Early post-operative CRP is a better predictor of DAIR failure than pre-operative CRP in total knee PJI

INTRODUCTION: Debridement, antibiotics and implant retention (DAIR) surgery is often performed as a first-line treatment for periprosthetic joint infection (PJI), however, success rates are variable. This study aimed to determine whether post-operative C-reactive protein (CRP) levels predict DAIR failure. MATERIALS AND METHODS: A multi-centre retrospective cohort study was performed over a 15-year period. All total knee arthroplasty (TKA) patients undergoing DAIR for first episode PJI were included. CRP was measured at admission and for 6 weeks post-operatively. Treatment success was defined as implant retention without the need for revision surgery or long-term suppressive antibiotics. Trends in CRP were compared between two groups: failed and successful DAIR. Receiver operating characteristic (ROC) curves were analysed. RESULTS: 189 DAIR procedures were included, of which 49% (92) failed and 51% (97) were successful. Mean follow-up was 7.5 years. Overall, CRP trended down following surgery. Mean CRP was significantly higher in the failed DAIR group at all time points. The greatest difference was at week one post-operatively (mean 76 vs. 101, P < 0.01). This remained significant when patients experiencing DAIR failure within 90 days were excluded (mean 76 vs. 107, P < 0.01). CRP was most accurate as a predictor of failure at week one post-operatively, with an area under the curve (AUC) of 0.71. Optimal balance of specificity and sensitivity was achieved with a CRP cutoff of 89. This yielded a sensitivity of 74% and specificity of 66%. CRP at week one post-operatively more accurately predicted DAIR failure than admission CRP. CONCLUSIONS: CRP measured at week one post-operatively demonstrated moderate prognostic value for predicting DAIR failure in the treatment of total knee PJI. While an elevated CRP may assist in identifying patients who require close monitoring, CRP alone is insufficient to guide decisions around revision surgery.