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

PURPOSE: 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). METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Range of motion of thoracic spine in sagittal plane.

STUDY DESIGN: Imaging study of thoracic spine. OBJECTIVE: The purpose of this study was to investigate dynamic alignment and range of motion (ROM) at all segmental levels of thoracic spine. Thoracic spine is considered to have restricted ROM because of restriction by the rib cage. However, angular movements of thoracic spine can induce thoracic compressive myelopathy in some patients. Although few previous studies have reported segmental ROM with regard to sagittal plane, these were based on cadaver specimens. No study has reported normal functional ROM of thoracic spine. METHODS: Fifty patients with cervical or lumbar spinal disease but neither thoracic spinal disease nor compression fracture were enrolled prospectively in this study (34 males, 16 females; mean age 55.4 ± 14.7 years; range 27-81 years). After preoperative myelography, multidetector-row computed tomography scanning was performed at passive maximum flexion and extension position. Total and segmental thoracic kyphotic angles were measured and ROM calculated. RESULTS: Total kyphotic angle (T1/L1) was 40.2° ± 11.4° and 8.5° ± 12.8° in flexion and extension, respectively (P < 0.0001). The apex of the kyphotic angle was at T6/7 in flexion. Total ROM (T1/L1) was 31.7° ± 11.3°. Segmental ROM decreased from T1/2 to T4/5 but increased gradually from T4/5 to T12/L1. Maximum ROM was at T12/L1 (4.2° ± 2.1°) and minimum at T4/5 (0.9° ± 3.0°). CONCLUSIONS: Thoracic spine showed ROM in sagittal plane, despite being considered a stable region. These findings offer useful information in the diagnosis and selection of surgical intervention in thoracic spinal disease.