Can the supine extended position with legs straightened and a lumbar pillow complement the psoas-relaxed position for the diagnosis of lumbar spinal stenosis on MRI? A prospective cross-sectional study.

Introduction: When the diagnosis of lumbar spinal stenosis is uncertain in the conventional psoas-relaxed position (PRP) MRI, upright MRI is a not widely available alternative. The aim of this study was to investigate whether a modified supine MRI position with legs straight and an adjustable pillow under the lumbar spine (EXT) could mimic the effect of standing. Research question: We hypothesized that EXT would mimic upright MRI in stenosis severity. Materials and methods: Forty patients (58 % male, mean age 57 years) underwent a 3T (65 %) or 1.5T MRI. For the levels L2-S1, central stenosis (Lee: 0-3), dural cross sectional area (DCSA: mm Results: At L4/L5 EXT showed increased narrowing in 40 % (central), 37.5 % (lateral), and 17.5 % (foraminal). DCSA decreased (P < 0.0001) and LA increased (P < 0.0001), with strong correlations and high reliability (P < 0.0001). Lateral recess stenosis increased significantly in EXT at L4/L5 (P = 0.014; K = 0.646). No significant difference was observed in foraminal stenosis (K = 0.488). Discussion and conclusion: EXT increased lumbar lordosis to the normal standing range of approximately 50°, mimicking an upright MRI. A more realistic degree of central stenosis at all levels and of lateral recess stenosis at L4/L5 was shown. Foraminal stenosis did not increase.