Fig. 1

Schematic illustration showing the methodology for measurement of radiographic parameters. T1 slope, the angle between a horizontal line and the upper end plate of T1. NT, the angle formed by a vertical line from the sternum tip and a line connecting the center of the T1 upper end plate and the upper end of the sternum. TIA, the angle formed by a perpendicular line off the T1 upper end plate and another line connecting the center of the T1 upper end plate and the upper point of the sternum. C2-7 SVA, the distance from the posterosuperior corner of C7 to a vertical line from the center of the C2 vertebra. Cranial tilt, angle between the vertical line from the upper end plate of T1 and a line from the center of the upper end plate of T1 to the C2 center. Cervical tilt, angle between the two lines originating from the center of the T1 upper end plate: the vertical line and the line from the center of upper end plate of T1 to the C2 center