Knee Replacement

The knee joint is composed of the large thigh bone called the femur and the large bone in the lower leg called the tibia.  In a total knee replacement, the end of the femur bone is replaced with a metal shell and the end of the tibia is removed and replaced with a channeled plastic prosthesis with a metal stem.  Cemented, cementless, and hybrid procedures are available for the fixation of the prosthesis.  Cement fixation is the most common.   

Who is a candidate for a total knee replacement?

People who suffer from severe symptoms that interfere significantly with quality of life and who have failed conservative treatments are potential candidates for total knee replacement surgery.  Conservative therapy may include medications, injections of corticosteroid, injections of hyaluronic acid, activity modification, walking aids, acupuncture, and physical therapy.  People who would otherwise be candidates for total knee replacement may not be appropriate candidates if they have other medical conditions that make surgery too dangerous.

What are the potential risks and complications of a total knee replacement surgery?

            There are risks to any surgery, including the risk of general anesthesia.  Risks of general anesthesia are rare but include heart attack, pneumonia, stroke, liver toxicity, and death.           A rare but serious potential complication of total knee replacement surgery is the risk of developing a clot in your leg called a deep vein thrombosis (DVT).  If this clot becomes dislodged, it can potentially travel to your lungs causing a pulmonary embolus (PE) which compromises the ability for your lungs to take in oxygen.  A clot can also travel to the brain causing a stroke.  Between 47% and 64% of patients who are not given blood thinners after total knee replacement surgery will develop a blood clot.  That number drops to 6% to 24% when patients receive blood thinners.  For a patient who is not a candidate for taking blood thinners because of other medical problems, a filter can be put in front of the lungs to keep clots from spreading to the lungs. 

Other potential complications from a total knee replacement surgery include infection, bleeding, and chronic knee pain.  It is important to have a detailed discussion with your doctor about all of the potential risks and complications before undergoing any surgical procedure.

What does the rehabilitation process involve after total knee replacement surgery, and when does it begin?

            The rehabilitation process begins as early as the first day after surgery.  After a total knee replacement, patients begin gradual rang-of-motion exercises, strengthening exercises, and progressive ambulation is begun.  Initially, patients will use a rolling walker to aid ambulation.  Patients then typically progress to using a cane and then will not require an assistive device for walking.  Patients will also gradually progress to going up and down stairs.  If a cemented prosthesis is used, the patient is generally able to put as much weight on the affected limb as tolerated immediately after surgery.  If a cementless procedure is used, the patient is generally only allowed to put 20% or less of their body weight on the affected limb for 6 weeks after surgery.  After 6 weeks, an x-ray is obtained and a decision is made by the orthopedist if the patient is able to place more weight on the affected limb. 

            Continuous passive motion (CPM) machines are often used after surgery.  CPM machines move the affected limb passively through a specified range of motion while the patient relaxes.  CPM machines may facilitate recovery by encouraging a quicker return to full range of motion after surgery.  Patients need to reach approximately 90 degrees of knee flexion to be able to return fully to activities of daily living, particularly those activities that require sitting and climbing stairs.   Once discharged from the hospital, patient continue to participate in a structure physical therapy program as an outpatient.  If a cemented prosthesis is used, patients can anticipate a gradual return to full activities over the course of 1 to 3 months.  If a cementless procedure is used, the recovery process will take longer.