About Total Knee Arthroplasty
Typical total knee replacement implant
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- What is a total knee replacement?
Gerard A. Engh, M.D.
With arthritis, the cartilage covering the ends of the bone within the knee joint is badly worn. Similar to resurfacing a road full of potholes, a total knee replacement artificially replaces the worn and arthritic surfaces of the knee joint. A total knee replacement puts an artificial surface on all parts of the joint that contact each other as the knee bends. First, we remove the damaged cartilage, along with a very small amount of bone, using precise guides and instruments. We then fit a knee implant to the bone. The implant, made of metal and plastic, provides an artificial surface that causes no pain.
What is a partial knee replacement?
A partial knee replacement (usually called a unicompartmental replacement) is done if only part of the knee joint is damaged by arthritis. Think of the knee as having three compartments: an inside, outside, and a front compartment for the kneecap. Most frequently, it is the inside compartment that becomes arthritic. The decision to perform a partial replacement is made only if other compartments have healthy, normal cartilage at surgery.Back to top
The early change that made the most difference was an implant that let the knee rotate and allowed the ligaments to provide stability. Knee replacement surgery was first performed in the 1960's with hinged implants that did not work well. Because the hinged knee did not permit the natural rotation and bending of the knee, the implant loosened shortly after implantation. These early implants also had high infection rates.
In the mid seventies better implants, called condylar total knee implants, were designed. The condylar knee implant allowed for knee rotation. They came in only two sizes and were solid pieces. Initially, orthopaedists were cautious about using the new knee implants because of their experience with hinges, but as good results were recognized, more surgeons performed the operations.
Implant companies then designed implants that were easier to place, as well as better instruments that made the surgery more reproducible. By the nineties, knee replacement surgery was widely accepted as a good operation with excellent pain relief from arthritis.
Early condylar implants came in solid pieces.
Have any recent changes in knee arthroplasty offerred new alternatives to patients? Recently, new techniques and instruments have made it possible to perform a unicondylar knee arthroplasty with a small 2 to 3 inch incision with great precision. This operation, performed at Anderson Orthopaedic Clinic, is based on years of research with unicondylar (partial) knee replacements. Used for patients with arthritis in just one knee compartment, the minimally invasive unicondylar knee replacement reduces recovery time, pain, and risks, such as blood loss and infection.
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Do you anticipate that changes for knee pain and disability will be as great in the next century as in the last one?
I believe that better instruments and new techniques will permit us to put implants in more easily and through small incisions. Patients will recover more quickly. I also see and hope for improvements in materials and designs to reduce wear debris - the culprit that limits the life of today's devices.
I also anticipate that changes in the next century will be aimed at developing medicines and procedures to delay or prevent the development of arthritis. I anticipate that we will develop biologic devices for repairing damaged joints, rather than inserting mechanical devices.Back to top
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