Relationship among cervical, thoracic, and lumbopelvic sagittal alignment in healthy adults

Purpose. To evaluate the association between cervical sagittal alignment and thoracic/lumbopelvic sagittal alignment in healthy Japanese adults. Methods. 30 male and 22 female healthy adults aged 22 to 50 years were recruited. Spinal parameters were measured on radiographs, including the cervical sagittal vertical axis, sagittal vertical axis, C7 tilt angle, Ishihara index for cervical lordosis, thoracic kyphosis, lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence. Results. The C7 tilt angle positively correlated with the Ishihara index (r=0.52, p<0.0001) and thoracic kyphosis (r=0.53, p<0.0001). The Ishihara index positively correlated with thoracic kyphosis (r=0.34, p=0.01) and C7 tilt angle (r=0.52, p<0.0001). Pelvic incidence positively correlated with sacral slope (r=0.45, p=0.001), lumbar lordosis (r=0.26, p=0.07), and pelvic tilt (r=0.29, p=0.03). Compared with men, women had a smaller Ishihara index (0.07 vs. 0.001, p=0.03), thoracic kyphosis (30.5 degrees vs 24.1 degrees, p=0.02), and C7 tilt angle (23.1 degrees vs. 16.8 degrees, p=0.02). Women had less cervical lordosis and thoracic kyphosis, that is, a straighter cervico-thoracic sagittal alignment. Conclusion. In healthy Japanese adults, cervical sagittal alignment is associated with thoracic sagittal alignment but not with lumbopelvic alignment.