Cobb angle measurement for scoliosis

The Cobb angle (arrow in radiograph) is formed by the intersection of a line parallel to the superior end plate of the most cephalad vertebra in a particular curve, with the line parallel to the inferior end plate of the most caudad vertebra of the curve. The intersection of these lines may occur outside the border of the actual film. Therefore, by convention, perpendiculars to the parallels are drawn, and the angle between their intersection is measured. The Cobb angle in the above radiograph is 63°. The most cephalad end vertebra (E1) is the vertebra that has the greatest tilt from horizontal of its superior end plate (solid line). The most caudal end vertebra (E2) is the vertebra that has the greatest tilt from horizontal of its inferior end plate (dotted line). The apical vertebra (A) is the most laterally deviated vertebra from midline. Drawing lines along several vertebrae near each end of a curve (dashed lines) is helpful in determining that with the greatest tilt.