Knee replacements are increasingly common as the population becomes more active, incurring sports injuries which later develop into osteoarthritis. The knee joint is not as strong as the hip joint, and even slight cartilage degeneration can put substantial stress on the knee. This causes pain and bowlegged or knock-kneed deformity.
For some patients, osteoarthritis can occur in both knees. While it is possible to replace both joints during the same operation, PAMF surgeons generally recommend doing one leg at a time in two separate surgeries, scheduled several months apart. This puts less stress on the patient's body during the procedure and in postoperative physical therapy.
The modern knee replacement procedure, known as "total condylar knee replacement," was first performed in the 1970s. Bone and cartilage at the lower end of the femur (upper leg bone) and upper end of the tibia (shin bone) are removed and replaced with prosthetic components. The kneecap may also be replaced. As in hip replacements, the artificial knee is made up of cobalt chrome, titanium and polyethylene plastic. These parts are generally cemented in place, although surgeons may choose to use an "ingrowth" procedure, in which bone grows between small beads of mesh on the surface of the prosthetic components. The surgeon may also substitute the posterior cruciate ligament, which helps hold the knee in place.
Knee replacement surgery is done through an incision in the front of the knee, which is generally about eight inches long and later closed by sutures or staples. The operation lasts between 45 and 90 minutes, depending on the patient's size (larger knees take more time to replace) and whether cement is used (so that the cement has time to dry). If both knees are replaced at the same time, the procedure takes longer. For more information about surgery and recovery, please visit the Patient Care Process page.
Therapy involves strengthening and range-of-motion exercises, including bending the knee repeatedly. After four to six weeks, patients should be able to bend their knee past 90 degrees, and by 12 weeks patients should be well on their way to recovery.
Even after recovery, patients are generally aware of the knee replacement's presence. Many report that the artificial joint feels "mechanical" and clicks when it moves. But these sensations are not painful and often have the side benefit of reminding people to take care of their new joint, so that it lasts longer. As with hip replacements, light activities such as walking, doubles tennis, stationary bicycle riding and golf are fine for knee replacement patients. Higher-impact activities such as basketball and downhill skiing should be avoided, as they can loosen or break the prosthetic knee.
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