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.
Metal and plastic components are inserted to replace the degenerative joint surfaces of the knee. In knee replacement these consist of four items:
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 plastic insert, made of ultra high density polyethylene, is placed between the femoral and tibial inserts.
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.
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.
After individual work patients move on to gym based work, often in groups, to continue with strengthening muscles using gym balls or resisted rubber bands and dynamic activities such as standing up/sitting down and step-ups. Static bicycling and resisted exercises can be used to increase flexion further and training in joint position sense or proprioception is added. Proprioception is the ability of the joint to sense where it is in space, how fast it is moving and with what force, and is trained by balancing on a wobble board. Gait patterns are corrected and the physio teaches a normal pattern.
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