Knee Replacement

What is the Definition of Knee Replacement Surgery?

Knee replacement surgery is undertaken by orthopedic 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.

Knee Replacement Technique

The standard knee replacement technique involves exposure of the front of the knee by a long incision which detaches the quadriceps muscle 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.

Variations of Knee Replacement Surgery

There are many different implant manufacturers and all require slightly different instrumentation and technique for knee replacement surgery. No consensus has emerged over which design of knee replacement 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.

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 increases the post-operative pain and lengthens the 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.

Indications for Knee Replacement Surgery

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

Contra-indications for Knee Replacement Surgery

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.

Pre-operative Work-up

Routine pre-operative work up for major surgery is required. This will often include chest Xrays, ECG, blood tests and blood cross-matching. Accurate X-rays 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-anesthetic clinic or may come into hospital one or more days before surgery.

Post-operative Rehabilitation

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.

Time and Course of Recovery

Post operative hospitalization varies from 1 day following Minimally Invasive Surgery 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 operating involving return to full normal function may take 3 months and some patients notice a gradual improvement lasting many months longer than that.

Prognosis

19/20 patients are very satisfied with the results of total knee replacement with pain relief and improvement in function being the expected outcome.