CobbWinkel

The Cobb angle, also known as Cobb-Winkel in German, is the standard radiographic measure used to quantify scoliosis. It assesses the extent of spinal curvature in the coronal plane on a standing anteroposterior radiograph. The method is named after John R. Cobb, who described it in 1948.

To measure the Cobb angle, identify the uppermost vertebra that is most tilted toward the convex side (the upper end vertebra) and the lowermost vertebra that is most tilted toward the opposite convex side (the lower end vertebra). Draw a line along the superior endplate of the upper vertebra and a line along the inferior endplate of the lower vertebra. Construct lines perpendicular to these endplate lines; the angle where the perpendiculars intersect is the Cobb angle. If the lines do not intersect within the image, the angle is still determined by the standard method, with care taken to measure the appropriate angle.

Interpretation of the Cobb angle is central to clinical decision-making. A Cobb angle of 10 degrees or more on a standing radiograph is commonly used to define scoliosis. Severity is often categorized as mild (<25°), moderate (25–40°), or severe (>40°), but treatment decisions also consider patient age, growth potential, and progression rate. Serial measurements track changes over time to assess progression or response to treatment such as bracing or surgery.

Reliability and limitations include inter- and intra-observer variability and sensitivity to patient positioning, radiographic magnification, and spinal rotation. Standardized imaging protocols and digital measurement tools help reduce error, and repeated assessments are typically recommended to confirm changes in curvature.