Cobbs angle

The Cobb angle is the most widely used measurement to quantify the magnitude of spinal deformities, especially scoliosis, on plain radiographs. 

Scoliosis is a lateral spinal curvature with a Cobb angle of >10° 4. The Cobb angle technique can also assess the degree of kyphosis or lordosis in the sagittal plane

Lines are then drawn along the endplates (or the pedicles if the endplates are not properly visualized ), and the angle between the two lines, where they intersect, is measured.

Reference 

Fritz Hefti. Pediatric Orthopedics in Practice. (2007) ISBN: 9783540699644.