Fig. 1

The measurement demonstration of C2-C7 lordosis, T1 slope and C2-C7 sagittal vertical axis distance (a), thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI, angle between the green and blue dotted lines) and pelvic tilt (PT, angle between the yellow and blue dotted lines) (b). Proximal junctional angle (PJA) is defined as the sagittal Cobb angle between the upper instrumented vertebrae (UIV) and the 2nd vertebrae above the UIV (c).