Differences in Male and Female Spino-Pelvic Alignment in Asymptomatic Young Adults A Three-Dimensional Analysis Using Upright Low-Dose Digital Biplanar X-rays

Study Design. A three-dimensional analysis of spino-pelvic alignment in 60 asymptomatic young adult males and females. Objectives. To analyze the differences in sagittal spino-pelvic alignment in a group of asymptomatic young adult males and females and describe gender specific reference values. Summary of Background Data. Several spinal disorders like idiopathic scoliosis and Scheuermann's disease have a well-known sex-related prevalence ratio. As spino-pelvic alignment plays an important role in spinal biomechanics, it is imperative to analyze possible differences between the male and female spino-pelvic alignment. Furthermore, in spinal fusion surgery, normal sagittal balance should be recreated as closely as possible. Methods. An innovative biplanar ultra low-dose radiographic technique was used to obtain three-dimensional reconstructions of the spine (T1-L5), sacrum, and pelvis in a freestanding position of 30 asymptomatic young male and 30 young female adults. Values were calculated for thoracic kyphosis (T4-T12), lumbar lordosis (L1-S1), total and regional lumbopelvic lordosis (PRT12, PRL2, PRL4, and PRL5), sagittal plumb line of T1, T4, and T9 (HAT1, HAT4, and HAT9), T1-L5 sagittal spinal inclination, T9 sagittal offset, and pelvic parameters (pelvic tilt, sacral slope, and pelvic incidence). In addition, vertebral inclination in the sagittal plane of each vertebra was measured. Differences in spinopelvic alignment between the sexes were analyzed. Results. The female spine was more dorsally inclined (11 vs. 8; P = 0.003). High thoracic and thoracolumbar vertebrae were more dorsally inclined in women than in men. Thoracic kyphosis, lumbar lordosis, regional lumbopelvic lordosis, sagittal plumb lines, T9 sagittal offset, and pelvic parameters were not statistically different between the sexes. Conclusion. These results indicate that the female spine is definitely different from the male spine. The spine as whole and individual vertebrae in certain regions of the normal spine is more backwardly inclined in females than in males. Based on our previous research this signifies that these spinal regions are subjected to different biomechanical loading conditions. These vertebral segments are possibly less rotationally stable in females than in males.