Association of Preoperative Systemic Inflammatory Indices with Early Postoperative Pain and Function After Total Knee Arthroplasty: A Retrospective Cohort Study.

BACKGROUND

Early postoperative pain and impaired function remain common after total knee arthroplasty (TKA). This study evaluated whether associations with early pain and 6-week function were consistent across six related preoperative complete-blood-count-derived inflammatory indices.

METHODS

This retrospective single-center cohort study included 114 patients who underwent unilateral primary TKA. Neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), and aggregate index of systemic inflammation (AISI) were calculated from blood samples obtained within 48 hours before surgery. Primary outcomes were numeric rating scale (NRS) pain at 24 hours and Hospital for Special Surgery (HSS) score at 6 weeks. Each index was entered separately into covariate-adjusted models; sensitivity analyses additionally adjusted for ASA grade, C-reactive protein, or erythrocyte sedimentation rate.

RESULTS

Higher values of all six indices were associated with higher NRS-24 hour scores and lower 6-week HSS scores. NLR, SII, and SIRI were also associated with greater 72-hour opioid use. In the descriptive NLR comparison, the unadjusted between-group differences were 1.41 points for NRS-24-hour pain and 5.71 points for 6-week HSS. Sensitivity analyses for the primary outcomes were materially unchanged. Exploratory discrimination beyond the clinical base model was modest (highest AUC, 0.702 for the SII-extended model).

CONCLUSION

Higher preoperative CBC-derived inflammatory indices, particularly NLR, SII, and SIRI, were associated with greater early pain burden and lower 6-week function after TKA. They are exploratory adjunctive signals rather than validated stand-alone screening tests or substitutes for clinical judgment. The retrospective single-center design, modest sample, and short follow-up require prospective multicenter validation.