Analysis of the Sagittal Balance of the Spine and Pelvis Using Shape and Orientation Parameters

TLDR

Understanding normal sagittal relationships is essential for interpreting spinal and pelvic balance in health and disease. This study introduces a method to analyze global sagittal balance of the trunk using shape and orientation indices of the pelvis and spine. Standing lateral x‑rays of 160 asymptomatic young adults were modeled with dedicated software to calculate pelvic incidence, pelvic tilt, sacral slope, and cervical, thoracic, and lumbar curvature and tilt. Significant linear correlations were found between adjacent shape and orientation parameters across all spinal levels, strongest at the pelvis, lumbar, and cervical regions and weaker at the thoracic level, confirming that the spine and pelvis form a linear chain where changes at one level directly influence adjacent segments.

Abstract

Objective: The purpose of this study is to introduce a method to analyze and characterize the global sagittal balance of the human trunk using indexes derived from the shape and orientation of the pelvis and cervical, thoracic, and lumbar spine. Methods: Standing lateral x-rays of a cohort of 160 asymptomatic young adult volunteers were obtained. On each radiograph, a simplified model of the spine and pelvis was created using a dedicated computer software, and the following shape and orientation variables were calculated at each anatomic level: pelvic incidence, pelvic tilt, sacral slope, cervical curvature and tilt, thoracic curvature and tilt, and lumbar curvature and tilt. Results: Significant linear correlations were found between each single adjacent shape parameter as well as between each single adjacent orientation parameter at all anatomic levels. Significant correlations were also found between some shape and orientation parameters at the same anatomic level as well as between adjacent anatomic areas. In general, the linear correlations were stronger between shape and orientation variables at the pelvic, lumbar, and cervical areas and weaker at the thoracic level and between the thoracic and lumbar areas. Conclusions: These results confirm that the pelvis and spine in the sagittal plane can be considered as a linear chain linking the head to the pelvis where the shape and orientation of each anatomic segment are closely related and influence the adjacent segment to maintain a stable posture with a minimum of energy expenditure. Changes in shape or orientation at one level will have a direct influence on the adjacent segment. Knowledge of these normal relationships is of prime importance for the comprehension of sagittal balance in normal and pathologic conditions of the spine and pelvis.