Comparative Performance of the ESSG-ADSCI and ISSG-SII in a Single-center Adult Spinal Deformity Database

Introduction: In 2018, the ESSG and ISSG introduced their respective surgical complexity indices—the "Adult Deformity Surgery Complexity Index" (ESSG-ADSCI) and the "Surgical Invasiveness Index" (ISSG-SII). However, their performance has not been thoroughly evaluated or directly compared in the literature.

Methods: 899 consecutive ASD patients were reviewed. This retrospective, single-center study included ASD patients with complete baseline and 1-year follow-up data. Patients meeting the inclusion criteria were analyzed to compare the predictive performance of ESSG-ADSCI and ISSG-SII. The primary outcomes assessed were EBL, operative time, and LOS. Secondary outcomes included the occurrence of surgical, medical, and intraoperative complications. ROC curves and AUC analysis were performed. A sub-analysis of patients treated before 2017, aligning with the development of the ESSG-ADSCI and ISSG-SII, was performed to evaluate the consistency of these findings across different time periods. All statistical analyses were performed with significance set at p< 0.05.

Results: 693 patients (age: 60.5 years; 77% female; BMI: 27.4 kg/m²) met the inclusion criteria. The ISSG-SII (mean: 90.0±38.1) and ESSG-ADSCI (mean: 19.3±7.5) were found to be a significant independent predictor of LOS, operative time, and EBL (p < 0.001). The ISSG-SII outperformed the ESSG-ADSCI in predicting overall surgical complications (AUC: 0.645 vs. 0.597, p=0.018), EBL greater than 1500 mL (AUC: 0.687 vs. 0.604, p < 0.001), and surgery duration over 240 minutes (AUC: 0.705 vs. 0.658, p=0.036). However, there was no significant difference between the indices in predicting LOS beyond seven days (AUC:0.687 vs. 0.654, p=0.103). A sub-analysis of patients treated before 2017 reveals comparable outcomes, reinforcing the consistency of these findings across different time periods.

Conclusion : Both the ESSG-ADSCI and ISSG-SII demonstrate independent predictive value for key surgical outcomes, including length of stay, operative time, and blood loss in ASD surgery. However, the ISSG-SII consistently outperforms the ESSG-ADSCI in predicting surgical complications, excessive blood loss, and prolonged operative time. These findings highlight the utility of both indices in assessing surgical complexity, with the ISSG-SII showing greater sensitivity in identifying high-risk cases.