In order to understand knee replacement it helps to first understand the knee joint itself, the types of knee replacement surgery, and a little about the knee replacement implants for each type of knee replacement.
The Parts of Your Knee Joint
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.
Total Knee Replacement Surgery
Total knee replacement, also called total knee arthroplasty, is a highly successful surgical procedure which involves replacement of all three compartments of the knee. A total knee replacement replaces the damaged bearing surfaces in your knee that are causing pain.
Total Knee Replacement Implants: 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
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.
Knee Resurfacing and Partial Knee Replacement
Partial Knee Resurfacing and partial (or unicondylar) knee replacement are procedures designed to provide quicker recovery and improved surgical outcome for patients with osteoarthritis in only one or two parts 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
Customized and Personalized Knee Implants
On occasion patients will require a customized knee implant due to their smaller-than-average size or just due to anatomical variances. But increasingly surgeons are opting to create personalized knee implants for patients, which can help correct alignment problems within the knee and improve the likelihood of a successful surgery:
- Personalized Fit Through Graduated Sizing or Customized 3D Modeling
- Narrow Femur vs. Normal Femur
- Gender-Specific Knee Implants for Women
Robotics, Computer Assisted Surgery (CAS), and Minimally Invasive Surgery (MIS)
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 Knee Articles & FAQs