Cobb angle

Measurement of spinal curvature in scoliosis

Cobb Angle

The Cobb angle is a measurement used to quantify the degree of spinal deformities, particularly in cases of scoliosis. It is named after the American orthopedic surgeon John Robert Cobb, who developed the method in 1948. The Cobb angle is the most widely used method for assessing the severity of scoliosis and is crucial in determining the appropriate treatment plan for patients.

Diagram illustrating the measurement of the Cobb angle in scoliosis.

Measurement Technique

To measure the Cobb angle, a healthcare professional will typically use an X-ray of the spine. The process involves the following steps:

1. Identify the most tilted vertebrae at the top and bottom of the spinal curve.
2. Draw a line parallel to the superior endplate of the top vertebra and another line parallel to the inferior endplate of the bottom vertebra.
3. Erect perpendicular lines from these two lines.
4. The angle formed at the intersection of these perpendicular lines is the Cobb angle.

The Cobb angle is expressed in degrees and provides a quantitative measure of the curvature of the spine.

Clinical Significance

The Cobb angle is essential in the diagnosis and management of scoliosis. The severity of scoliosis is often categorized based on the Cobb angle:

• Mild scoliosis: Cobb angle less than 20 degrees.
• Moderate scoliosis: Cobb angle between 20 and 40 degrees.
• Severe scoliosis: Cobb angle greater than 40 degrees.

Treatment decisions, such as observation, bracing, or surgical intervention, are often based on the magnitude of the Cobb angle and the progression of the curve.

Limitations

While the Cobb angle is a valuable tool, it has some limitations. The measurement can be affected by the quality of the X-ray image and the skill of the person measuring the angle. Additionally, the Cobb angle does not account for the three-dimensional nature of spinal deformities, as it only measures the curvature in the coronal plane.

Related Pages

• Scoliosis
• Spinal deformity
• Orthopedic surgery