Osteoarthritis is a time related joint degenerative condition, the incidence rising rapidly with age, making it the commonest arthritic condition in the world. It develops in various joints in the human body and in some people it particularly affects the large weight-bearing joints of the hip and the knee. As the joint surfaces deteriorate the joint becomes painful, crunches, loses range of motion and becomes difficult to walk on. When conservative measures are not helpful, such as physiotherapy, analgesics, walking aids and weight loss, then knee replacement is considered.

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:

The femoral component, made of metal, which replaces the knuckle-shaped end of the thigh bone.

Tibial component. Again a steel alloy part and replaces the damaged tibial surface.

The joint insert, made of high density plastic, which sits between the tibial and femoral 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.

Cement is used as a grout to fix the components but a precise and tight fit is more important in keeping them in place.

Knee replacement surgery causes weakness of the knee muscles, pain, inflammation and joint swelling, all important problems which the physiotherapist needs to treat promptly. Physios in hospitals often use Cryocuffs to provide cold therapy and compression which reduce the knee effusion and the post-operative pain. Analgesia is encouraged regularly and the physio teaches muscle activation of the quadriceps and knee flexion hourly to get the joint moving. Restoring the muscle control of the knee and gaining joint range of movement is the initial goal of the first few day of therapy.

The physiotherapist then gets the patient up, checking the operative record, reviewing the patient's medical status and assessing the patient and their leg status. Muscular control of the knee must keep the knee stable while mobilising and epidurals can delay this by knocking out the muscular strength and feelings in the legs. A physio and an assistant gets the patient up walking for a short distance with a walking frame if they are older and with crutches if they are more stable. Operation instructions usually allow weight-bearing to facilitate normal muscle activity patterns and promote venous 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.

Physiotherapists will progress patients quickly on to gym exercises either singly or in a class, working on muscle strengthening via gym balls, Theraband resistance and functional exercises such step ups and sitting to standing. Resisted exercises, gentle stretches and static bicycling are used to increase knee flexion and balance related exercises such as the wobble board improve the patient's joint position sense, an important ability of the joint to know its spatial position, to restore normal joint functioning. The physio will correct abnormal gait and teach the appropriate walking pattern.