Abstract
Background
Flexion-extension radiographs are commonly used to assess lumbar instability in degenerative spondylolisthesis, but may underestimate mobility due to limited motion and muscle guarding. This study compared position-dependent translation and instability classification on (1) standing flexion-extension radiographs and (2) standing neutral-to-horizontal computed tomography (CT)/magnetic resonance imaging (MRI), and evaluated associations with postoperative patient-reported outcome measures (PROMS) change.Methods
In this retrospective single-center cohort study, surgically treated lumbar spinal stenosis patients with degenerative spondylolisthesis were assessed with standing neutral, standing flexion and extension radiographs, and horizontal CT and/or MRI within 6 months preoperatively (n = 227). Outcome measures were translation (millimeters [mm]), instability (Δ translation ≥4 mm), numeric rating scale (NRS) back/leg pain, and Oswestry Disability Index. Translation was measured on each modality. We compared mean translation change for flexion-extension and for standing neutral-to-horizontal CT/MRI. Correlation and agreement (overall agreement; Cohen's κ) were calculated. PROMS change was analyzed with regression adjusting for surgical technique.Results
Mean translation change was smaller on flexion-extension radiographs (1.4 ± 2.1 mm) than on standing neutral-to-horizontal comparisons (2.7 ± 2.6 mm for CT and 2.7 ± 2.3 mm for MRI; p Conclusions
Standing neutral-to-horizontal comparisons show larger position-dependent translation and often reclassify instability compared with flexion-extension radiographs. When horizontal CT/MRI is available, routine flexion-extension radiographs may add limited incremental information; standing extension radiographs may be a practical alternative when advanced imaging is unavailable. Imaging-defined instability was not consistently associated with midterm PROMS improvement.