Elevation of fibrin degradation product (FDP) values prevents the negative conversion of serum CRP values after total knee arthroplasty

Background: It is essential as an orthopedic surgeon to diagnose prosthetic joint infection (PJI) at an early stage and to carry out precise treatment as well as preventing the deterioration of functional prognosis as much as possible. We suspected that PJI might have been caused because the negative conversion of creatinine reactive protein (CRP) has been prolonged after total knee arthroplasty (TKA) and patients with no serum CRP negative conversion have been treated with antibiotics to avoid the morbidity of PJI. The purpose of the present study is to investigate the factors associated with prolongation of the negative conversion of CRP, with the exclusion of PJI patients. Methods: We performed a retrospective case control study at our institution from August 2014 to August 2016. We classified the patients into two groups based on whether it required >= 20 days (Group A, n = 23) or < 20 days (Group B, n = 23) for CRP levels to normalize. Serum D-Dimer and fibrin degradation product (FDP) values were measured at 1, 2, 5, 9, 12, 16, 19, 23, 26, and 30 days after TKA. Exclusion criteria include anticoagulant oral administration cases before TKA, venous thromboembolism (VTE) by postoperative lower limb venous echocardiography before and after TKA, CRP re-elevation cases, and patients with PJI. The cutoff points for D-dimer and FDP levels for screening tests were calculated from the receiver operating characteristic (ROC) curve. Results: The ROC analysis of D-Dimer values at 30 days after TKA yielded an AUC of 0.891 (95% confidence interval (CI) 0.858-1.000), which indicates nearly an excellent test. The cutoff point of 22.1 mu g/dl for FDP value (Younden Index: 22.1 mu g/dl) showed a sensitivity of 81.8% (95% CI 70.1-92.8) and a specificity of 80.0% (95% CI 67.9-89.1) Conclusion: We revealed that CRP values of patient with an FDP level >= 22.1 mu g/dl at 30 days after TKA necessarily showed negative conversion without antibiotic administration, when examining a patient with elevated serum CRP of minor criteria in the definition of PJI proposed by MSIS (other criteria do not apply).