The knee is the largest joint in the body; it joins the thigh with the lower leg. Each knee bears half the weight of the body. We depend on our knees to go about all our day-to-day activities. A smooth layer of cartilage, which allows for movement and rotation, covers the lower part of the thigh-bone (femur) and the upper part of the shin-bone (tibia).
The underside of the kneecap or patella is also covered in cartilage. This allows it to slide in the groove on the front of the femur. If these surfaces are eroded due to injury or wear, they become rough and uneven. The joints can no longer move smoothly. This friction of the bones causes extreme discomfort and pain, making it very difficult to walk or climb stairs. A total knee replacement removes the damaged joint and replaces it with an artificial joint. The operation is a standard procedure, which can take between one and three hours in the theatre.
Physical therapy is a very important part of the rehabilitation process after a total knee replacement and can begin as soon as 48 hours after surgery. The continuous passive motion (CPM) machine is a device that can speed up the rate of recovery during this first phase of rehabilitation.
The operated leg is attached to the CPM machine, which slowly and continuously moves the leg through a range of movements while the patient relaxes. The machine can be administered for hours at a time.
The gentle manipulations by the CPM machine can help prevent joint stiffness, which is a persistent problem after surgery. It can also help decrease swelling and pain as well as reduce scarring. There is also evidence to suggest that patients who use CPM following knee replacement surgery are less likely to require knee manipulation, where the patient’s knee has to be forced into flexion under general anaesthesia.