Fig. 1

The illustrations of sagittal parameters including TK, LL, PT, PI and SS. As showed in left graph, TK (thoracic kyphosis) was measured as the cobb angle between the upper endplate of T4 vertebra and the lower endplate of T12 vertebra. TLJA (Thoracolumbar junctional angle) was the cobb angle between the upper endplate of T10 vertebra and the lower endplate of L2 vertebra. LL (lumbar lordosis) was the cobb angle between the upper endplate of L1 vertebra and the lower endplate of S1 vertebra. SS (sacrum slope) was the angle between the horizontal and the sacral plate. PT (pelvic tilt) was the angle between the vertical and the line through the midpoint of the sacral plate to femoral heads axis. PI (pelvic incidence) was measured as the angle subtended by a perpendicular from the upper endplate of S1 and a line connecting the center of the femoral head to the center of the upper endplate of S1. The right graph indicated the measurement of TK, LL, PT and PI by using Surgimap software