Analysis of apex and transitional vertebra of the spine according to pelvic incidence using orientation and position parameters

Abstract

Objective: To identify the different apex and transitional vertebra according to the shape of the pelvis of individuals despite their difference in sagittal alignment using our measurement system. Methods: Full spine X-rays using EOS in standard stand-position of 99 volunteers were selected (47 women, 52 men, mean age 31years old). Validated 3D reconstruction technique allowing extraction of spinopelvic parameters, and position and rotation of each vertebra and lumbar discs. Subjects were divided in three groups: low PI (low PI, n=37), moderate PI (mid PI, n=52), high PI (high PI, n=10), with respectively a PI below 45 °, between 45 °-60 ° and above 60 °. Occurrence of specific position and rotation values of apex and transitional vertebra were assessed in each groups. Results: Frequency curves tend to move cranially when the incidence increases except in cervicothoracic where T1 is a constant for all shape of spine with occurrence approaching 90%. Angulation value of relevant vertebra and lumbar lordosis are significantly positively correlated for the whole population. Conclusions: Our study allowed the assessment of the distribution of spine curvatures according to the pelvic incidence. It describes the occurrence of localization of the apex and transitional vertebrae according to pelvic incidence. These results should be taken into account during the analysis of the sagittal balance, especially when planning deformity surgery in adults.