Sagittal imbalance of the spine is associated with poor sitting posture among primary and secondary school students in China: A cross-sectional study

Abstract Background There's no definite answer as to how writing posture affects students' spine. This study attempted to compare the sagittal curvature of the spine between sitting and standing postures in adolescents. To reveal the variation rule of spinal sagittal curvature of students with learning posture, and to discover the key factors that may affect students' spinal health. Methods 1138 participants (male, 604; female, 534; age range, 6–18 y) from three schools in Tianjin, China, including 570 primary school students and 568 secondary school students. This study used SpineScan and PA200 Station Posture Assessment System to assess the sagittal curvature of the spine for three postures: sitting on a chair in an upright position, seated at a desk while reading/writing, and standing in a natural relaxed position. Analyze the difference of the spine angle of the three postures and the correlation between the sagittal plane angle of the spine and body posture. Results When some teenagers sat reading/writing, the sagittal angle of the spine markedly changed, with the lumbar lordosis angle significantly decreased (p < 0.05) and the thoracic kyphosis angle significantly increased (p < 0.05). These angles interact with each other and were positively correlated with the height of the teenager (R2 = 0.179; p < 0.05). By contrast, teenagers with lumbar lordosis and thoracic kyphosis angles within standard references ranges in a seated reading/writing posture also had good spine shape while standing. Conclusions Compared with standing posture, the angle of thoracic kyphosis gradually increases from upright sitting to reading/writing., Lumbar lordosis significantly decreasing or even disappearing, and the flexion of whole spine will increase the risk of spinal injury. Height is an important factor affecting the shape of students' sitting spine.