ABSTRACT
PURPOSE: To define possible mechanism of posture-dependent symptom of spinal stenosis by measuring the effect of low back motion on the morphologic change of intervertebral disc and spinal canal. MATERIALS AND METHODS: Twenty healthy young volunteers underwent magnetic resonance imaging (1.5T MR scanner, GE) while supine with their lumbar spine in neutral, flexed, extended, and right and left rotational positions. The axial MR images at the middle of the intervertebral disc of L3-4 and L4-5 were analyzed to measure the difference of the size and shape of the disc and spinal canal in each posture. RESULTS: Extension decreased the sagittal diameters and the cross-sectional areas of the dural sac and spinal canal and increased the thickness of ligamentum flavum, whereas flexion had the opposite effects. The gap between convex posterior disc margin and anterior margin of facet joint of each side, represented as subarticular sagittal diameter, increased with flexion and decreased with extension or rotation. The directions of the rotation did not result any asymmetry of the subarticular sagittal diameter, but right rotation resulted thickening of right ligamentum flavum. The shape and dimensions of disc did not significantly change according to the positions of low back. CONCLUSIONS: With extension or rotation, the thickness of ligamentum flavum increased and posterior margin of the intervertebral disc was approximated to facet joint secondary to posterior movement of upper vertebral body without any change of shape and size of the disc. These phenomena result decrease of the size of spinal canal and dural sac in extension or rotation posture in young healthy people and may explain the posture-dependent symptom of spinal stenosis.