Different Degeneration Patterns of Paraspinal Muscles Between Double-Level and Single-Level Lumbar Spondylolisthesis: An Magnetic Resonance Imaging Analysis of 140 Patients.

Objective: To evaluate the degeneration patterns of paraspinal muscles in double-level degenerative lumbar spondylolisthesis (dl-DLS) versus single-level degenerative lumbar spondylolisthesis (sl-DLS).

Methods: A total of 67 dl-DLS and 73 sl-DLS patients were included. Multifidus (MF), erector spinae (ES), and psoas major (PM)'s fatty infiltration (FI) and relative cross-sectional area (rCSA) were measured. Sagittal parameters such as lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS) were also assessed. Comparisons and correlation analysis were performed between the 2 groups.

Results: MF atrophy is worse in dl-DLS patients from L3-4 to L5-S1, with higher FI from L1-2 to L5-S1 compared to sl-DLS patients. ES atrophy and FI are more pronounced in dl-DLS patients from L1-2 to L5-S1. PM atrophy is more significant in dl-DLS patients at L2-3 to L5-S1, with heavier FI from L1-2 to L3-4, though no difference in FI from L4-5 to L5-S1. The rCSA and FI of MF and ES show significant differences between adjacent segments in both groups, except for MF rCSA between L3-4 and L4-5 in dl-DLS. In dl-DLS, PM rCSA negatively correlates with PT from L4-5 to L2-3, while FI of MF and ES in L5-S1 positively correlates with LL. In sl-DLS, PM FI in L4-5 and L5-S1 negatively correlates with LL.

Conclusion: Degeneration of MF, ES, and PM is more severe in dl-DLS patients, particularly at the spondylolisthesis level. Severe paraspinal muscle degeneration can lead to spinal force imbalance and progression from sl-DLS to dl-DLS. The degradation of PM and ES correlates negatively with PT and SVA, indicating a link to pelvic decompensation and SVA abnormalities, potentially causing disproportionate degenerative changes in dl-DLS patients.