Flatback syndrome
Condition in which the lower spine loses some of its normal curvatures. It is a type of sagittal imbalance or front-to-back imbalance in the spine.
In most instances, sagittal imbalance is due to a shortfall of lumbar lordosis (LL) relative to the pelvic incidence (PI) (i.e. LL is more than 9° below PI), which is designated as flatback syndrome.