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Examine pre- and intraoperative factors to help evaluate positive cultures in patients
Labeled bone scans can yield a high negative predictive value and help to rule out infection.
Using a multifactorial approach may help surgeons better predict infection in revision total joint replacement patients with positive preoperative and intraoperative cultures.
“It turns out that if you look at the current literature, that much of what we have been taught about diagnosis of infection is, in fact, open to question now,” Norman A. Johanson, MD, said during his presentation at the 8th Annual Advances in Arthritis Arthroplasty and Trauma Course Lecture. “There is really no gold standard out there, especially just one isolated positive culture that can bring us to a diagnosis of an infection.”
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Criteria for infection
Johanson cited work by Javad Parvizi, MD, FRCS, which defined infected arthroplasty patients as having three of the five following criteria:
- a C-reactive protein (CRP) level of >1 mg/dL;
- an erythrocyte sedimentation rate (ESR) >30 mm/hr;
- a positive joint aspiration culture;
- purulent looking intraoperative tissue; or
- a positive intraoperative culture.
“I think that the message that these criteria give us is that we should evaluate our clinical suspicion and that starts with a history,” Johanson said. He noted the following conditions as red flags for infection:
- poor wound healing after a primary procedure;
- intermittent drainage in or surrounding the scar;
- persistent drainage for at least a week following the primary operation;
- unrelieved pain; and
- pain at rest.
Surgeons should also ensure that radiographs correspond with the patient’s clinical history.
Screening
In cases with positive postoperative cultures, surgeons should consider test sensitivity, specificity, accuracy and positive and negative predictive values. Joint aspiration should be reserved for patients with an elevated suspicion for infection due to the chance of false positives, Johanson said.
He cited research by Mark J. Spangehl, MD, which used aspiration as a screen for infection. While Spangehl found a 17% infection rate, he found a positive predictive value (PPV) of 67% due to contamination. However, in a study of 168 patients with a confirmed infection rate of 57%, Parvizi found a PPV of 100% for aspiration.
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“This shows that if you have a population of higher-suspicion patients, the predictive value of your test is going to be improved,” Johanson said.
He noted that white blood cell counts of >1,760 cells/10-3L or neutrophils >73% can also yield high PPVs in populations with a high suspicion for infection. Technetium-99-m and Indium-111 scans can help rule out infection in ambiguous cases and show negative predictive values of 88% and 95%, respectively, Johanson said.
Surgeons should not perform joint aspirations in cases with normal X-rays, histories, physical exams, ESR and CRP levels, or those with identified causes of mechanical failure. “But, if you have anything like a positive culture, the Technetium and Indium label bone scans will be helpful. If both of the repeat culture and scans are negative, you could safely go ahead and continue with your low suspicion scenario and go into the surgery pretty confident,” Johanson said.
Intraoperative gram stains are not useful and using the appearance of the tissue to diagnosing infection should only be used adjunctively, he said. Intraoperative frozen sections are best used for critical decisions such as implant removal, debridement and one or two stage exchanges.
“However, most studies will tell you that less than 5 neutrophils per high-powered field is a pretty safe bet it is not infected, but the 5 to 10 grey zone is still something that you are going to have to work out between yourself, your own pathology department and possibly your infectious disease specialist,” Johanson said. “Over 10 per high-powered field is a pretty good positive predictive value for infection.”
A note from the editor:
In September, Javad Parvizi, MD, FRCS, will begin a bi-monthly column for Orthopedics Today called Infection Watch.
For more information:
- Norman A. Johanson, MD, can be reached at Drexel University College of Medicine, 245 N 15th Street, Room 7209; Philadelphia, PA 19102; 215-762-1954; e-mail: Norman.A.Johanson@drexel.edu. He receives royalties from Exactec and is and independent research contractor for Isotis.
References:
- Johanson, NA. Dealing with the positive culture before and after the procedure. #97. Presented at the 8th Annual Advances in Arthritis Arthroplasty and Trauma Course Lecture Summaries. Sept. 27-30. Arlington, VA.
- Parvizi J, Ghanem E, Menashe S, Barrack RL, Bauer TW. Periprosthetic infection: what are the diagnostic challenges? J Bone Joint Surg (Am). 2006;88 Suppl 4:138-147.
- Spangehl MJ, Masri BA, O’Connell JX, Duncan CP. Prospective analysis of preoperative and intraoperative investigations for the diagnosis of infection at the sites of two hundred and two revision total hip arthroplasties. J Bone Joint Surg (Am). 1999;81(5):672-683.