The role of intraoperative Gram stain in the diagnosis of infection duringrevision total hip arthroplasty

A total of 202 revision hip arthroplasties in 178 patients, over a 2-year p eriod, were evaluated prospectively. Intraoperative Gram stains were obtain ed from periprosthetic tissues in all cases. Of these, a definitive diagnos is of infection, using defined criteria, was established in 35 cases. Of th ese 35 patients, 17 had received antibiotics before surgery. The intraopera tive cultures were positive in 8 of the 17 patients who had received antibi otics and 17 of the 18 patients who had not received preoperative antibioti cs. In I infected case, intraoperative cultures of periprosthetic tissues f ailed to reveal bacterial growth, despite the fact that the patient receive d no preoperative antibiotics. Overall, there were 5 true-positive Gram sta in results, 172 true-negative results, 3 false-positive results, and 22 fal se-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 shoul d not he used when attempting to diagnose infection intraoperatively.