The Cobb angle is the most widely adopted technique to quantify the magnitude of spinal deformities, especially in the case of scoliosis, on plain radiographs.
To measure the Cobb angle, one must first decide which vertebrae are the end-vertebrae of the curve deformity – the vertebra whose endplates are most tilted towards each other 4.
Lines are then drawn along the endplates, and the angle between the two lines, where they intersect, measured.
In cases where the curvature is not marked, then the lines will not intersect on the film/monitor, in which case a further two lines can be plotted, each at right angles to the previous lines 1,4.
Most PACS will have a dedicated angle tool to measure this without needing the lines to intersect or need to add the aforementioned lines at right angles.
A scoliosis is defined as a lateral spinal curvature with a Cobb angle of 10° or more 4.
History and etymology
The Cobb angle was first described in 1948 by Dr. John R Cobb.