Early Postoperative Inflammatory Responses Following Primary Total Hip Arthroplasty Using Different Antibiotic-Loaded Bone Cement Formulations: A Prospective Observational Cohort Study.

Introduction: Periprosthetic joint infection (PJI) remains one of the most challenging complications following total hip arthroplasty (THA). Antibiotic-loaded bone cement (ALBC) provides high local antibiotic concentrations and is widely used in patients at increased risk of infection. Although several dual-antibiotic formulations have been investigated, their influence on the early postoperative inflammatory response has not been directly compared. Methods: In this prospective observational cohort study, 35 patients undergoing primary cemented THA between January 2025 and January 2026 were allocated to one of five ALBC regimens according to routine clinical practice: gentamicin alone, gentamicin-vancomycin, gentamicin-clindamycin, gentamicin-meropenem, or gentamicin-tobramycin (n = 7 per group). Serum C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and leukocyte count were measured preoperatively and on postoperative Days 1, 3, and 7. Longitudinal analyses accounting for within-patient correlations were performed to assess the effects of treatment group, postoperative time, and the group × time interaction. Day-specific between-group comparisons using one-way analysis of variance (ANOVA), with eta-squared (η2) as an effect-size measure, were performed as secondary analyses, with Bonferroni adjustment applied to post-hoc pairwise comparisons. Results: All treatment groups demonstrated progressive reductions in postoperative inflammatory markers. Longitudinal analysis demonstrated significant effects of treatment group, postoperative time, and the group × time interaction for CRP and ESR (all p < 0.001). For leukocyte count, significant effects of time and the group × time interaction were observed (both p < 0.001), whereas the overall group effect was not statistically significant (p = 0.071). Secondary day-specific analyses showed significant between-group differences in CRP, with comparatively lower values observed in the gentamicin-meropenem group. Several pairwise differences in CRP and ESR remained statistically significant after Bonferroni adjustment, whereas no pairwise differences in leukocyte counts remained significant after correction. Conclusions: Different antibiotic-loaded PMMA formulations were associated with distinct early postoperative inflammatory profiles. Gentamicin-meropenem was associated with comparatively lower CRP and ESR values; however, these exploratory findings do not establish superior infection-preventive efficacy and require confirmation in larger studies.