Comparing Spinopelvic Angles and Magnification on Supine MRI With Standing Radiographs in Lumbar Spinal Stenosis

Study Design: Radiologic cross-sectional study based on a prospective cohort study (level III). Objective: Investigate whether lumbar lordosis (LL) and sacral slope (SS) differ significantly on supine magnetic resonance imaging (MRI) versus standing radiographs in nondeformity lumbar spinal stenosis (LSS). Secondly, to quantify the amount of magnification on standing lumbar radiographs. Summary of Background Data: Supine MRI is routinely performed when diagnosing LSS. Standing radiographs are often supplemented to measure spinopelvic angles. Little research has been done on whether LL and SS translate from standing radiographs to supine MRI. Previous studies have trended to significant changes in LL and SS; however, none have been performed exclusively in nondeformity LSS. Materials and Methods: Review of preoperative standing lateral lumbar radiographs and midsagittal T2-weighted supine lumbar MRI in 211 patients with LSS without concomitant degenerative spondylolisthesis, measuring LL (L1–S1), segmental lumbar lordosis (sLL) (L4–S1) and SS, in addition to the anteroposterior diameter and height of the L3 vertebral body. We conducted a reliability study and performed a Pearson’s correlation analysis. Data was presented in Bland-Altman plots. Results: Interobserver reliability was good to excellent, with ICC ranging from 0.77 to 0.94 for all parameters. Statistically significant differences were observed in LL and SS between image modalities. The mean radiographic measurements were as follows: LL 48.9 (SD: 12.8), sLL 32.3 (SD: 8.1), and SS 37.3 (SD: 8.7) degrees. The mean MRI measurements were as follows: LL 46.0 (SD: 10.5), sLL 32.3 (SD: 7.1), and SS 38.1 (SD: 7.1) degrees. Mean vertebral body magnification was between 21% and 23% for L3 anteroposterior diameter and height. Conclusions: Our results suggest that supine lumbar MRI might be a viable alternative to standing lateral lumbar radiographs for measuring LL and SS in routine follow-up for patients with LSS without concomitant spinal deformity. Standing radiographs are recommended as part of the initial investigation for LSS. Standing lumbar radiographs may yield high grades of magnification.