• Jeffrey Hills, Lawrence G Lenke, Zeeshan M Sardar, Jean-Charles Le Huec, Stephane Bourret, Kazuhiro Hasegawa, Hee-Kit Wong, HeyHwee Weng DennisHWDDepartment of Orthopedic Surgery, National University Hospital (Singapore), Singapore, Singapore., Gabriel Liu, Hend Riahi, Mouna Chelli-Bouaziz, and Michael P Kelly.
• University of Texas, San Antonio, TX.
• Spine. 2022 Oct 1; 47 (19): 1399-1406.

Study DesignThis is a cross-sectional cohort.ObjectiveThe aim was to describe sagittal plane alignment and balance in a multinational cohort of nondegenerated, asymptomatic adults.Summary Of Background DataCurrent sagittal alignment targets were developed using correlations between radiographic and quality-of-life measures in spinal deformity patients, rather than disease-free samples leading to relatively poor accounting for variance within a population.Materials And MethodsSagittal balance was defined using vertebral body tilt and spinopelvic alignment was defined as the vertebral pelvic angles from C2 to L5 (vertebral pelvic angle=vertebral tilt+pelvic tilt). Associations with pelvic incidence (PI) were assessed using linear regression. Multivariable linear regression was used to estimate a normal L1-S1 lordosis, adjusting for PI and the L1 pelvic angle (L1PA). Correlation between the L1 and T4 pelvic angles was assessed to define a normal thoracic alignment conditioned on lumbar alignment.ResultsAmong 320 volunteers from 4 continents, median age was 37% and 60% were female. C2 tilt was independent of PI with minimal variation. PI was inadequate for estimating a normal lumbar lordosis (L1-S1, r2 =0.3), but was strongly associated with the lumbar pelvic angles (L1PA, r2 =0.58). Defining lumbar lordosis as a function of PI and L1PA resulted in high explained variance ( R2 =0.74) and the T4 pelvic angle had near perfect correlation with the L1PA ( r =0.9).ConclusionsWe defined normal sagittal balance and spinopelvic alignment in a disease-free international volunteer cohort. Four parameters are either fixed or directly modifiable in surgery and can define a normal thoracic and lumbar alignment: the L1-S1 lordosis defined as a function of PI and the L1PA; and the T4 pelvic angle is nearly equivalent to the L1PA, aligning the T4-L1-hip axis.Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.

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