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Risk Factors for Infection After Total Knee Replacement

Infection after knee replacement surgery is a well-known risk and one everyone would like to avoid. In this study, surgeons from the Rochester, Minnesota Mayo Clinic get to the bottom of what causes infections serious enough to need surgery to treat them.

They looked at the records of over 17,700 patients to identify 1) how often does this happen (incidence), 2) what happens to these patients (long-term sequelae), and 3) what are the risk factors? They divided cases of infection into three groups of risk factors: patient-specific, surgical, and postoperative.

The goal was to find out what causes minor infections to become major ones later? Early problems reported were usually superficial (on the surface). The problem could be a failure of the incision to close, skin or scar infection, or continued drainage from the wound.

Conservative care was given at first. The wound was cared for and motion was limited that might aggravate the healing wound (including range-of-motion exercises and walking). Antibiotics were prescribed for some patients. Depending on how soon the diagnosis was made and how severe the infection was, the surgeon recommended topical, oral, or intravenous antibiotic therapy.

They found that minor, superficial wounds can progress to become deep infections requiring surgical treatment. This occurred less than one per cent of the time. Incidence (how often it happens) was very low, but still devastating for the patient. They used a 30-day time frame (infection occurred, progressed, and needed surgery within the first 30 days after the knee replacement).

In order to identify specific risk factors, they compared characteristics of the group with infection to the rest of the group who did not develop an infection. What is it that puts some patients at increased risk for infection that other patients without infection don't have?

Possibilities included body mass index (BMI measured at more than 30), history of previous knee surgery, diabetes, tobacco use, age, gender, and diagnosis. The various diagnoses included inflammatory arthritis, posttraumatic arthritis, and osteoarthritis (most common). Special note was made when patients had other health problems such as circulation problems, heart disease, diabetes, or steroid use.

Only 59 patients out of the more than 17,700 patients developed an infection serious enough to need surgical treatment. That translates to 0.33 per cent (much lower than even the one per cent figure mentioned earlier). Surgery included débridement (cleaning the wound) and/or cutting off the edge of the wound and restitching the skin together. In some cases, more extensive wound repair was done.

There was no obvious difference between the groups in terms of age, gender, or duration of follow-up. Likewise, cigarette smokers and patients who used steroids did not develop serious wound healing problems. And the type of arthritis (inflammatory, posttraumatic, or osteoarthritis) wasn't a risk factor either.

That left other health problems as a potential risk factor. Looking at each one of those, there were some statistics that suggested peripheral vascular disease (poor circulation to the hands and feet) might have a slight effect. The same was true for body mass index (BMI; slightly more infections occurred when BMI was greater than 30). But the real risk factor was diabetes. Patients with type two diabetes were much more likely to develop poor or delayed wound healing leading to superficial (and later deep) infection.

By following patients for up to five years after the knee replacement, the researchers were able to get an idea of how often deep infections occur as time went one. It turns out that some patients had a deep infection that was missed. The surgeon used clinical judgment that the infection was superficial (when it was really deep), rather than using a specific test (culture of the tissue) to find out if there was a significant infection.

The result of missing deep periprosthetic (around the implant) infections is that a simple treatment early on gets passed by. Eventually, the patient needs much more extensive surgery to take care of the problem. The missed diagnosis increases the risk that the patient could lose the implant. In a few cases, amputation was even necessary.

There were a few things this study did not look at. For example, how can you tell when a superficial wound needs surgical treatment and when can it just be treated conservatively? Secondly, how often does it happen that superficial wounds treated conservatively should have been surgically treated in those early days after surgery? The authors suggest that these two wound healing problems need a closer look in future studies.

Even though only one out of every 300 patients ended up with an infection, the long-term effects were serious. The authors encourage other surgeons to always make sure wound-healing takes place. Any signs of infection should be cultured and treated as soon as possible. Anyone with diabetes should be followed especially closely for early signs of infection or problems with wound healing.

Daniel D. Galat, MD, et al. Surgical Treatment of Early Wound Complications Following Primary Total Knee Arthroplasty. In The Journal of Bone and Joint Surgery. January 2009. Vol. 91A. No. 1. Pp. 48-54.


*Disclaimer:* The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic.
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