Knee replacement surgery involves removing damaged parts of the knee joint and replacing them with artificial parts. The surgery is performed by separating the muscles and ligaments around the knee to reveal the inside of the joint. The ends of the femur (thigh bone), tibia (shin bone) and patella (underside of the kneecap) are removed. They are replaced by artificial parts. The artificial knee typically consists of a metal stem at the end of the femur, a metal-and-plastic channel on the tibia and a plastic button in the kneecap. Knee replacement surgery is usually done on people suffering from osteoarthritis, physical injury or other destructive diseases.
Risks of knee replacement
Knee replacement surgery is a complex procedure and, therefore, several risks are involved:
(a) The most common complication is blood clots in the veins. If the clots remain in the legs, they do not pose any danger. However, they may dislodge and travel through the heart to the lungs, causing pulmonary embolism – a condition which can be fatal. Symptoms of pulmonary embolism are chest pain and shortness of breath. Blood-thinning drugs are usually prescribed after surgery to prevent clots from forming.
(b) The risk of infection in knee replacement is higher as it is comparatively more invasive than other operations. Patients faces a higher risk if they have rheumatoid arthritis, diabetes, have been taking cortisone, or if the knee replaced has had a previous infection. Infections of the bladder, teeth, prostate, kidneys or any part of the body at the time of surgery also increases the risk of surgical infection.
(c ) Loosening of the artificial parts from the bone is a common long-term complaint. How long the artificial parts will bond together depends on factors such as: How well was the surgery done? How hard are the patient’s bones? How active is the patient after surgery? Obviously, excessive impact on the implant can cause the bond to loosen. Is the patient overweight?
(d) The skin wound may not heal completely, and parts of the skin may die after the operation. In such a case, skin grafting is necessary.
(e) Nerves may be damaged during the surgical procedure. Small skin nerves usually get cut, which results in numbness for a few months. Another common casualty is the peroneal nerve. This is the nerve to the muscles that brings the foot up toward the face. If it happens, the affected nerve needs six to 12 months to recover.
(f) Injury to the arteries of the leg is a rare but serious complication. A patient needs to return to the operating theatre to have the damaged repaired by a vascular surgeon. If not, amputation of the leg is necessary.
(g) For reasons unknown, some patients form excessive post-surgery scar tissue — a condition called arthrofibrosis. As a result, bending of the knee becomes restricted.
(h) Though allergy to plastic has never been reported, a few patients can develop allergy to the metal parts of the implant.
Prior to surgery
The patient’s medical history is reviewed. The joints adjacent to the diseased knee are also evaluated. Replacing a knee joint which is adjacent to a severely damaged joint may not improve movement. Routine blood tests for liver and kidney function are conducted to check for anaemia, infection, or abnormal metabolism. Chest X-ray and an electrocardiogram are also done to detect heart and lung disease that may disqualify the patient from surgery or anesthesia.
A knee replacement procedure requires between two to three hours. After surgery, patients are taken to a recovery room, where vital organs are monitored. They are returned to their hospital room after they are stable. Passage of urine can be difficult for a few days, and this condition can be aggravated by pain killers. Usually, a catheter is inserted into the urethra to allow the flow of urine. Physical therapy can begin 48 hours after surgery, and it is common for patients to suffer some pain and stiffness. A therapist will use knee immobilizers to stabilize the knee while patients are undergoing physical therapy. A continuous passive motion (CPM) machine is later attached to the operated leg. The machine constantly moves the knee through various motions for hours while the patient relaxes.
After patients are discharged, they can start walking using a walker and crutches. It is important for them to continue a therapy programme at home to achieve optimal result of the surgery.