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Perioperative Testing for Joint Infection in Patients Undergoing Revision Total Hip Arthroplasty

¹ Castle Orthopaedics and Sports Medicine, S.C., 2111 Ogden Avenue, Aurora, IL 60504., E-mail address: mfs{at}castleortho.com
² Midwest Orthopaedics at Rush, Rush University Medical Center, 1725 West Harrison Street, Suite 1063, Chicago, IL 60612

Investigation performed at Midwest Orthopaedics at Rush, Rush University Medical Center, and Central DuPage Hospital, Chicago, Illinois

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 of less than $10,000 from Zimmer in the form of statistical analysis. In addition, one or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits or a commitment or agreement to provide such benefits from commercial entities in excess of $10,000 (Zimmer) and less than $10,000 (Stryker, Smith and Nephew). Also, a commercial entity (Zimmer) 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: Two hundred and thirty-five consecutive total hip arthroplasties in 220 patients were evaluated by one of two surgeons using a consistent algorithm to identify infection and were treated with reoperation. Receiver-operating-characteristic curve analysis was used to determine the optimal cut-point values for the white blood-cell count and the percentage of polymorphonuclear cells of intraoperatively aspirated hip synovial fluid. Sensitivity, specificity, negative predictive value, positive predictive value, and accuracy were determined. Patients were considered to have an infection if two of three criteria were met; the three criteria were a positive intraoperative culture, gross purulence at the time of reoperation, and positive histopathological findings.

Results: Thirty-four arthroplasties were excluded because of the presence of a draining sinus, incomplete data, or a preoperative diagnosis of inflammatory arthritis, leaving 201 total hip arthroplasties available for evaluation. Fifty-five hips were judged to be infected. No hip in a patient with a preoperative erythrocyte sedimentation rate of <30 mm/hr and a C-reactive protein level of <10 mg/dL was determined to be infected. Receiver-operating-characteristic curve analysis of the synovial fluid illustrated optimal cut-points to be >4200 white blood cells/mL for the white blood-cell count and >80% polymorphonuclear cells for the differential count. However, when combined with an elevated erythrocyte sedimentation rate and C-reactive protein level, the optimal cut-point for the synovial fluid cell count was >3000 white blood cells/mL, which yielded the highest combined sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the tests studied.

Discussion: A synovial fluid cell count of >3000 white blood cells/mL was the most predictive perioperative testing modality in our study for determining the presence of periprosthetic infection when combined with an elevated preoperative erythrocyte sedimentation rate and C-reactive protein level in patients undergoing revision total hip arthroplasty.

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

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				J. L. Del Pozo and R. Patel Infection Associated with Prosthetic Joints N. Engl. J. Med., August 20, 2009; 361(8): 787 - 794. [Full Text] [PDF]

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