The Alignment and Compensation (AC) Classification of High-Grade Spondylolisthesis

This novel biomechanical classification provides a reproducible framework to describe HGS without reliance on approximated parameters. By integrating SVA, LSA, IP, and LL Apex, it captures compensated and decompensated states of malalignment with direct therapeutic implications. The system demonstrated excellent reliability and may serve as a foundation for future surgical guidelines.