Normative Values for Spinopelvic Sagittal Parameters in the Asymptomatic Indian Population

Background Accurate assessment of sagittal spinal and spinopelvic alignment is critical for evaluating adult spinal deformity (ASD) and optimizing surgical outcomes. However, most existing normative data and planning formulas are derived from Western populations, with limited data available from older Indian adults. This study aims to define normative values of sagittal alignment and spinopelvic parameters in asymptomatic Indian adults over 50 years of age and to develop population-specific regression models for preoperative planning in spinal deformity correction. Methods A prospective observational study was conducted on 250 asymptomatic Indian adults aged over 50 years (164 men, 86 women; mean age 59.95 ± 7.78 years). Standing whole-spine lateral radiographs were used to measure sagittal spinal and spinopelvic parameters. Pearson's correlation and regression analyses were performed to identify inter-parameter relationships and derive prediction equations. Results The mean values were: pelvic incidence (PI), 50.95° ± 11.72, pelvic tilt (PT), 13.0° ± 7.12, sacral slope (SS), 38.11° ± 9.71, lumbar lordosis (LL), 54.9° ± 13.7, thoracic kyphosis (TK), 29.96° ± 9.66, cervical lordosis (CL), -10.79° ± 11.99, and sagittal vertical axis (SVA), -0.26 mm ± 32.16. The following regression equations were derived: LL = 0.687 × PI + 19.9, PT = 0.326 × PI - 3.617, SS = 0.633 × PI + 5.854. A significant negative correlation was found between TK and LL (r = -0.268, p < 0.01), while a weak, non-significant correlation was observed between CL and LL. A PI-LL mismatch >9° was present in 44% of participants, and 10.8% had sagittal imbalance (SVA >50 mm). Cervical morphology was straight in 49.6%, lordotic in 26%, sigmoid in 19.6%, and kyphotic in 4.8% of subjects. Conclusion This study establishes normative values and population-specific planning formulas for sagittal and spinopelvic parameters in Indian adults aged 50 years and above. These equations offer more tailored targets for deformity correction than generalized Western models, particularly in individuals with extreme PI values. Adopting individualized alignment goals may enhance surgical planning and improve outcomes in ASD.