Level-Specific Differences in Degenerative Spondylolisthesis: A Comparative Analysis of L3 versus L4 Spinopelvic Alignment, Facet Joint Morphology, and Muscle Degeneration Patterns.

Abstract

To investigate the distinct biomechanical characteristics of L3 versus L4 degenerative spondylolisthesis (DS) by comparing spinopelvic sagittal parameters, facet joint morphology, and paraspinal muscle degeneration patterns. This retrospective comparative cohort study included 112 patients who underwent surgical treatment for single-level DS (48 L3-L4, 64 L4-L5) between 2021 and 2023. Comprehensive radiographic analysis assessed spinopelvic sagittal alignment parameters using full-spine standing radiographs. Facet joint angles and pedicle-facet angles were measured using computed tomography. Paraspinal muscle cross-sectional area and fat infiltration were quantified using magnetic resonance imaging at multiple lumbar levels. L4DS patients demonstrated significantly greater global sagittal imbalance compared to L3DS patients (sagittal vertical axis: 3.43 ± 3.99 mm vs. 0.13 ± 3.86 mm, P < 0.01). L3DS patients exhibited larger facet joint angles at L4-L5 and L5-S1 levels, suggesting protective compensatory adaptations. L4DS patients showed more severe vertebral slippage (19.02 ± 7.47% vs. 15.85 ± 7.09%, P < 0.05) and greater multifidus fat infiltration at the L3-L4 level (40.36 ± 14.06% vs. 30.42 ± 13.31%, P < 0.05). Muscle cross-sectional areas remained comparable between groups. L3 and L4 DS represent distinct pathological entities with fundamentally different compensatory mechanisms, morphological adaptations, and degenerative patterns. These level-specific differences may have important implications for surgical planning and treatment strategies.