AAOS issues clinical guidelines for diagnosing hip, knee periprosthetic joint infections

Robert L. Barrack

When diagnosing periprosthetic joint infections of the hip and knee, practitioners should begin with a simple blood test and withhold antibiotics until after obtaining culture results, according to new practice guidelines released by the American Academy of Orthopaedic Surgeons.

Among the 15 evidence-based recommendations included in the American Academy of Orthopaedic Surgeons (AAOS) guidelines are that joint aspirations should vary depending on the location of the arthroplasty, either hip or knee, and that probability of infection be based on established risk factors, including patient history.

“I would say these guidelines are long overdue and will be helpful,” said Robert L. Barrack, MD, a professor of orthopedics at Washington University School of Medicine in St. Louis. “For example, for well over 10 years now, there have been problems accurately diagnosing knee aspiration because such a high percentage of our patients have been placed on antibiotics. In short, you want to make an accurate diagnosis as quickly as possible.”

One of the challenges of diagnosing infected total joints “is that most of the time they are low grade and insidious. Patients just present with unexplained pain,” Barrack told Orthopedics Today. “Most people think that if you have an infection deep in your hip or knee, it will be accompanied by fever, chills and other classic signs of infection. But the fact is that well under 10% of patients present with a fever or obvious signs of infection. Usually they simply have pain.”

As the guidelines recommend, Barrack routinely performs a blood test for erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), for which the chance of infection is low when both ESR and CRP are normal.

Multiple cultures

Furthermore, for patients being evaluated for periprosthetic joint infections in preparation for revision surgery, multiple cultures should be obtained. “A single culture can be misleading because when you take fluid or tissue from a joint and send it to the laboratory, there are several steps along the way during which the specimen can become contaminated – from the back table of the operating room to in the lab itself. Bacteria can fall from the air or from the technician handling the tissue,” Barrack said. “Contamination probably occurs more than 10% of the time. Therefore, the best thing to do is collect four or five cultures.”

Securing frozen sections of tissues adjacent to the implant, when infection has not already been established or excluded, is also important. “This is a helpful tool, although not 100% accurate,” Barrack said. “We found that taking antibiotics can suppress growth on culture media for even longer than 6 weeks. And in about 5% of cases, you never do grow anything. Most often it is because people have been on antibiotics.”

Barrack also found that gram stains are not nearly as accurate for diagnosis as previously thought.

Delayed antibiotics

Craig J. Della Valle, MD, an associate professor of orthopedic surgery at Rush University Medical Center in Chicago, was chair of the physician work group that developed the guidelines. In an AAOS press release, he underscored the importance of delaying antibiotics. “The first rule of treatment in medicine is always to make the diagnosis first,” Della Valle stated. “Unfortunately, we often see patients who are given antibiotics prior to having appropriate cultures drawn from within the joint that can lead to a delay in diagnosis and a subsequent delay in appropriate treatment. Further, identification of the specific bacteria which is causing the infection is important in administering the most effective antibiotic to cure the infection. If antibiotics are given before we can get a good culture, we may not have the advantage of knowing exactly which antibiotics to give as the cultures can turn negative even after a single dose of antibiotics.”

Because any single orthopedic surgeon is unlikely to encounter many cases of periprosthetic joint infections, “it is probably easier to treat with a team of specialists, including a total joint specialist, an infectious disease specialist and a plastic surgeon,” Barrack said. – by Bob Kronemyer

Robert L. Barrack, MD, can be reached at Washington University School of Medicine, 660 S. Euclid Ave., Campus Box 8233, Department of Orthopedic Surgery, St. Louis, MO 63110; 314-727-2592; e-mail: barrackr@wustl.edu.

Craig J. Della Valle, MD, can be reached in the Department of Orthopaedic Surgery, Rush University Medical Center, 1725 West Harrison, Suite 1063, Chicago, IL 60612; 312-432-2350; e-mail: craigdv@yahoo.com.

Javad Parvizi

The recently released guidelines from the AAOS on diagnosis of periprosthetic joint infection (PJI) is the result of many months of work by the AAOS staff and volunteer experts who evaluate all relevant literature pertinent to the topic and devise guidelines based on available evidence. These guidelines are extremely important and timely. The incidence of PJI is on the rise and this dreaded complication poses a real challenge to the orthopedic community. In addition, there is emerging evidence that some of the so called “aseptic” failures are indeed infections that have escaped the available diagnostic modalities for PJI.

The AAOS workgroup under the leadership of Craig Della Valle, MD, has put together practical and step-by-step guidelines that, in my opinion, will lead to better patient care and reduced cost. The members of the AAOS staff and the volunteer experts should be congratulated for producing one of the most critical and relevant guidelines for the fellowship and the other physicians engaged in the care for patients with failed arthroplasty.

– Javad Parvizi, MD, FRCS
Member of the AAOS physician work group
Editor, Orthopedics Today Infection Watch column

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