Major joint replacement is one of the success stories of the late twentieth century, providing the greatest changes in quality of life measurements of all medical treatments or operations. Total knee replacement has now developed from a less predictable operation to a routine procedure with good long-term results for severely osteoarthritic joints. Populations in developed countries are rapidly getting older and total knee replacement is set to overtake total hip replacement as the most performed joint replacement.

Osteoarthritis is a degenerative joint condition which is more common the older a person becomes, and is the most prevalent joint condition in human populations. The most affected joints vary, with some people having spinal and finger changes whilst other suffer OA of the major joints such as the hips and the knees. Major joint disease is more disabling as it tends to compromise normal mobility and so reduce independence. The patient can suffer from loss of knee movement, reduction of knee power, grating and crunching of the joint and pain, for which weight loss, muscle strengthening, painkilling medication and physiotherapy can be useful. If normal therapies are not successful then knee replacement is the remaining option.

The osteoarthritic joint surfaces are precisely cut away in knee replacement and metal and plastic surfaces are substituted. These are:

Femoral component. This is a steel alloy and replaces the arthritic end of the thigh bone.

The tibial component, again of metal, replaces the flat top of the shin bone.

Plastic insert. This is a high density polyethylene and reduces friction between the two main components.

Patellar button. This is also plastic and replaces the back surfaces of the kneecap. If this is not replaced then persistent anterior knee pain can be a problem.

These components are placed in position using cement which acts more like a grout than an adhesive.

After the surgery the physio needs to address the immediate problems that the operation causes in the patient's knee. Inflammation, knee swelling, muscular weakness and pain interfere with the rehabilitation and the physiotherapist initially targets treatment at these problems. A Cryocuff, a compression and cold therapy device, can be used to apply pressure to the swelling and keep up cold therapy for pain relief, with the patient encouraged to take the analgesia regularly. This improves muscle activation as the physio teaches knee flexion and static quadriceps exercises to be performed every hour, to re-establish knee range of movement and muscular control of the joint.

Next the physiotherapist assesses the patient for suitability for their first mobilisation, checking the operation note, the patient's medical observations and the condition of the legs themselves. The operated knee has to have enough stability to safely weight bear, as an epidural can cause profound loss of muscle power and prevent safe mobilisation until the drugs wear off. The patient is mobilised into standing by the physio with an assistant and encouraged to walk a small distance with elbow crutches or a Zimmer frame for more elderly persons. Operative protocol usually encourages normal weight bearing through the new knee as this helps restore normal patterns of muscular activity and improves circulation.

Outpatient physiotherapy aims to restore normal muscle power and function, joint range of motion and regain functional abilities. Initial exercises include knee hangs for full passive extension (very important for normal knee function), inner range quadriceps to restore active extension to full range and knee flexion to increase range. Resisted flexion over the edge of a bed helps the quadriceps relax by reciprocal inhibition and allows increases in flexion range. This can be manually resisted by a physio or performed against a spring or Theraband. Massage to the scar area is also useful to mobilise the scar and free up the tissues.

Further rehabilitation is more likely to take place in the gym, concentrating on functional activities such as moving from sitting to standing and step ups and strengthening work with Theraband and the gymnastic ball. Work on range of motion will continue using resisted exercises and static bicycling and patients can usefully work on proprioception using the wobble board and other balance related activities. Proprioception is the normal ability of a joint to sense its position in space and this is very important for normal activity and safe walking. Normal gait patterns are encouraged and abnormal patterns corrected.