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.

Methods: Male and female patients with computed tomography data were selected. Dimensions of the first thoracic (T1), fourth lumbar (L4), and fifth lumbar (L5) vertebrae were measured, and bone models consisting of the cancellous and cortical bones made from polyurethane foam were created. PS with diameters of 4.5 mm, 5.5 mm, and 6.5 mm were used. T1 PS were 25 mm long, and L4 and L5 PS were 40 mm long. The bone models were secured with cement, and the MIT was measured using a calibrated torque wrench. After MIT testing, the PS head was attached to the machine’s crosshead. POS was then calculated at a crosshead speed of 5 mm/min until failure. Results: The L4 and L5 were notably larger in female bone models, whereas the T1 vertebra was larger in male bone models. Consequently, the MIT and POS for L4 and L5 were higher in female bone models across all PS diameters than in male bone models. Conversely, the MIT for T1 was higher in male bone models across all PS; however, no significant differences were observed in the POS values for T1 between sexes. Conclusions The mechanical properties of the proposed bone models can vary based on the vertebral structure and size. For accurate 3D surgical and mechanical simulations in the creation of custom-made medical devices, bone models must be constructed from patientspecific medical images.