The T4-L1-Hip Axis

Abstract

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.