The Journal of Arthroplasty Vol. 14 No. 8 1999 The Role of Intraoperative Gram Stain in the Diagnosis of Infection During Revision Total Hip Arthroplasty Mark J. Spangehl, MD, FRCS(C),* Eric Masterson, BSc, MCh, FRCS(Orth),* Bassam A. Masri, MD, FRCS(C),t John X. O'Connell, MB, FRCP(P),~: and Clive P. Duncan, MB, MSc, FRCS(C)t Abstract: A total of 202 revision hip arthroplasties in 178 patients, over a 2-year period, were evaluated prospectively. Intraoperative Gram stains were obtained from periprosthetic tissues in all cases. Of these, a definitive diagnosis of infection, using defined criteria, was established in 35 cases. Of these 35 patients, 17 had received antibiotics before surgery. The intraoperative cultures were positive in 8 of the 17 patients who had received antibiotics and 17 of the 18 patients who had not received preoperative antibiotics. In 1 infected case, intraoperative cultures of periprosthetic tissues failed to reveal bacterial growth, despite the fact that the patient received no preoperative antibiotics. Overall, there were 5 true-positive Gram stain results, 172 true-negative results, 3 false-positive results, and 22 false-negative results. The sensitivity of the Gram stain was 19%, specificity was 98%, predictive value of a positive test was 63%, and predictive value of a negative test was 89%. These results suggest that the intraoperative Gram stain is not a sensitive tool for the diagnosis of infection and should not be used when attempting to diagnose infection intraopera- tively. Key words: Gram stain, infection, failed arthroplasty. The single most important factor in determining treatment options for the failed hip arthroplasty is the diagnosis or exclusion of infection. In most cases, a diagnosis of infection can be successfully made preoperatively based on a combination of clinical presentation, radiographs, laboratory inves- tigations, and hip joint aspiration. Uncommonly, radionuclide imaging may be of value. In other cases, the diagnosis can be established by the pres- ence of pus in the joint at the time of revision surgery. There are a number of patients with failed From the *Department of Orthopaedics, the ~Division of Reconstruc- tive Orthopaedics, and the ~Department of Pathology, University of British Columbia, Vancouver, British Columbia, Canada. Submitted June 8, 1998; accepted March 16, 1999. No benefits or funds were received in support of this study. Reprint requests: Mark J. Spangehl, MD, FRCS(C), 102-65 Richmond Street, New Westminster, BC, V3L 5P5 Canada. Copyright © 1999 by Churchill Livingstone ® 0883 -540319911408-0010510.00/0 hip prostheses, however, in whom the preoperative assessment does not definitely exclude or diagnose infection and in whom the intraoperative appear- ance of the tissues is equivocal. Development of a reproducible intraoperative investigation that al- lows the surgeon to differentiate between septic and aseptic loosening in these equivocal cases is re- quired. The only widely available tests that analyze the periprosthetic tissues, within an acceptably short time-frame, are an intraoperative frozen section, which shows histologic evidence of acute inflamma- tion, and an intraoperative Gram stain, which iden- tifies the presence of bacteria in the tissues or joint fluid. A considerable body of literature exists that as- sesses the role of intraoperative frozen section and concludes that this test is useful [1-3]. There is a paucity of information, however, regarding the utility of the Gram stain in the intraoperative 952