Radiologic Factors Associated With the Dynamic Change of Dural Sac Diameter in Lumbar Spine: A Kinematic MRI Study

Study Design: This is a cross-sectional radiologic study. Objective: The purpose of this study was to assess radiologic features related to dynamic changes of dural sac diameter using kinematic magnetic resonance imaging. Summary of Background Data: It is well known that the cross-sectional area of the lumbar spinal canal decreases during movement from flexion to extension. However, the radiologic characteristics related to dynamic changes of the lumbar spinal canal have not been elucidated. Methods: A total of 453 consecutive patients with clinically symptomatic low back pain or radiculopathy were recruited to undergo lumbar kinematic magnetic resonance imaging. The study participants consisted of 271 males (60%) and 182 females (40%). The average age was 44.5±12.2 years old. We investigated the following measurements at each level from L3–L4 to L5–S1: dural sac diameter, ligamentum flavum thickness, disk bulge, disk degeneration, angular motion, translational motion, and posterior disk height. The odds ratios (ORs) for ≥2 mm change of dural sac diameter between flexion and extension were calculated. Results: The average dural sac diameter was 12.2 mm in neutral, 12.5 mm in flexion, and 11.7 mm in extension, with an average difference between flexion and extension of 0.83 mm. The OR of a ≥2 mm change in L5–S1 was 0.55 as compared with L3–L4. Significantly increased ORs were observed with ≥3 mm of ligamentum flavum in neutral (OR: 4.05), 3–3.9 and ≥4 mm of disk bulge in neutral (ORs: 1.62 and 1.81, respectively), grade IV and V disk degeneration (OR: 2.59 and 2.86, respectively), ≥8 degrees of angular motion (OR: 1.81), and ≥2 mm of posterior disk height change (OR: 1.84). Conclusions: Several radiologic characteristics related to the dynamic change of dural sac diameter have been demonstrated.