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.

Total knee replacement is one of the most successful medical technologies with the highest quality of life improvements of any medical intervention, a distinction it shares with total hip replacement. Knee replacement has matured from an experimental procedure of uncertain long-term outcome to a predictable and very common operation with very good results at ten years or more. As western populations age knee replacement is overtaking hip replacement as the most commonly performed joint replacement.

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

* The metal femoral insert to replace the lower end of the femur which is the top half of the knee.

* 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.

The components are fixed in place using cement which acts as a grouting material rather than sticking anything. 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.

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.

Mobilisation of the patient is the next process in rehabilitation. The physiotherapist assesses the patient’s medical status and examines the legs to decide whether mobilisation is appropriate and safe. The quadriceps must be working well enough to provide some knee stability and epidurals can interfere with this for long enough to delay getting up until the effects have worn off. The physio and an assistant get the patient up and establish a good walking pattern with crutches, or a frame for much older people. Normal weight-bearing is usual and this re-establishes normal stresses through the knee, encouraging circulatory return from the leg and normal muscular activation.

After discharge the physiotherapist will work on increasing joint range of motion, improving functional skills and improving muscular power and control of the knee. Typical exercises include knee flexion exercises to increase movement, inner range quadriceps for quads strength into extension and knee hangs to increase extension. Resisted work to the hamstrings uses reciprocal inhibition, the technique whereby working one muscle relaxes the antagonists, in this case increasing knee bend. Physios can do this manually or use resistance bands and encourage soft tissue massage to the scar to mobilise the tissue.

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.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about physiotherapy, physiotherapy, physiotherapists in Leeds, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.