Define the Cobb angle and explain its use in scoliosis assessment.

• A. The Cobb angle is the angle between lines drawn along the superior endplate of the most tilted vertebra above the curve and the inferior endplate of the most tilted vertebra below the curve on a standing AP radiograph, used to quantify scoliosis severity and monitor progression.
• B. The Cobb angle is the angle between the spinous processes of the most tilted vertebrae.
• C. The Cobb angle is the angle between the anterior margins of the vertebral bodies in the curve.
• D. The Cobb angle is the angle between the pedicles on the AP view.

Answer: (A)

The Cobb angle is the standard way to quantify scoliosis on a standing AP spinal radiograph. Identify the end vertebrae—the topmost and bottommost vertebrae of the curve that are most tilted. Draw a line along the superior endplate of the upper end vertebra and another along the inferior endplate of the lower end vertebra. Extend these lines until they intersect; the angle at their intersection is the Cobb angle. This measurement provides a numeric value for curve severity and is used to monitor progression over time and guide treatment decisions. The other described methods would measure angles between parts of the vertebrae that are not used in this assessment—spinous processes, anterior margins, or pedicles—so they do not reflect the scoliosis curve in the same standardized way.