Introduction: Femoral fracture surgery in elderly patients is frequently followed by substantial acute postoperative pain, which may be influenced not only by surgical trauma but also by systemic inflammatory and immune responses. Because the Systemic Immune-Inflammation Index may reflect this biological susceptibility, the present study aimed to pathologically assess its association with the severity of acute postoperative pain after femoral fracture surgery.

Material and methods: This descriptive cross-sectional study was conducted at Shahid Madani Hospital, Tabriz, on 93 elderly patients selected by convenience sampling, with sample size estimated using Cochran’s formula. Demographic, clinical, laboratory, surgical, and postoperative pain data were collected. The Systemic Immune-Inflammation Index was calculated from preoperative platelet, neutrophil, and lymphocyte counts, and its association with acute postoperative pain severity was statistically evaluated.

Results: Patients with severe postoperative pain had markedly higher preoperative SII than those with moderate or mild pain (1801.2±789.6 vs 1280.5±542.7 and 850.2±386.4; P<0.001), along with higher inflammatory markers, lower hemoglobin and albumin, longer operations, greater blood loss, more opioid use, delayed mobilization, and longer hospitalization (all P<0.05). SII correlated with pain intensity (highest 24-hour NRS: r=0.574, P<0.001) and independently predicted severe pain (OR=2.86, 95% CI 1.54-5.31), with good accuracy (AUC=0.812).

Conclusion: Preoperative SII appears to be a clinically useful biomarker for identifying patients at increased risk of severe acute postoperative pain. Its independent association with pain severity and acceptable diagnostic performance suggest that SII may support early perioperative risk stratification and help guide individualized analgesic planning, particularly in patients with an elevated inflammatory burden before surgery.