LL: the angle between the upper end plates of L1 and S1; SL: the angle between the lower endplate of the vertebra above the surgical level and the upper endplate of the vertebra below the surgical level; TK: the angle between the upper endplate of T5 and the lower endplate of T12; C7-SVA: the distance between the C7 plumb line and the posterosuperior border of S1; PI: the angle between the vertical line of the sacral endplate and the line connecting the midpoint of the sacral endplate to the midpoint of a line connected the centers of the femoral heads; PT: the angle between the line connecting the midpoint of the sacral endplate and the midpoint of the bilateral femoral head center and the C7 plumb line; SS: the angle between the horizontal plane and the sacral plate; DH: an average value of the anterior disc height and posterior disc height