniques to enhance the knee replacement process – the theory being that computers can enhance the precision and accuracy of hip and knee replacement surgeries. Through computer-assisted surgery, it is possible for your surgeon to obtain a 3-D visualization of the joint which can make it possible to achieve a better alignment of the implant joint.
Minimally Invasive Surgery is when very small incisions are made to carry out the surgery. In hips, MIS is keyhole surgery but in knees what most surgeons actually practice is minimal incision surgery. This simply means that they use a shorter incision. Incisions merely have to be big enough the get the cutting guides and the implants in. More about robotics, CAS, and MIS >> | Computer-Assisted Knee Replacement Surgery >>
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