Background: The Systemic Immune-Inflammation Index (SII) has emerged as a reliable marker of systemic inflammation and has been associated with various postoperative outcomes in surgical patients. However, its relationship with acute postoperative pain in patients undergoing hip arthroplasty for femoral fractures remains underexplored. Objective: This study aims to investigate the correlation between the SII and acute pain intensity in patients undergoing hip arthroplasty for femoral fractures, along with its association with postoperative clinical outcomes such as length of hospital stay (LOHS), ICU admission, and platelet count.

Methods: This prospective observational study was conducted with 112 patients who underwent hip arthroplasty for femoral fractures. Preoperative blood samples were used to calculate the SII, and pain intensity was measured at various time points postoperatively using a visual analog scale (VAS). Clinical outcomes, including LOHS, ICU admissions, and platelet counts, were recorded.

Results: A significant positive correlation was found between the SII and postoperative pain intensity, with higher SII values associated with increased pain levels at 2 and 4 hours postoperatively (r = +0.745, p = 0.005). Additionally, patients with elevated SII values had significantly longer hospital stays (22 days vs. 17 days, p = 0.006), higher ICU admission rates (27.94% vs. 16.60%, p = 0.036), and elevated platelet counts. The SII was also significantly correlated with neutrophil and lymphocyte counts, highlighting its role in reflecting the inflammatory response.

Conclusion: The SII appears to be a promising predictor of postoperative pain intensity and adverse clinical outcomes in patients undergoing hip arthroplasty for femoral fractures. Elevated SII values are associated with increased pain, prolonged hospital stays, and higher rates of ICU admission. These findings suggest that the SII could serve as a useful biomarker for assessing postoperative complications and guiding clinical management in surgical patients.