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.

Medical technology developed in the late twentieth century to the stage that joint replacement has become a common and predictable treatment for severely arthritic joints, proving to give the highest quality of life of all medical interventions. Total knee replacement is now a predictable and very successful intervention with good ten year results and beyond. Knee replacement is becoming a more popular operation than hip replacement and as western populations get older the demand will increase.

The total knee replacement operation replaces the diseased surfaces of the knee with metal or plastic parts. In the case of the knee there are typically four parts:

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

The metal tibial insert to replace the tibial surfaces, the lower half of the knee.

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

A plastic button which fixes on to the posterior surface of the patella, without which some patients continue to complain of anterior knee pain after replacement.

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.

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.

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.