Importance of sagittal alignment in spinal deformity

To maintain proper function and an erect posture, the spine compensates by changing the amount of kyphosis or lordosis at each region. However, in the setting of severe spinal malalignment, the compensatory motion of the spine may be inadequate, and may lead to compensatory spinopelvic and postural changes, which increase energy for standing and ambulation. Sagittal alignment has been shown through numerous studies to affect patient reported outcome scores. The goals of sagittal alignment are SVA < 50 mm, PI -LL < 20°, with various other equations (PI − LL < 10°, PI + LL + TK ≤ 45°, LL = [(PI + TK)/2] + 10) described to optimize surgical outcomes following correction. This review will look at the importance of sagittal alignment, how to measure spinopelvic alignment parameters, contributing variables to spinal alignment, and the clinical importance when spinal malalignment causes imbalance.