Knee replacement , or knee arthroplasty , is a surgical procedure to replace the weight-bearing surfaces of the knee joint to relieve the pain and disability of osteoarthritis. It may be performed for other knee diseases such as rheumatoid arthritis and psoriatic arthritis. In patients with severe deformity from advanced rheumatoid arthritis, trauma, or long standing osteoarthritis, the surgery may be more complicated and carry higher risk. Osteoporosis does not typically cause knee pain, deformity, or inflammation and is not a reason to perform knee replacement.
Other major causes of debilitating pain include meniscus tears, cartilage defects, and ligament tears. Debilitating pain from osteoarthritis is much more common in the elderly.
Knee replacement surgery can be performed as a partial or a total knee replacement. In general, the surgery consists of replacing the diseased or damaged joint surfaces of the knee with metal and plastic components shaped to allow continued motion of the knee.
The operation involves substantial postoperative pain, and includes vigorous physical rehabilitation. The recovery period is 6 weeks or longer and involves use of a walker and then a cane.
History
Following John 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 favor 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.
Indications
Knee replacement surgery is most commonly performed in people with advanced osteoarthritis. It should be considered when conservative treatments have been exhausted. Physical therapy has been shown to improve function and may delay or prevent the need for knee replacement.
Pre-operative preparation
Knee Arthroplasty is major surgery. Before the surgery is performed, pre-operative tests are done: usually a complete blood count, electrolytes, APTT and PT to measure blood clotting, chest X-rays, ECG, and blood cross-matching for possible transfusion. Accurate X-rays of the affected knee are needed to measure the size of components which will be needed. Medications such as warfarin and aspirin will be stopped 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-anesthetic clinic or may come into hospital one or more days before surgery.
Technique
The surgery involves exposure of the front of the knee, with detachment of part of the quadriceps muscle (vastus medialis) from the patella. The patella is displaced to one side of the joint allowing exposure of the distal end of the femur and the proximal end of the 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 tibial and fibular collateral ligaments are preserved. Metal components are then impacted onto the bone or fixed using polymethylmethacrylate (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 any deformities must be corrected, and the ligaments balanced so that the knee has a good range of movement and is stable. In some cases the articular surface of the patella is also removed and replaced by a polyethylene button cemented to the posterior surface of the patella. In other cases, the patella is replaced unaltered.
Variations
Different implant manufacturers require slightly different instrumentation and technique. No consensus has emerged over which one is the best. 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.
Minimally invasive procedures have been developed in total knee replacement (TKR) to that do not cut the quadriceps femoris muscle. There are different definitions of minimally invasive knee surgery, which may include a shorter incision length, retraction of the patella (kneecap) without eversion (rotating out), and specialized instruments. There are few randomized trials, but studies have found less postoperative pain, shorter hospital stays, and shorter recovery. However, no studies have shown long-term benefits.
Partial knee replacement
Unicompartmental arthroplasty (UKA), also called partial knee replacement, is an option for some patients. The knee is generally divided into three "compartments": medial (the inside part of the knee), lateral (the outside), and patellofemoral (the joint between the kneecap and the thighbone). Most patients with arthritis severe enough to consider knee replacement have significant wear in two or more of the above compartments and are best treated with total knee replacement. A minority of patients (the exact percentage is hotly debated but is probably between 10 and 30 percent) have wear confined primarily to one compartment, usually the medial, and may be candidates for unicompartmental knee replacement. Advantages of UKA compared to TKA include smaller incision, easier post-op rehabilitation, shorter hospital stay, less blood loss, lower risk of infection, stiffness, and blood clots, and easier revision if necessary. While most recent data suggests that UKA in properly selected patients has survival rates comparable to TKA, most surgeons believe that TKA is the more reliable long term procedure. Persons with infectious or inflammatory arthritis (Rheumatoid, Lupus, Psoriatic ), or marked deformity are not candidates for this procedure.
Post-operative rehabilitation
Post-operative hospitalization varies from one day to seven days on average depending on the health status of the patient and the amount of support available outside the hospital setting. Protected weight bearing on crutches or a walker is required until the quadriceps muscle has healed and recovered its strength. Continuous Passive Motion or CPM is commonly used, but its effectiveness is questioned. Patients typically undergo several weeks of physical therapy to restore motion, strength and function. Often range of motion to the limits of the prosthesis is recovered over the first two weeks (the earlier the better). 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 three months and some patients notice a gradual improvement lasting many months longer than that.
Risks and complications
The most serious complication is infection of the joint, which occurs in <1% of patients. Deep vein thrombosis occurs in up to 15% of patients, and is symptomatic in 2-3%. Nerve injuries occur in 1-2% of patients. Persistent pain or stiffness occurs in 8-23% of patients. Prosthesis failure occurs in approximately 2% of patients at 5 years.
Deep Vein thrombosis
According to the American Academy of Orthopedic Surgeons (AAOS), "blood clots in the leg veins are the most common complication of knee replacement surgery. Your orthopedic 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."
Fractures
Periprosthetic fractures are becoming more frequent with the aging patient population and can occur intraoperatively or postoperatively.
Loss of Motion
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 anesthetic 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.
Instability
In some patients, the kneecap is unstable post-surgery and dislocates to the outer side of the knee. This is painful and usually needs
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Island Orthopaedic Group was initiated in 1995 and comprises the following practices: Island Orthopaedic Consultants, Island Spine and Scoliosis, Island Sports Medicine and Surgery