Exploratory Analysis of Postoperative CRP Trajectories and Treatment Outcomes After Two-Stage Revision for Periprosthetic Joint Infection

Background: Determining infection eradication before reimplantation remains challenging during two-stage revision for chronic periprosthetic joint infections (PJI). This exploratory study investigated the association between serial postoperative C-reactive protein (CRP) trajectories and treatment outcome following prosthesis explantation during two-stage revision for chronic periprosthetic joint infection (PJI). Methods: We retrospectively reviewed patients undergoing two-stage revision for chronic hip or knee PJI between January 2020 and August 2024. Patients with weekly CRP measurements and at least 12 months of follow-up were included. Treatment failure was defined according to modified Delphi criteria. Weekly CRP concentrations and percentage changes from postoperative Week 1 (ΔCRP) were compared between groups. ROC analysis assessed CRP discrimination weekly. Results: Ninety-one patients were included; 50 (54.9%) achieved infection eradication and 41 (45.1%) experienced treatment failure. CRP increased during the first post-operative week in both groups. Week 1 CRP concentrations were not significantly different between groups (5.24 vs. 6.79 mg/dL, p = 0.108). From Week 2 onwards, postoperative CRP trajectories and relative reductions from Week 1 differed between patients with treatment success and those experiencing treatment failure. From Week 2 onward, CRP remained significantly higher in patients with treatment failure (Week 2: 3.91 vs. 2.27 mg/dL, p = 0.0017; Week 4: 3.28 vs. 0.94 mg/dL, p < 0.0001; Week 6: 2.16 vs. 0.70 mg/dL, p = 0.0007). Relative CRP reduction was significantly higher in the success group from Week 2 onward. Discriminatory performance improved over time, with AUCs of 0.699–0.782 at Weeks 2–6. Conclusions: In this exploratory cohort, postoperative CRP trajectories differed according to treatment outcome. A slower decline in CRP was associated with treatment failure, but these findings do not establish an independent prognostic effect. CRP should not determine reimplantation timing in isolation, but an unfavourable trajectory should prompt reassessment and consideration of repeat debridement and spacer exchange. Larger prospective multicentre studies are needed to confirm these associations and determine their clinical utility.