Imaging-Based Evaluation of Predictive Factors in Single- and Double-Level Isthmic Spondylolisthesis: A Comparative and Correlational Study

Objectives To compare sagittal alignment, disc degeneration, and paraspinal muscle status between patients with single-level L5 isthmic spondylolisthesis (L5-IS) and double-level isthmic spondylolisthesis (DLIS), and to evaluate predictive factors for DLIS. Methods Sagittal parameters including pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and lumbar lordosis (LL), as well as the cross-sectional areas of multifidus (MF CSA) and erector spinae (ES CSA), were measured. Comparative analysis, correlation analysis, and multivariate logistic regression were conducted. Results A total of 64 patients were included: 32 with DLIS and 32 with L5-IS. The DLIS group showed higher PI (60.56 ± 9.50 vs. 51.89 ± 9.70, P < 0.001) and PT (28.33 ± 9.31 vs. 20.91 ± 9.70, P = 0.03), but smaller MF-CSA (0.39 ± 0.12 vs. 0.49 ± 0.13, P = 0.002) and ES-CSA (0.82 ± 0.31 vs. 1.17 ± 0.38, P < 0.001). PI and PT were strongly correlated in both groups. Logistic regression identified increased PI (OR = 1.098), PT (OR = 2.090), and SS (OR = 2.014) as potential predictive factors. Receiver Operating Characteristic (ROC) curve analysis showed acceptable predictive performance for PI (AUC = 0.751) and PT (AUC = 0.711), while SS had limited value (AUC = 0.612). Conclusion DLIS patients exhibit greater pelvic parameters and paraspinal muscle atrophy. PI and PT may have predictive value for DLIS.