C2 Pelvic Angle as a Predictive Measure for Decompensated Spinopelvic Alignment and Its Impact on Health-Related Quality of Life.

Abstract

Retrospective cohort. To evaluate the C2 pelvic angle (C2PA) as a novel compensatory parameter integrating C2 (center of gravity) and pelvic morphology, and its association with physical function and health-related quality of life (HRQOL). The T4-L1-Hip axis concept was applied to assess individualized spinal alignment. Adult spinal deformity (ASD) impairs physical function and HRQOL in older adults. Pelvic retroversion compensates for spinal degeneration to maintain posture, but standardized evaluative indices linking pelvic parameters to outcomes remain limited. Cross-sectional analysis of 383 community-dwelling adults (mean age 64.1 ± 10.3 y). Whole-spine radiographs, physical function tests (Timed Up and Go, 10-meter walk), and SF-36 HRQOL scores were analyzed. C2PA mismatch (measured C2PA minus normative value [0.4 × pelvic incidence - 13]) and thoracolumbar decompensation (T4PA-L1PA ≥4°) were assessed. ROC analysis identified optimal C2PA mismatch thresholds; propensity score matching (age/sex/BMI) compared groups. C2PA mismatch correlated strongly with lumbar (r=0.668) and thoracolumbar (r=0.707) mismatches. A 13° C2PA mismatch threshold optimally identified decompensated thoracolumbar alignment (AUC=0.819). Participants with>13° C2PA mismatch demonstrated decreased physical function (Timed Up and Go: 6.4 vs. 5.8 seconds; 10-meter walk: 1.4 vs. 1.5 m/s) and lower SF-36 scores (physical functioning: 65.9 vs. 72.8; bodily pain: 63.1 vs. 70.8; physical component summary: 41.8 vs. 45.7). C2PA is a reliable indicator of decompensated spinopelvic alignment, with>13° mismatch (measured C2PA>0.4 × pelvic incidence) The C2PA threshold correlates with decreased physical function and lower HRQOL, providing a clinical benchmark for evaluating and managing patients with spinal alignment degeneration. 3.