Preventing Joint Infection After Knee Replacement

Surgeons looking for ways to prevent infections in patients receiving a knee joint replacement will find this article of interest. Presented as an instructional course, the authors provide information on the incidence of periprosthetic infections, risk factors, diagnosis of infection, and management of the problem.

Periprosthetic infection refers to infection in and/or around the implant and joint in which the implant is located. Most of the infections are caused by staphylococcus aureus more commonly known as a "staph" infection.

Up to two per cent of the adults receiving a knee replacement will develop a periprosthetic infection. That number includes those patients who are diagnosed with an infection early on (first year after the procedure) as well as infections reported 10 years later.

Two per cent might not sound like much -- and, in fact, it really isn't a common complication. But there are two things that make this problem a problem. First, it can be difficult to diagnose and treat. A second surgery may be needed. Some patients end up having multiple revision surgeries.

And second, with the millions of Baby Boomers (born between 1946 and 1964) reaching senior status, it is expected that the number of knee replacements done in a year will rise significantly. That all means a two per cent rate could actually equal many thousands of patients affected each year.

The need to prevent periprosthetic infections is obvious. The way to do it is not so clear. Surgeons and patients both have a part in this potential problem. On the surgical side, it has been recommended that patients receive antibiotics one hour before the surgery begins.

Although staph infections can be picked up while in a hospital, many patients actually come to the hospital with their own bacteria because they are carriers and infect themselves. The prophylactic (preventive) antibiotics given before surgery help reduce self-infection. For the same reason, implants are coated with an antibiotic.

Patients who smoke, drink alcohol excessively, or who are obese are also at increased risk for periprosthetic infection. You might not think overweight or obese patients can be malnourished but the quality of what they eat isn't always nutritional. Blood tests can help identify patients who are at risk for infection based on a poor nutritional status.

Malnutrition, urinary tract infection, and a history of diabetes, cancer, and rheumatoid arthritis are risk factors linked with joint infections after knee replacement. Anyone with a blood clotting disorder or taking medications to reduce clot formation (anticoagulants) must be watched carefully as well.

How does a patient know if his or her knee implant is infected? The first symptoms are constant knee pain, stiffness, and loss of knee motion. The presence of any risk factors raises the suspicion of infection.

Blood tests help confirm the diagnosis. The authors provide a detailed discussion of lab values used to assess patients for infection. Using inflammatory markers in the blood isn't a cut and dried process. Early on after surgery, there are always increased levels of inflammatory cells as the body works to heal the surgical area. There's a fine line between normal and abnormal elevation of blood markers.

Once it looks like an infection might be present, the surgeon removes a bit of fluid from the joint and has that analyzed. The results of the fluid culture may support a diagnosis of infection. But the surgeon knows that there can be false-negatives (i.e., test comes back negative when there really is an infection).

Antibiotic treatment is the first-line approach to management of periprosthetic infections following total knee replacement. Surgery is often a part of the plan of care as well. The surgeon cleans the joint out of any infection (a procedure referred to as debridement.

Any affected component parts of the implant are removed. Sometimes the entire implant has to be taken out. Repeated episodes of debridement are done until the joint culture test results come back normal once again. During that time, the surgeon puts in a spacer in place of the infected joint implant.

Once everything is cleared up and the cultures come back negative, then the surgeon inserts a new implant. Follow-up care includes continued antibiotics and close observation. Studies show a high rate of success with this protocol. Patients experience good long-term results with pain free, full, and smooth range-of-motion.

Reference: Kevin L. Garvin, MD, and Beau S. Koningsberg, MD. Infection Following Total Knee Arthroplasty. in The Journal of Bone & Joint Surgery. June 2011. Vol. 93A. No. 12. Pp. 1167-1175.

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