In this study, we designed a backpack that can reduce the moment arm of backpack load by placing the center of gravity of the backpack close to the axis of the spine. In order to investigate the effect of sagittal spinal alignment compared with the general backpack, we conducted the study using radiological images. The participants in this study were 18 adults (8 males and 10 females). The subjects participated in the experiment without carrying the backpack, wearing the normal backpack, and wearing a backpack designed to reduce the load moment arm by placing the center of gravity close to the body. Spinal alignment parameters were measured and analyzed using 3D radiography measurement software based on radiographic images taken under three conditions. The overall angle of lumbar lordosis, upper arc, lower arc, difference between pelvic incidence and lumbar lordosis, lower cervical lordosis, and sagittal vertical axis were measured. In the case of wearing the backpack rather than without the backpack, there was a significant difference in the overall angle of lumbar lordosis, lower arc, lower cervical spine angle, difference between pelvic incidence and lumbar lordosis, and sagittal vertical axis. In the case of wearing the backpack with reduced moment arm, the overall angle and lower arc of lumbar lordosis were significantly increased compared to those with the normal backpack. The difference between pelvic incidence and lumbar lordosis was significantly decreased. The results showed that a normal backpack caused imbalance of sagittal spinal alignment, and the backpack reducing the load moment arm by placing the backpack’s center of gravity close to the vertebral joint played a positive role in reducing the change of lumbar alignment compared with the normal backpack.
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