Evolution of distributional alignment goals

Concepts regarding sagittal plane alignment in adult spinal deformity (ASD) surgery are evolving in the pursuit of individualized care with personalized targets. We have moved past simple targets of mismatch between lumbar lordosis and pelvic incidence, as these ignore the distribution, and the subsequent shape, of lumbar lordosis. Several classification systems and alignment strategies exist, with some proposing alignment to “normal” while others seek age-appropriate spinal alignment. While differences exist, the importance of the pelvic incidence as a fixed parameter from which one may build the spine is common to all theories. The purpose of this narrative review is to summarize the literature regarding the current concepts behind spinal alignment theories and the data supporting these theories.