Elevated postoperative C-reactive protein after primary hip and knee arthroplasty: kinetics and patient-related factors

Background Periprosthetic joint infection (PJI) is a rare but serious complication after hip and knee arthroplasty. The diagnostic value of preoperative and early postoperative C-reactive protein (CRP) remains controversial. This study characterized perioperative CRP kinetics following primary arthroplasty, with particular emphasis on CRP dynamics in patients without early PJI and patient-related factors associated with marked postoperative CRP elevation. Methods In this retrospective single-center study, 595 primary hip and knee arthroplasties performed in 546 patients with primary osteoarthritis were analyzed. Preoperative CRP and leukocyte counts were recorded. Postoperative CRP was assessed at days 1–3, 4–6, and 7–9. Early PJI (≤ 90 days) was defined according to the 2018 Musculoskeletal Infection Society (MSIS) criteria. CRP kinetics were primarily evaluated in infection-free patients, while CRP values in the small number of early PJI cases were reported descriptively. Subgroup analyses were performed based on data completeness and follow-up availability. Results Among procedures with ≥ 90-day follow-up, seven early PJI cases were identified. In infection-free patients, CRP levels peaked during postoperative days 1–3, with 49.8% exhibiting CRP values > 100 mg/L and subsequently declined over time. After multivariable adjustment, pre-existing renal insufficiency (OR 2.49; 95% CI 1.16–5.34; p = 0.020) and male sex (OR 1.74; 95% CI 1.06–2.85; p = 0.029) were independently associated with postoperative CRP > 100 mg/L during days 1–3. Owing to the small number of early PJI cases, PJI-related CRP data were considered descriptive only. Conclusions Marked early postoperative CRP elevations were common among patients without early PJI. Pre-existing renal insufficiency and male sex were independently associated with CRP values > 100 mg/L during postoperative days 1–3, highlighting substantial patient-related variability in the postoperative inflammatory response in patients without documented early PJI. These factors should be considered when interpreting early postoperative CRP values after primary arthroplasty. The small number of early PJI cases precluded assessment of the diagnostic performance of CRP for early PJI.