In scoliosis assessment, which vertebral endplates define the apex for Cobb angle measurement?

• A. The top endplate of the upper vertebra and bottom endplate of the lower vertebra at the curve apex.
• B. The first and last vertebra of the spine.
• C. The vertebrae around the thoracic region.
• D. The vertebrae with the greatest rotation.

Answer: (A)

Cobb angle measurement relies on the endplates of the vertebrae that bound the curve. Identify the end vertebrae at the ends of the scoliosis curve—the top end-vertebra and the bottom end-vertebra. Draw a line along the superior endplate of the upper end-vertebra and a line along the inferior endplate of the lower end-vertebra. Perpendiculars to these lines define the angle, which is the Cobb angle. These endplates provide the correct reference planes because they define the limits of the curvature, not the entire spine or vertebrae chosen by rotation alone.