1.Impact of car seat recline angle on global spinal alignment and seat belt positioning: a prospective observational study in Japan
Norihiro NISHIDA ; Tomohiro IZUMIYAMA ; Ryusuke ASAHI ; Hidenori SUZUKI ; Masahiro KOIKE ; Masahiro FUNABA ; Kazuhiro FUJIMOTO ; Yusuke ICHIHARA ; Yogesh KUMARAN ; Hiroshi HAMANO ; Shigeru SUGIMOTO ; Takashi SAKAI
Asian Spine Journal 2026;20(2):283-293
Methods:
Lateral radiographs were obtained from 100 healthy adults in standing and seated postures at 25°, 35°, and 45° recline angles. Spinal parameters (cervical lordosis, thoracic kyphosis, thoracolumbar kyphosis, lumbar lordosis, sacral slope, pelvic tilt, and T1 spinopelvic inclination) and seat belt metrics (X-value, Z-value, and lap belt angle) were measured. Multivariate regression was used to assess associations with sex, age, height, and body mass index (BMI).
Results:
Reclining reduced cervical/lumbar lordosis and sacral slope, while thoracic kyphosis and pelvic tilt increased. Higher BMI was associated with a cranially shifted and more horizontal lap belt. Taller individuals showed greater T1 spinopelvic inclination and pelvic parameters. Females exhibited more pronounced thoracic kyphosis and pelvic retroversion across reclining angles.
Conclusions
Car seat recline significantly alters spinal alignment and seat belt positioning, with changes influenced by age, height, and BMI. These findings support ergonomic improvements in seat design and may inform surgical planning for ASD.
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