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The Cobb angle is used to quantify the magnitude of spinal deformities, especially in the case of scoliosis.
To measure the Cobb angle, one must first decide which vertebrae are the end-vertebrae of the curve deformity (vertebrae at the upper and lower limits of the curve) and then Cobb angle formed by the intersection of the two lines.
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.
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.
History and etymology
The Cobb angle was first described in 1948 by Dr. John R Cobb.