Dynamic changes in the cross-sectional area of the dural sac and spinal cord in the thoracic spine.

Abstract

The thoracic spine is considered a rigid region because it is restricted by the rib cage. Previously, we reported functional alignments and range of motion (ROM) at all segmental levels. The purpose of this study was to investigate dynamic changes of the dural sac and spinal cord in the thoracic spine using a multidetector-row computed tomography (MDCT). Fifty patients with cervical or lumbar spinal disease were prospectively enrolled. After preoperative myelography, MDCT was performed at maximum passive flexion and extension. The anteroposterior diameter and cross-sectional area of the dural sac and spinal cord in the axial plane were measured using Scion imaging software. We also evaluated the correlation between the change ratio of the cross-sectional area and segmental kyphotic angle and ROM. In flexion, the anteroposterior diameter of the dural sac was larger than in extension. The cross-sectional area in the upper and middle regions was smaller, but was larger in the lower region. The anteroposterior diameter and cross-sectional area of the spinal cord in the upper and middle regions were smaller than in extension, but these values were nearly the same in both flexion and extension in the lower region. Change ratios of the cross-sectional area were correlated with segmental kyphotic angle rather than ROM. The thoracic spine showed some dynamic changes of the dural sac and spinal cord in the axial plane within functional motion. Segmental kyphotic angle, rather than segmental ROM, was the more important factor affecting dimensions of the dural sac and spinal cord.