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The Value of Intraoperative Gram Stain in Revision Total Knee Arthroplasty

¹ Department of Orthopaedic Surgery, Washington University School of Medicine, One Barnes-Jewish Hospital Plaza, 11300 West Pavilion, St. Louis, MO 63110. E-mail address for R.L. Barrack: barrackr{at}wustl.edu
² Rothman Institute of Orthopaedics, Thomas Jefferson University Medical School, 925 Chestnut Street, Philadelphia, PA 19107

Investigation performed at the Washington University School of Medicine, St. Louis, Missouri, and Thomas Jefferson University Medical School, Philadelphia, Pennsylvania

Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from Stryker Orthopaedics, Smith and Nephew Orthopaedics, and the Orthopaedic Foundation at the Rothman Institute. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. A commercial entity (Stryker Orthopaedics) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated.

Methods: We retrospectively reviewed the records on 945 revision total knee arthroplasties performed at three university institutions to which patients were referred for total joint arthroplasty; the results of an intraoperative Gram stain were available for review in 921 cases (97.5%). Of these knees, 247 were classified as infected on the basis of (1) the presence of the same organism in two cultures; (2) growth, on solid media, of an organism as well as other objective evidence of infection; (3) histologic evidence of acute inflammation; (4) gross purulence; and/or (5) an actively draining sinus. We reviewed the results of preoperative laboratory studies, which included measurements of the erythrocyte sedimentation rate, C-reactive protein values, and white blood-cell count in 90%, 76%, and 98% of cases, respectively. Preoperative aspiration to obtain a specimen for culture and a cell count was performed routinely at one center and selectively at the other two centers, and the results were available for review in 439 (48%) of the 921 cases.

Results: Intraoperative Gram staining was found to have a sensitivity of 27% and a specificity of 99.9%. The positive and negative predictive values were 98.5% and 79%, respectively. The test accuracy was 80%. Patients with a true-positive Gram stain had a significantly higher preoperative white blood-cell count, C-reactive protein level, and nucleated cell count in the aspirate when compared with patients with a false-negative Gram stain (p < 0.001). In no case did the results of the intraoperative Gram stain alter treatment.

Conclusions: The intraoperative Gram stain was found to have poor sensitivity and a poor negative predictive value, and its results did not alter the treatment of any patient undergoing revision total knee arthroplasty because of a suspected infection. These data do not support the routine use of intraoperative Gram staining in revision total knee arthroplasty; instead, they suggest a much more limited role for this test.

Level of Evidence: Diagnostic Level I. See Instructions to Authors for a complete description of levels of evidence.

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