The knee is a hinge joint where the thigh bone (femur) and the bone of the lower leg (tibia) meet. Arthritis (particularly osteoarthritis) and certain knee injuries and diseases can damage the cartilage that normally cushions the joint, leading to pain and stiffness. A knee replacement may be recommended when more conservative treatments — such as anti-inflammatory medications and cortisone injections — fail to relieve pain or improve movement.
During a total knee replacement, the entire joint is replaced with an artificial prosthesis. The end of the femur is replaced with a metal shell. Then the end of the tibia is fitted with a plastic cup and a metal stem that fits into the shell on the femur. This reduces friction in the joint, easing pain and allowing a greater range of movement. The main ligament of the knee (the posterior cruciate ligament) may be left in place, removed or replaced with an artificial post. The kneecap may also be replaced with, or supported by, a piece of plastic. The surgery itself lasts between one-and-a-half and three hours.
After the procedure, the patient rests in a recovery room and then in a hospital room. Patients usually experience immediate relief from the joint pain suffered before the replacement. However, there will be some post-operative discomfort. Physical therapy starts right away to speed healing and to ensure that the patient enjoys full use of the joint. Therapy progresses from use of walkers and crutches to walking on stairs and slopes, with home exercises to supplement formal sessions. In addition, continuous passive motion (CPM) machines can reduce recovery time and the risk of muscle contracture without straining the joint.
Knee replacements today last about 20 years in 85-90% of well-selected patients.