This operation involves removing a diseased or damaged knee joint, and replacing it with an artificial joint (prosthesis).
This is a major operation, usually done under general anaesthesia, but may be done under spinal or epidural anaesthesia in some patients.
Why is it done?
The normal knee works as a hinge joint, and carries a large percentage of the body weight.
Underlying disorders can worsen the normal wear and tear, and cause damage to the knee joints, such as:
- Morbid obesity - a body mass index of more than 35kg/m²,
- Inflammatory arthritis such as rheumatoid or psoriatic arthritis, and
- Previous trauma leading to secondary arthritis.
Damage to the knee joint causes pain with movement. This is usually treated conservatively, with pain-killers, rest and anti-inflammatories. However, over a long period, accumulated damage to the knee may cause such severe pain and disability, that surgery becomes the only option left.
Patients considered for total knee replacement must be fully investigated for any underlying conditions which may put them at risk during surgery, such as:
- Heart disease,
- Lung disease,
- Infection - especially infection in the joint,
- Peripheral vascular disease,
- Peripheral neuropathy, or
- Clotting disorders.
Any such conditions must first be fully investigated and treated. Total knee replacement is an entirely elective procedure, and there is no excuse for exposing a patient to unnecessary risks by failing to prepare him adequately for the surgery. Blood loss during surgery can be substantial, and the patient may need a transfusion.
How is it done?
A variety of prostheses are available, with slight differences in design. Materials used include metal and high-density synthetic compounds, designed for weight-bearing and durability.
Knee replacement is usually done under general anaesthesia. Prophylactic antibiotics are given at the start of the operation. Treatment is also begun to prevent blood clots forming, to avoid the risk of subsequent pulmonary embolism or stroke. An incision is made over the front of the knee. To gain access to the knee joint, tissues are held out of the way, rather than being cut through where-ever possible.
Diseased and damaged parts of the joint and bones (femur and tibia) are cut off, and the cut surfaces are then shaped to match the shape of the selected prosthesis. The prosthesis is inserted, and must be held in place: this is usually achieved by using bone cement. X-rays can be done in the operating room to verify correct placing and seating of the prosthesis. The overlying tissues are then replaced, and the wound closed.
The patient is kept in hospital for a few days, with good pain management, and continued anticoagulation drugs. Early movement of toes and feet is encouraged. Physiotherapy is started in hospital, and continued after discharge. A programme is followed to encourage gradual exercise and return to walking, using a cane at first, then later, unaided. Normal everyday activities can usually be resumed six weeks after surgery, but high-impact sports are discouraged.
These are seldom found if the surgery is done by experienced orthopaedic surgeons, at established centres. Some potential complications are:
- Anaesthetic and bleeding problems during the operation;
- Thromboembolism - unlikely with adequate pre-operative preparation and post-operative treatment (anti-coagulation) and early mobilisation. Chest pain, sudden shortness of breath and coughing up blood are danger signs;
- Infection - fevers, chills, increased pain over the joint, redness and swelling should alert the patient and doctor. This is a potentially serious problem: if the infection cannot be controlled with high-dose antibiotics, the whole prosthesis may need to be removed, and replaced later when the infection has cleared; and
- Damage to blood vessels or nerves near the joint. - numbness or loss of sensation is common, but paralysis is rare.
In experienced hands, total knee replacement is highly successful, providing pain relief and a return to normal activities for thousands of patients each year. Most prostheses last at least 10 years, some longer in less active and non-obese patients. Many operations can be repeated if necessary, further extending the quality of life for these patients.
(Dr AG Hall)