Knee Replacement

Knee replacement, or arthroplasty of the knee, is a commonly performed operation done to relieve the pain and disability from rheumatoid arthritis or more often osteoarthritis of the knee.

The Knee Replacement can be Total Knee replacement, Unicompartmental Knee replacement or Patellofemoral replacement.

Total Knee arthroplasty involves replacement of all three compartments of the Knee (Medial, Lateral and Patellofemoral compartment).

Unicompartmental Knee arthroplasty involves replacing one or both of the medial and lateral compartments.

Patellofemoral replacment involves replacing the patellofemoral- The joint between undesrurface of the Knee cap (Patella) and the femur.

This operation is undertaken by orthopaedic surgeons and consists of replacing the diseased and painful joint surfaces of the knee with metal and plastic components shaped to allow continued motion of the knee.

The standard technique involves exposure of the front of the knee by a long incision which detaches part of the quadriceps muscle (in fact the vastus medialis) from the kneecap. This is a key factor in the lengthy recovery from the operation. The muscle has to heal. The kneecap is displaced to one side of the joint allowing exposure of the distal end of the thighbone (femur) and the proximal end of the shinbone (tibia). The ends of these bones are then accurately cut to shape using cutting guides oriented to the long axis of the bones. The cartilages and the anterior cruciate ligament are removed; the posterior cruciate ligament may also be removed but the collateral ligaments are preserved. Metal components are then impacted onto the bone or fixed using poly methyl methacrylate (PMMA) cement. A round ended implant is used for the femur, mimicking the natural shape of the bone. On the tibia the component is flat, although it often has a stem which goes down inside the bone for further stability. A flattened or slightly dished high density polyethylene surface is then inserted onto the tibial component so that the weight is transferred metal to plastic not metal to metal. During the operation attention must be paid to correcting any deformities and balancing the ligaments so that the knee moves through a good range of movement and is stable. In some cases the joint surface of the kneecap is also removed and replaced by a polyethylene button cemented to the kneecap. At the end of the surgery the muscle is repaired to the kneecap and the wound is closed. It is common practice to leave a drain in the knee to reduce post-operative swelling from bleeding into the knee. Blood transfusion to replace intra-operative and post-operative losses are commonly required.

There are many different implant manufacturers and all require slightly different instrumentation and technique. No consensus has emerged over which design of knee replacement is the best. The first surgery a patient goes through for a knee replacement is called a primary surgery; any subsequent surgeries (usually to fix or replace the first implant) are called revisions.

Clinical studies are very difficult to perform requiring large numbers of cases followed over many years. The most significant variations are between cemented and uncemented components, between operations which spare or sacrifice the posterior cruciate ligament and between resurfacing the patella or not. Some also study patient satisfaction data associated with pain.

Techniques of Minimally Invasive Surgery are being developed in Total Knee Replacement but have not yet found complete acceptance. The driving force here is to spare the patient the large cut in the quadriceps muscle which could increase post-operative pain or lengthen disability.

Unicompartmental arthroplasty is a different operation with different indications. The joint surfaces of either the inner or the outer sides of the knee are replaced.

Any dental work after this surgery requires an antibiotic before the dental work can be done.

Incapacitating pain from arthritis of the knee affecting everyday activities -- particularly walking -- is the main reason to have a total knee replacement. The patient must be aware of the risks of the surgery and be prepared to take those risks rather than continue with the symptoms.

An open infection in the operative area is generally regarded as an absolute contra-indication to total knee replacement. A source of infection somewhere else on the body is a relative contra-indication. Poor general medical status, mental illness or inability to cooperate with post operative restrictions are relative contra-indications.

Routine pre-operative work up for major surgery is required. This will often include chest Xrays, ECG, blood tests and blood crossmatching. Accurate Xrays of the affected knee is needed to measure the size of components which will be needed. (templating) It is standard practice to discontinue medications such as warfarin some days before surgery to reduce the amount of bleeding. Patients may be admitted on the day of surgery if the pre-op work-up is done in the pre-anaesthetic clinic or may come into hospital one or more days before surgery.

Patients are encouraged to move the operated knee to recover the range of motion early. Protected weight bearing on crutches or a walker is required until the quadriceps muscle has healed and recovered its strength. The use of Continuous Passive Motion is common, but current research has shown it to be ineffective in improving range of motion or decreasing pain levels.

