Daigo MoritaYasutsugu YukawaHiroaki NakashimaKeigo Ito • Go YoshidaMasaaki MachinoSyunsuke KanbaraToshiki Iwase •

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. Summary of background data 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.