Evaluating Variations in Spinopelvic Parameters from Sitting to Standing: A Comparative Analysis of 1447 Older Adults Across Age, BMI, and Gender Subgroups

<b>Background/Objectives</b>: Sagittal spinal alignment goals for adult spinal deformity (ASD) surgery are predominantly derived from standing radiographs, despite the biomechanical relevance of sitting posture. Existing studies on sitting alignment involve young, healthy cohorts, which poorly represent ASD patients. This study assessed posture-dependent changes in spinopelvic parameters, including pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and lumbar lordosis (LL), and examined how age, BMI, and gender influence these changes. <b>Methods:</b> In this retrospective cohort study, sitting and standing lateral radiographs of 1447 patients were evaluated. Spinopelvic parameters were measured, and changes (ΔPI, ΔPT, ΔSS, and ΔLL) were calculated. Multiple regression analysis was used to determine associations between these changes and age, BMI, and gender. <b>Results</b>: All parameters differed significantly between positions (<i>p</i> < 0.001); PT and PI increased in sitting (ΔPT = -19.20°; ΔPI = -4.52°), while SS and LL increased in standing (ΔSS = 14.67°; ΔLL = 18.44°). Older age correlated with increased ΔPT (<i>p</i> < 0.001) and ΔPI (<i>p</i> = 0.049) but reduced ΔLL and ΔSS (<i>p</i> < 0.001). Higher BMI was associated with decreased ΔPI, ΔPT, and ΔLL (<i>p</i> < 0.001, 0.003, and 0.025). Females showed greater ΔPT (<i>p</i> = 0.013) but smaller ΔPI, ΔSS, and ΔLL (<i>p</i> = 0.043, <0.001, and 0.001). <b>Conclusions</b>: Spinopelvic parameters vary significantly between sitting and standing positions, affected by age, BMI, and gender. The observed PI change suggests SIJ involvement, highlighting the need for posture-specific and demographic-adjusted alignment goals in ASD surgery to optimize outcomes.