Breaking Down Instability: The Associations Between Muscle Health, Facet Joint Morphology, Spinopelvic Alignment, and Stability Status in Degenerative Lumbar Spondylolisthesis

Retrospective cohort study. To compare muscle health and imaging markers in patients with 1-level L4-L5 stable versus unstable degenerative lumbar spondylolisthesis (DLS). DLS may be stable or unstable. It is unknown how muscle health and other imaging markers are associated with DLS stability. Patients 18 years or older 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° 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. Two hundred fifty-one 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 = 0.001). 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]. 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 III.