Evaluation of the serum level of CRP for diagnosing acute periprosthetic infection after TKA*

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Objective: To determine the serum level of C-reactive protein (CRP) with greater accuracy for diagnosing acute periprosthetic infection after total knee arthroplasty (TKA). Method: Case-control study evaluating serum levels of CRP after TKA in infected and uninfected groups. The serum levels of CRP were assessed in patients submitted to TKA who had been readmitted in the acute phase for surgical debridement with implant retention and had their diagnosis of periprosthetic infection confirmed. These values were compared with a control group, which did not present infectious complications. Results: Between March 2014 and March 2016, 1,373 TKAs were performed in the institution, and 28 patients (0.49%) were readmitted in the acute phase with a diagnosis of periprosthetic infection. Sixteen patients met the inclusion criteria. Gender, skin color, age, and body mass index (BMI) were similar between the groups. The patients in the acute periprosthetic infection group had significantly higher mean serum levels of CRP than the control group (p<0.001). For CRP levels = 30.615, the test's highest sensitivity (75%) and specificity (77%) were achieved, with an accuracy of 77.3% for the diagnosis of infection. The area under the 0.762 Receiver Operating Characteristics (ROC) curve showed satisfactory performance of the proposed test. Conclusion: Serum levels of CRP greater than 30.615 mg/L in the third week after TKA associated with clinical signs are highly suggestive of acute periprosthetic infection.Keywords: Knee; Osteoarthritis; Arthroplasty; Infection; CRP.*Study performed at the Centro de Cirurgia do Joelho, Instituto Nacional de Traumatologia e Ortopedia (INTO), Rio de Janeiro, RJ, Brazil.