Risks and Possible Complications

The two major complications that can cause failure of a total knee replacement are infection and loosening. Infection has a very small chance of occurring (1 out of 100 in first time knee replacements and 4 out of 100 for revision knee replacement), but if infection occurs it is a very difficult problem to treat. Most infections in total knee replacement occur due to contamination at the time of surgery or subsequent would breakdown. It is a myth that surgery can be a truly sterile procedure. Any time that people are in an operating room there will be small number of bacteria that can settle in the wound. We take a number of precautions to decrease the number to a minimum. These include the use of sterile instruments and drapes as well as gowns and masks and head covers.

The patients leg is thoroughly cleaned with an antiseptic agent and all other areas are covered with sterile drapes. In addition to these routine measures, the surgery is performed in an "ultra clean room" or "laminar air flow room". In this type of operating room a uniform flow of filtered air is continually circulated over the wound. "Space Helmets" (body exhaust filtration systems) are also worn by the surgical team. Another measure to decrease infection is the use of prophylactic antibiotics. This means to use antibiotics in advance to prevent an infection rather than to treat it after it occurs. Normally we use antibiotics during surgery and for 48 hours after surgery.

If an infection occurs in a total knee, every effort is made to retain the prosthesis but this is successful less than 20% of the time. If the implant is loose or if the infection continues to reoccur, it is usually necessary to remove the implant completely in order to cure the infection. This, of course, leaves the patient without a knee joint, and although walking is possible, usually two crutches are required, the leg requires a brace and motion is minimal. At least six weeks of intravenous antibiotics are required to treat the infection. After the infection is cured, consideration can be given to reimplantation of a total knee but statistics show that 10% of reimplantation cases develop infection again. Because of this high recurrent rate, knee fusion is sometimes considered as an alternative to replacement of the artificial knee.

The second major complication is that of loosening. The key to success for total knee replacement is that all motion should occur between inert materials (i.e. metal and plastic). If the implant, loosens from their boney attachment, the motion between bone and implant will cause pain, bone destruction and ultimate failure. Loosening usually takes several years to develop and can occur as late as 10 to 15 years for a cemented implant.
The process of loosening is attributed to failure (cracking) of the cement used to anchor the implant to the bone. It is felt that this cracking is a "fatigue failure" caused by multiple repetitive loads or loads that are excessively high in certain areas.

The risk of loosening in ideal candidates is approximately 3% in 10 to 15 years. In non-ideal candidates such as patients with excessive body weight and younger, more active patients as well as patients who have had a previously failed cemented implant, the chance of loosening increases.

Other possible complications need to be mentioned. Instability can occur due to poor ligament balance. This can cause buckling when weight bearing and may require the use of a knee brace and/or cane. Usually it is not painful. Rarely is revision surgery needed to correct this problem. Instability is relatively rare with only 1-2% having a functional problem.
The knee cap may fail to track properly in it's groove (patellar tracking problems) in 1-5% of patients. This results in a jumping or snapping of the knee cap when the knee is bent. Occasionally complete dislocation can occur. Usually knee cap tracking problems can be managed with exercises and the use of an elastic sleeve. Sometimes corrective surgery is required.

Poor motion of the knee after surgery is another risk. Over 90% of patients after total knee replacement will be able to extend the knee and bend it beyond 90 . In a small percentage of patients internal scarring can result in reduced motion and some pain.

Another complication that may occur is formation of blood clots in the legs or pelvis. There are two potential problems that can result from blood clots: Chronic swelling in the affected leg and serious complications if the clots travel to the lungs (pulmonary embolism). If this occurs, it can be life threatening.

Four different preventative measures can be taken to decrease the risk of blood clot formation. The first is the use of a blood "thinner" (anti-coagulation) like Coumadin in low doses. The second is the use of spinal or epidural anesthesia (sometimes in conjunction with general anesthesia). Third, mechanical pumps (compression stockings) can be used. Finally, early mobilization beginning on the first day after surgery and active in bed exercises such as ankle "pumps" are a helpful. Several of these measures may be used in combination resulting in a less than 10% chance of developing blood clots and a chance of a pulmonary embolus less than 3%. The chance atal pulmonary embolus with this regimen is 1 in 5000.

Other risks of which you should be aware of are: anesthetic risks, the strain of surgery on the heart and lungs, and possible damage to nerves, arteries and veins which can affect the circulation and the function of the leg. All of these occur less than 1% of the time.

Revision total knee replacements require special mention. A revision is defined as a total knee replacement done for a previously failed implant. The chance of success in revision knee replacement is only 80% as compared to 95% for primary procedures. The rate of developing an infection is increased to 4%. Usually the cause for failure has been loosening of the implant from the bone.

We have gone over all of these complications in some detail not to frighten you intentionally, but to inform you of the possible risks of the procedure. Taken in total, the risks are usually quite low and the chances of success greatly outweigh a chance of failure.