A multidomain imaging comparison of single-level and double-level degenerative lumbar spondylolisthesis

Objective This cross-sectional retrospective study compared continuous double-level degenerative lumbar spondylolisthesis (dl-DLS) with isolated L4-5 single-level disease (sl-DLS) across three imaging domains: standing sagittal alignment, facet morphology, and paraspinal muscle morphology. Methods We reviewed 112 consecutively identified eligible patients from a single institutional imaging database (December 2024 to August 2025): 64 with isolated L4-5 sl-DLS and 48 with continuous L4/L5 dl-DLS. The groups were not matched and were classified solely by the involved slip levels; symptom severity and treatment choice did not determine group assignment. Standing whole-spine radiographs provided spinopelvic measurements, axial CT provided facet joint angle (FJA) and facet tropism (FT), and axial lumbar MRI provided multifidus (MF) and erector spinae (ES) cross-sectional area (CSA) and fatty infiltration (FI). Between-group testing and prespecified exploratory univariable analyses were performed. Results The groups did not differ in the measured baseline variables of age, sex distribution, or BMI. dl-DLS showed higher PI, PT, SS, SVA, and L1PA; these findings describe group differences in alignment and should not be interpreted as causal factors. At both L4-5 and L5-S1, dl-DLS showed smaller MF/ES CSA together with greater FI. Facet asymmetry was more evident in dl-DLS, with the largest difference observed for L5 FT. In exploratory univariable analyses, higher L4 FT and L5 FT and smaller MF and ES CSA at L4-5 were associated with dl-DLS; no predictive or causal inference was made. Conclusion In this selected cross-sectional cohort, continuous L4/L5 dl-DLS was associated with a multidomain imaging pattern comprising altered sagittal alignment, greater facet asymmetry, and poorer paraspinal muscle morphology. The findings define associative imaging characteristics rather than a distinct biological entity or a basis for treatment selection, and they require prospective validation.