STUDY DESIGN: Retrospective cohort study. OBJECTIVE: to compare muscle health and imaging markers in patients with 1-level L4-L5 stable versus unstable degenerative lumbar spondylolisthesis (DLS). SUMMARY OF BACKGROUND DATA: DLS may be stable or unstable. It is unknown how muscle health and other imaging markers are associated with DLS stability. METHODS: Patients≥18 years with 1-level L4-L5 DLS and preoperative flexion/extension radiographs were included. Normalized total psoas area (NTPA), body mass index (BMI)-normalized paralumbar (PL) (multifidus [MF]+erector spinae [ES]) cross-sectional area (PL-CSA/BMI), and Goutallier were assessed. Other L4-L5 markers included: facet orientation, slip percentage, pelvic incidence (PI), tilt (PT), sacral slope (SS), lumbar lordosis (LL), and PI-LL. Instability was defined as>
3 mm translation or>
10 degrees endplate change on flexion-extension. Low versus normal muscle health was defined as NTPA or PL-CSA/BMI below the lowest sex-specific quartile. Multivariate logistic regression was used to determine variables associated with instability. RESULTS: 251 patients (unstable=50
stable=201) were included. There were no significant differences in muscle health at L3, L4, or L5 or Goutallier on univariate analysis. The stable cohort had smaller slip percentage (19±9% vs. 15±8%, P=0.007) and PI-LL (13.56±12.75 vs. 5.81±14.46, P=0.002). The stable cohort had more patients with MF and ES total Goutallier≤2 (P=0.031, P=0.002, respectively) at L3-L4 versus L4-L5 and more patients with MF and ES total Goutallier≤2 (P=0.013, P=0.004, respectively) at L4-L5 versus L5-S1. On regression, low L4-L5 MF Goutallier was associated with instability (OR: 2.50, 95% CI [1.01 - 6.20], P=0.047). CONCLUSION: Patients with unstable L4-L5 spondylolisthesis have lower multifidus Goutallier at the slip level, greater slip percentage, and greater PI-LL mismatch. Patients with stable L4-L5 spondylolisthesis have greater Goutallier of the caudal paralumbars. LEVEL OF EVIDENCE: 3.