Sacrum1-pubic angle: a novel and alternative morphologic radiological parameter for assessing spinopelvic sagittal alignment in human adults.

Objective: Spinopelvic sagittal balance ensures efficient posture and minimizes energy expenditure by aligning the spine, pelvis, and lower extremities. Deviations can cause clinical issues like back pain and functional limitations. Key radiographic parameters, including pelvic tilt (PT), pelvic incidence (PI), sacral slope (SS), and lumbar lordosis (LL), are essential for evaluating spinal pathologies and planning surgeries. Accurate PI measurement is challenging in certain conditions, necessitating alternative parameters. This study aimed to introduce a new, easily measurable parameter and examine its reliability and correlation with established sagittal parameters.

Methods: This study analyzed 107 asymptomatic adult volunteers (57 males and 50 females), with an average age of 36.75 years. Whole-spine radiographs in the standing position were taken using EOS technology. The established spinopelvic sagittal parameters and a novel parameter, sacrum1-pubic angle (S1PA), were measured. The correlation coefficient of each parameter, the regression equation of PI using S1PA, and the regression equation of PTα using PTβ were obtained. The intraclass correlation coefficients (ICCs) was calculated to evaluate the measurement reliability.

Results: Morphologic (S1PA, PI) and positional parameters (PTα, PTβ, PTγ, SS, LL) showed no significant gender differences (p > 0.05). S1PA had strong correlations with PI (r = -0.883, p < 0.001) and other parameters. PTα demonstrated a strong correlation with PTβ (r = -0.929, p < 0.001). PI could be predicted according to the regression equation: PI = 71.672 - 4.537 × S1PA (R² = 0.779, p < 0.001). The PTα could be predicted using the following equation: PTα = 67.245 - 0.865 × PTβ (R² = 0.864, p < 0.001). Reliability analysis showed high intra- and inter-rater agreement in all the spinopelvic parameters.

Conclusion: The S1PA is a dependable parameter for evaluating the morphology and orientation of the pelvis. PI could be precisely predicted using the S1PA. These insights are valuable for clinicians, enhancing their ability to assess spinopelvic sagittal alignment accurately.