Background: Although pelvic incidence (PI) is a key morphologic parameter in assessing spinopelvic sagittal alignment, accurate measurements of PI become difficult in patients with severe hip dislocation or femoral head deformities. This study aimed to investigate the reliability of our novel morphologic parameters and the correlations with established sagittal spinopelvic parameters.Methods: One hundred healthy volunteers (25 male and 75 female), with an average age of 38.9 years, were

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... . Whole-body alignment in the standing position was measured using a slot-scanning X-ray imager. We measured the established spinopelvic sagittal parameters and two original parameters: 1) the sacral incidence to pubis (SIP), which is the value of the angle between the line perpendicular to the superior plate of the first sacral vertebra at its anterior edge and the line connecting this point to the upper edge of the pubic symphysis, and 2) the pelvic inclination angle (PIA).Results: Reliability analysis showed high intra- and inter-rater agreements in all the spinopelvic parameters, with ICCs > 0.9. The SIP and PIA demonstrated strong correlation with PI (R = 0.96) and pelvic tilt (PT) (R = 0.92), respectively. PI could be predicted according to the regression equation: PI = –9.92 + 0.905 * SIP (R = 0.9596, p < 0.0001). The ideal lumbar lordosis (LL) could be predicted using the following equation using PI and age: ideal LL = 32.33 + 0.623 * PI – 0.280 * age (R = 0.6033, p < 0.001) and using SIP and age: ideal LL = 24.29 + 0.609 * SIP – 0.309 * age (R = 0.6177, p < 0.001).Conclusion: Both SIP and PIA were reliable parameters for determining the morphology and orientation of the pelvis, respectively. Ideal LL was accurately predicted using the SIP with equal accuracy as the PI. Our findings will assist clinicians in the assessment of spinopelvic sagittal alignment, decision-making, and ultimately help improve patient quality of life.