Post operative hospitalization varies from 1 day to an average of 7 days depending on the health status of the patient and the amount of support available outside the hospital setting. Usually full range of motion is recovered over the first two weeks (the earlier the better). Walking with protected weight bearing begins almost immediately after surgery. At 6 weeks patients have usually progressed to full weight bearing with a cane. Complete recovery from the operation involving return to full normal function may take 3 months and some patients notice a gradual improvement lasting many months longer than that. Factors such as quad-sparing surgery, pre-operative function, weight, and recovery regimen may shorten or lengthen recovery time.

According to the American Academy of Orthopaedic Surgeons (AAOS), "blood clots in the leg veins are the most common complication of knee replacement surgery. Your orthopaedic surgeon will outline a prevention program, which may include periodic elevation of your legs, lower leg exercises to increase circulation, support stockings and medication to thin your blood."

Periprosthetic fractures are becoming more frequent with the aging patient population and can occur intraoperatively or postoperatively.

Also according to AAOS, "the complication rate following total knee replacement is low. Serious complications, such as a knee joint infection, occur in less than 2 percent of patients. Major medical complications such as heart attack or stroke occur even less frequently. Chronic illnesses may increase the potential for complications. Although uncommon, when these complications occur, they can prolong or limit your full recovery."

The knee at times may not recover its normal range of motion (0 - 135 degrees usually) after total knee replacement. Much of this is dependent on pre-operative function. Most patients can achieve 0 - 110 degrees, but stiffness of the joint can occur. In some situations, manipulation of the knee under anaesthetic is used to improve post operative stiffness. There are also many implants from manufacturers that are designed to be "high-flex" knees, offering a greater range of motion.

In some patients, the kneecap is unstable post-surgery and dislocates to the outer side of the knee. This is painful and usually needs to be treated by surgery to realign the kneecap. This is very rare, but possible.

In the past, there was a considerable risk of the implant components loosening over time as a result of wear. As medical technology has improved however, this risk has fallen considerably. One implant manufacturer claims to have reduced this risk of wear by 79% in fixed-bearing knees. Another implant manufacturer claims to have reduced the risk of wear by 94% in mobile-bearing, also known as rotating platform, knees. Knee replacement implants can last up to 20 years in many patients; whether or not they actually survive that long depends largely in part upon how active the patient is after surgery.

The minimally invasive approach to surgery is controversial. Proponents believe that the procedure allows the patient to recover quicker. Opponents state that the operation is made more difficult without altering the long term prognosis. They suggest that more technical errors will be made particularly during the "learning curve" when the surgical team is less familiar with the operation. They also say that the procedure is not backed by clinical results.

We still do not know whether cemented or uncemented components last longer in the knee. Most surgeons now cement the tibial component but opinion is divided about the femoral component. Sacrifice of the posterior cruciate is also controversial with some surgeons performing this routinely and others trying to preserve as much normalcy as possible.

Resurfacing the patella is also subject to scrutiny. Some studies have suggested that there is no advantage to resurfacing the patella. However, many surgeons continue to do this because resurfacing the patella at a later operation is also a very big operation.

There are many different designs of total knee replacement. All of them were devised to solve an apparent problem. Studying the outcome from one design versus another is expensive, time consuming and unrewarding because designs change frequently and may be withdrawn by the time a good long term study has been done. Many nations, led by Sweden, have set up registries of joint replacements with voluntary or mandatory reporting of the components and used. These registries may yield information about the outcomes of different designs.

FollowingJohn Charnley's success with hip replacement in the 1960s numerous attempts were made to design knee replacements. Gunston and Marmor were pioneers in North America. Marmor's design allowed for unicompartmental operations but these designs did not always last well. In the 1970s the "Geometric" design found favour as well as John Insall's Condylar Knee design. Hinged knee replacements for salvage date back to Guepar but did not stand up to wear. The history of knee replacement is the story of continued innovation to try to limit the problems of wear, loosening and loss of range of motion.Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts.
Virtual Magic is a human knowledge database blog. Text Based On Information From Wikipedia, Under The GNU Free Documentation License. Copyright (c) 2007 Virtual Magic. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

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