The T4-L1-Hip Axis: Defining a Normal Sagittal Spinal Alignment

Jeffrey Hills, Lawrence G. Lenke, Zeeshan M. Sardar, Jean Charles Le Huec, Stephane Bourret, Kazuhiro Hasegawa, Hee Kit Wong, Hwee Weng Dennis Hey, Gabriel Liu, Hend Riahi, Mouna Chelli-Bouaziz, Michael P. Kelly

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Study Design. This is a cross-sectional cohort. Objective. The aim was to describe sagittal plane alignment and balance in a multinational cohort of nondegenerated, asymptomatic adults. Summary of Background Data. Current 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 Methods. Sagittal 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. Results. Among 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, r 2=0.3), but was strongly associated with the lumbar pelvic angles (L1PA, r 2=0.58). Defining lumbar lordosis as a function of PI and L1PA resulted in high explained variance (R 2=0.74) and the T4 pelvic angle had near perfect correlation with the L1PA (r=0.9). Conclusions. We 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.

Original languageEnglish (US)
Pages (from-to)1399-1406
Number of pages8
Issue number19
StatePublished - Oct 1 2022
Externally publishedYes


  • Adult deformity
  • Cone of economy
  • Lumbar lordosis
  • Lumbar pelvic angle
  • Pelvic incidence
  • Sagittal alignment

ASJC Scopus subject areas

  • Clinical Neurology
  • Orthopedics and Sports Medicine


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