Timepoint-Specific Percentile Reference Curves for C-Reactive Protein and Erythrocyte Sedimentation Rate After Uncomplicated Primary Reverse Shoulder Arthroplasty: A Single-Center Cohort Study

Background/Objectives: No shoulder-specific percentile reference range exists for postoperative C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR) after reverse shoulder arthroplasty (RSA); clinicians rely on time-invariant thresholds borrowed from lower-extremity cohorts, and the ESR trajectory is uncharacterized. Methods: We retrospectively studied a single-surgeon registry of elective primary RSA (2018–2026); after predefined exclusions, 214 procedures (206 patients) remained, with no infection events by design. CRP and ESR were measured preoperatively and on postoperative days 2, 5, and 14 (exploratory days 1, 3, 7). We computed empirical 50th–95th percentile curves with bootstrap confidence intervals, supported by mixed-effects, quantile-regression, missingness, and within-patient fold-change analyses. Results: CRP peaked on day 2 (95th percentile 13.33 mg/dL); its day 14 95th percentile returned to, and lay numerically below, the preoperative 95th percentile (1.53 versus 2.34 mg/dL). ESR fell on day 2 (77.8% of procedures at or below their preoperative value), then rose and remained elevated at day 14 (95th percentile 56.00 mm/h); upper percentiles exceeded the 30 mm/h threshold at baseline and from day 3 onward. Conclusions: These curves describe an uncomplicated course rather than validated diagnostic thresholds; they provide a shoulder-specific normative reference and ESR trajectory for RSA, and a benchmark for future infection-event cohorts.