Knee pain and stiffness can be caused by factors such as wear and tear or injury which cause the progressive degeneration of cartilage (osteoarthritis) reducing its ability to serve as a cushion. The bone ends are allowed to rub together and become roughened and irregular. This causes pain and limits movement. Rheumatoid arthritis (inflammatory arthritis) can cause the joint to become inflamed and swollen as well as damaging the cartilage. Other problems with the knee, including poor alignment of the leg bones, can also lead to deterioration of the knee joint.
An orthopaedic surgeon will assess the need for a knee replacement taking into account medical history, physical examination and x-rays of the damaged knee. A knee replacement is a major operation and there are many things to discuss with the surgeon, including the risks and benefits of the surgery.
There are three main components of an artificial knee joint – the femoral component (to replace the end of the femur), the tibial component (to replace the end of the tibia) and the patellar component (to replace the back of the kneecap). In total knee joint replacement surgery, all of these components are used.
Knee joint replacement surgery can be performed under a spinal or general anaesthetic. This will be discussed with the surgeon and anaesthetist prior to surgery and a decision made as to which is most appropriate.
Surgery begins with an incision being made over the front of the knee joint. The surgeon will expose the knee joint, loosen the muscles and ligaments surrounding it, and turn the kneecap out of its place. The worn surfaces within the joint, including the back part of the kneecap, are removed and the ends of the bones are precisely reshaped. The components of the artificial knee joint are then attached to the bone ends using specialised bone cement, and fitted together. The muscles and ligaments are repositioned and, if necessary, the ligaments are readjusted to achieve the best possible knee function.
At the completion of the surgery a drainage tube will be inserted to drain excess fluid from the new joint. The surgeon then closes the layers of tissue and the skin with stitches and a dressing is placed around the knee.
Antibiotics are given during and after the operation to prevent the development of infection in the new joint. A blood transfusion may also be required. This will be discussed by the surgeon prior to surgery.
The success of the surgery depends on following the recovery and movement instructions while in hospital and on carrying out the prescribed exercises when at home.
The time spent in hospital can vary from about three to six days. The healthcare team (surgeon, physiotherapist and nurses) will make an ongoing assessment of recovery and will recommend when going home is appropriate. A part of the healthcare team’s assessment will be to discuss if special equipment needs to be installed to assist at home or if home help needs to be arranged.
Crutches will need to be used for up to six weeks after the operation. By six weeks, the majority of people should be able to return to a range of normal activities, including driving.
Risks of surgery
As with any surgical procedure there are risks involved with total knee joint replacement. As well as general risks of infection and risks associated with anaesthetic; risks specific to this surgery include:
- The legs may not be the same length after the operation
- Nerves may be injured from swelling or pressure resulting in permanent pain, numbness or loss of function
- The knee prosthesis may become loose and require further surgery.
Everybody (2013) Knee Joint Replacements. Everybody. UMBMedica (NZ) Ltd. www.everybody.co.nz