Method of measurement of various parameters of sagittal spinal alignment. Sagittal vertical axis (SVA) is horizontal distance from C7 plumb line to front corner of sacrum. Positive values indicate position anterior to sacrum; negative values are through or behind sacrum. β, Angle of sacral inclination, is angle subtended by tangent to posterior border of S1 and vertical axis. δ, Cobb angle between two vertebrae.