KNEE REPLACEMENT

In a healthy knee, smooth cartilage covers the ends of the femur and the tibia.  The cartilage acts as a cushion between these weight-bearing surfaces and allows the bone ends to glide easily over one another, allowing for painless movement. Muscles and ligaments give side-to-side stability. A synovial membrane lines the joint and produces synovial fluid (a clear lubricating fluid) in order to lubricate the joint.

Knee pain and stiffness can be caused by factors such as wear and tear or injury which cause the progressive degeneration of cartilage leading to arthritis of the knee 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.

The surgery

A knee replacement has smooth surfaces which replace the worn surfaces within the knee joint. The prosthesis is made of metal and hard plastic components that fit together during surgery. 

Knee joint replacement surgery can be performed under a spinal or general anaesthetic. This will be discussed with the anaesthetist prior to surgery and a decision made as to which is most appropriate. 

The procedure usually takes about 2 hours.  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 knee joint replacement 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.

Antibiotics are given during and after the operation to prevent the development of infection in the new joint.

Measures to prevent the formation of blood clots and reduce leg swelling may be prescribed. These may include compression stockings, inflatable leg coverings (compression boots), and blood thinning medication. Foot and ankle movement also is encouraged immediately following surgery to encourage blood flow in the leg muscles, which also helps to prevent leg swelling and blood clots.

Recovery

After surgery, a physiotherapist will work with you to set recovery and movement guidelines. Initially these include gentle knee-bending exercises and walking. Ongoing exercises are designed to increase the range of motion of the new joint and to strengthen the surrounding muscles, particularly the thigh muscle (quadriceps). Strength in the quadriceps will help to keep the knee joint stable, therefore protecting the new joint.

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 is usually about 3 to 4 days. 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 an anaesthetic, risks specific to this surgery include: 

•  Infection

•  Ongoing pain

•  Bleeding

•  Blood clots in the legs or lungs

•   The knee prosthesis may become loose and require further surgery.