Diagnosing Infection in the Setting of Periprosthetic Fractures

Background: The diagnosis of periprosthetic joint infection is particularly challenging in patients with periprosthetic fractures. The purpose of this study was to investigate the utility of commonly used diagnostic tests for periprosthetic joint infection in patients with a periprosthetic fracture. Methods: Of 121 patients treated with a periprosthetic fracture (97 hips, 24 knees, mean age: 72.9), 14 (11.6%) met Musculoskeletal Infection Society criteria for infection. Diagnostic variables were evaluated using logistic regression models for the prediction of infection and receiver operating characteristics curves. Results: The synovial white blood cell (WBC) count and differential were the best diagnostic tests, with good test performance (area under the curve, 84%) and optimal cutoffs of 2707 WBC/uL and 77% polymorphonuclear cells. The erythrocyte sedimentation rate and C-reactive protein were found to have overall lower test performance but remained relatively sensitive at standard cutoff values of 30 mm/h and 10 mg/L, respectively. Conclusion: The synovial fluid WBC count and differential are the best tests with optimal cutoff values that are similar to those used for patients without a periprosthetic fracture. (c) 2016 Elsevier Inc. All rights reserved.