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Cobb Diagnostic Test

The Cobb method is used to measure the amount of curvature in the spine. Lines are drawn parallel to the end plates of the vertebral bodies at the beginning and the end of the curve. A second line is drawn perpendicular to each of the first lines, and the angle between these two lines is equal to the Cobb measurement.

It is important to realize that the Cobb measurement is never exactly the same each time the spine is x-rayed since the measurement is affected by the position of the patient, the way the x-ray is taken, and the way the lines are drawn. As a result, there is a standard measurement error of 3 to 5 degrees. Therefore, major treatment decisions should not be made upon single measurements and small changes.

This is an example of a right thoracic curve in a 14-year-old female measuring 47 degrees by the Cobb Method.

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  • Published: July 11, 2002
  • Updated: July 22, 2008