Cobb's Angle and Scoliosis

Definition: Cobb's angle is a measurement of the degree of side-to-side spinal curvature, commonly referred to as scoliosis. This measurement is taken by first finding the most affected vertebra in the curve, called the apical vertebra. The apical vertebra is the spinal bone that has the most rotation and displacement from its ideal alignment. It also has the least amount of tilt, as measured by the angle of the endplates (top and bottom edges of vertebral body).

To come up with a number for the Cobb's angle, the top and bottom vertebrae of the curve are identified. These bones have the most tilt, but the least amount of rotation and displacement. They are located above and below the apical vertebra, respectively.

On the x-ray, a line is drawn along the edge of the vertebrae and extended out. On the top bone, the line starts at the high side, is drawn along the top edge and slopes downward according to the angle of the vertebra. On the bottom vertebra, the line is drawn along the bottom edge and will slope in an upward direction. Perpendicular lines are then drawn from both lines so that they meet each other at the level of the apical vertebra identified in the first step.

Cobb's angle is found by measuring the angle of the two intersecting perpendicular lines. If the Cobb's angle for your scoliosis is 15 degrees or less, it's likely that all you will need are regular check-ups to see if the curve is progressing. If it is between 20 and 40 degrees, you will probably need a back brace. If it is over 40, your doctor will likely recommend surgery.

_Sources:

GREINER, K., MD, MPH Adolescent Idiopathic Scoliosis: Radiologic Decision-Making. American Family Physician. March 2002. Accessed March 20, 2009.
Cobbs Angle. E-radiography.net. Accessed March 20, 2009.
Scoliosis. Teens Health Kids Health website. Accessed March 20 2009.

Also Known As: Cobb's angle