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AAOS Now

Published 4/1/2012

RSA patients with positive intraoperative cultures at low risk for recurrent infection

Study results suggest prolonged antibiotic therapy may not be necessary

Maureen Leahy

Patients undergoing one-stage revision shoulder arthroplasty (RSA) who had positive intraoperative cultures, but were not treated with long-term postoperative antibiotics for infection, are at low risk for recurrent infections. This suggests that postoperative antimicrobial treatment strategies may not be necessary in these patients.

The study results were presented by Matthew J. Grosso, BS, of the Cleveland Clinic Lerner College of Medicine, during the American Shoulder and Elbow (ASES) Specialty Day.

Although intensive antimicrobial strategies such as component removal or long-term antibiotic therapy may appear appropriate, very little information exists on treatment strategies for RSA patients who have a subclinical or indolent infection, Mr. Grosso said. “The purpose of our study, therefore, was to determine infection recurrence rates for patients undergoing RSA with positive intraoperative cultures who were not treated for infection. We hoped to help determine an appropriate treatment strategy for this patient population.”

Retrospective analysis
Mr. Grosso and his colleagues retrospectively reviewed data on 187 patients who underwent RSA performed by a single surgeon between 2001 and 2009. They identified a subclinical infection cohort (n = 17; males = 13; average age = 66 years) that included patients with at least one positive intraoperative culture but no clinical signs or diagnostic markers of infection.

Six of the 17 patients had cultures that were identified as contaminants by microbiology—growth of an organism on a nonspecific plate or bacterial growth in thioglycolate broth. “We chose to include these patients in our cohort because previous studies were not clear about what can be defined as a contaminant,” Mr. Grosso said.

All 17 patients underwent single-stage RSA (7 after total shoulder arthroplasty [TSA]; 8 after reverse TSA; 2 after hemiarthroplasty). Surgery included extensive irrigation and débridement, implant and cement removal, and placement of revision-cemented components. Thirteen patients (76 percent) received antibiotic-impregnated cement (tobramycin or gentamicin). Although each patient received routine intravenous (IV) antibiotics for 24 hours postoperatively, none of the patients received extended postoperative IV antibiotic therapy.

The researchers reviewed the patients’ chart data to determine the following:

  • rates of reinfection
  • pathogen species
  • preoperative laboratory values for erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and white blood count
  • tissue histology
  • major complications
  • functional outcomes

Reinfection rates low
The mean postoperative follow-up was 35.8 months (range: 22–84 months). Recurrence of infection was determined by postoperative positive cultures or clinical signs of infection such as drainage, swelling, erythema, or purulent material. Within the cohort, a subsequent clinical infection developed in only 1 patient (5.9 percent). This patient’s culture was originally labeled as a contaminant, which supported the researchers’ decision to include these patients in their study, noted Mr. Grosso.

The most common pathogen was Propionibacterium acnes (56 percent), followed by coagulase-negative Staphylococcus species (35 percent). All patients had ESR and CRP readings within normal levels. Aside from reinfection, the only other complication was a single case of radial nerve entrapment and palsy.

“We found that low virulence and clinically unexpected infections identified during one-stage revision and treated simply with routine postoperative antibiotics have a low risk for recurrent infection,” summarized Mr. Grosso.

Long-term therapy has risks
To examine the risks associated with long-term antibiotic therapy, the researchers also analyzed the complications in 31 two-stage RSA patients who were treated for clinical infections with at least 6 weeks of antibiotic therapy after the first stage. They discovered that 6 patients (16 percent) had minor complications related to the antibiotic therapy and that one patient had acquired a Clostridium difficile infection.

“Our study suggests that intensive antimicrobial treatment strategies—which are associated with significant costs and risks—may not be necessary to reduce recurrent infections in patients with positive intraoperative cultures but no overt signs of infection,” Mr. Grosso said. “However, further prospective studies comparing reinfection rates in treated versus nontreated groups are needed to confirm these findings.”

Mr. Grosso’s coauthors of “Reinfection rates after 1-stage revision shoulder arthroplasty for patients with unexpected positive intraoperative cultures,” are Vani J. Sabesan, MD; Jason C. Ho, MS; Eric T. Ricchetti, MD; and Joseph P. Iannotti, MD, PhD.

Disclosures: Dr. Sabesan—Ruth Jackson Orthopaedic Society; Dr. Iannotti—DePuy, A Johnson & Johnson Co.; Biomet, Inc.; Tornier, Inc.; Wyeth; Wolters Kluwer Health/Lippincott Williams & Wilkins; Journal of Shoulder and Elbow Surgery; Dr. Ricchetti, Mr. Grosso, and Mr. Ho—no conflicts.

Bottom Line

  • Little information is available to guide treatment strategies for RSA patients with positive intraoperative cultures but no overt signs of infection.
  • This retrospective case review analyzed infection recurrence rates for patients undergoing RSA with positive intraoperative cultures who were not treated for infection.
  • Low virulence and clinically unexpected infections identified during one-stage revision surgery and treated only with routine postoperative antibiotics (24 hours) were found to have a low risk for recurrent infection.
  • Intensive antimicrobial treatment strategies may not be necessary to reduce recurrent infections in RSA patients with positive intraoperative cultures but no overt signs of infection.