What is a total knee replacement?

A total knee replacement is a surgical procedure whereby the diseased knee joint is replaced with artificial material. The knee is a hinge joint which provides motion at the point where the thigh meets the lower leg. The thigh bone (or femur) abuts the large bone of the lower leg (tibia) at the knee joint. During a total knee replacement, the end of the femur bone is removed and replaced with a metal shell. The end of the lower leg bone (tibia) is also removed and replaced with a channeled plactic piece with a metal stem. Depending on the condition of the kneecap portion of the knee joint, a plastic "button" may also be added under the kneecap surface.

The posterior cruciate ligament is a tissue that normally stabilizes each side of the knee joint so that the lower leg cannot slide backward in relation to the thigh bone. In total knee replacement surgery, this ligament is either retained, sacrificed, or substituted by a polyethylene post. Each of these various designs of total knee replacement has its benefits and risks.

 

What patients should consider a total knee replacement?

Total knee replacement surgery is considered for patients whose knee joints have been damaged by either progressive arthritis, trauma, or other rare destructive diseases of the joint. The most common reason for knee replacement in the United States is severe osteoarthritis of the knees.
Regardless of the cause of the damage to the joint, the resulting progressively increasing pain and stiffness and decreasing daily function lead the patient to consider total knee replacement. Decisions regarding whether or when to undergo knee replacement surgery are not easy. Patients should understand the risks as well as the benefits before making these decisions.

What are the risks of undergoing a total knee replacement?

Risks of total knee replacement include blood clots in the legs that can tavel to the lungs (pulmonary embolism). Pulmonary embolism can cause shortness of breath, chest pain, and even shock. Other risks include urinary tract infection, nausea and vomiting (usually related to pain medication), chronic knee pain and stiffness, bleeding into the knee joint, nerve damage, blood vessel injury, and infection of the knee which can require re-operation. Furthermore, the risks of anesthesia include potential heart, lung, kidney, and liver damage.

What is involved with the preoperative evaluation for total knee replacement?

Before surgery, joints adjacent to the diseased knee are carefully evaluated. This is important to ensure optimal outcome from the surgery. Replacing a knee joint which is adjacent to a severely damaged joint may not yield significant improvement in function. Furthermore, all medications which the patient is taking are reviewed. Blood-thinning medications such as warfarin (Coumadin) and antiinflammatory medications such as aspirin may have to be adjusted or discontinued prior to surgery. Routine blood tests of liver and kidney function and urine tests are evaluated for signs of anemia , infection, or abnormal metabolism. Chest X-ray and EKG are performed to exclude significant heart and lung disease which may preclude surgery or anesthesia. Finally, it is less likely to have good long-term outcome if the patient's weight is greater than 200 pounds. Excess body weight simply puts the replaced knee at an increased risk of loosening and/or dislocation.

A similar risk is encountered in younger patients who may tend to be more active, thereby adding trauma to the replaced joint