How the Cobb Angle Is Used to Measure Scoliosis

Table of ContentsView AllTable of ContentsCobb Angle X-Ray and InterpretationIs It an Exact Science?

Table of ContentsView All

View All

Table of Contents

Cobb Angle X-Ray and Interpretation

Is It an Exact Science?

Cobb angle is a measurement of the degree of side-to-sidespinal curvature, which is a deformity calledscoliosis.

The Cobb angle, named for orthopedic surgery pioneer John Robert Cobb, describes the distance a scoliotic curve may deviate from being straight.Generally, it takes at least 10 degrees of deviation from straight before scoliosis is confirmed.

This article explains the role of the Cobb angle in diagnosing scoliosis.

Oyemi Sillo / Creative Commons 3.0

To get your Cobb angle measured, you’ll need to have an X-ray taken. These generally require you or your child to be in a standing position; side and back views are taken. After that’s done, the healthcare provider or examiner views the films and locates the most affected vertebra in the curve.

This is called theapical vertebra. The apical vertebra in a scoliotic curve is the spinal bone with the greatest degree of rotation; it takes the biggest curve away from the center of a normal spine column.

Visualizing the Cobb Angle

The apical vertebra is where two lines drawn from your X-rays will meet. First, two lines are drawn along the edge of the top and bottom bones of the curve. These lines are extended out as follows:

Then, to come up with a number for the Cobb angle, the top and bottom vertebrae of theside to side curveare identified. Unlike the apical vertebra, these bones have the most tilt, but the least amount of rotation and displacement. They are located above and below the apical vertebra.

Computer-assisted methods are commonly used to calculate the Cobb angle.Treatment decisions are based on the size of the angle, the gender of the individual (scoliosis is more common and likely to progress in females), and the probability of progression.

Treatment for Mild to Severe Dextroscoliosis

A Cobb Angle of 10 Degrees

Scoliosis is diagnosed when the Cobb angle reaches 10 degrees or more. However, this is not generally considered to be a significant curvature.In about 80% of cases, the scoliosis is consideredidiopathic(without a congenital or other underlying cause).

A Cobb Angle of Less Than 25 Degrees

If a scoliotic curve is less than 25 degrees, you may only need to visit your healthcare provider periodically. Watchful waiting may be enough so long as the scoliosis is monitored. This typically means reassessing the Cobb angle every four to six months in a growing child or adolescent.

These are mild cases, often without symptoms, but there is a chance that the curvature can progress. A 5-degree change in Cobb angle (or more) can change the diagnosis and treatment.

A Cobb Angle Between 25 and 40 Degrees

A Cobb angle of 25 to 40 degrees usually requires that a back brace is worn and that you or your child undergo intensive physical therapy. The goal of thesetreatmentsis to help halt the progression of the curve.

Braces are generally worn 16 to 23 hours every day.As for physical therapy, your healthcare provider will likely give you a referral.

Many people report excellent results with the Schroth or otherscoliosis-specific exercise methods. A 2017 study published in theJournal of Exercise Rehabilitation found that Cobb angles can be decreased in adolescents who have idiopathic scoliosis with the use of core stabilization exercise programs.

Scoliosis in AdultsScoliosis is diagnosed in adults, usually in people who have had the condition (treated earlier or not) since it was identified in their youth. A study that followed these cases for 20 years found disease progression occurred in 40% of adults but it was usually less than one degree per year. However, degenerative scoliosis also can occur in people age 65 and older.

Scoliosis in Adults

Scoliosis is diagnosed in adults, usually in people who have had the condition (treated earlier or not) since it was identified in their youth. A study that followed these cases for 20 years found disease progression occurred in 40% of adults but it was usually less than one degree per year. However, degenerative scoliosis also can occur in people age 65 and older.

Physical Therapy for Scoliosis

A Cobb Angle of 40 Degrees or More

Once the Cobb angle reaches 40 to 50 degrees, surgery is considered. Often a spinal fusion is done to force the curve to stop developing. Some 38,000 people complete spinal fusion surgery each year.

In adults, surgery may be needed if the Cobb angle reaches 50 degrees and they experience complications, such as nerve damage or bowel/bladder dysfunction. Risk factors in adults include an older age, a history of smoking, and a diagnosis of other conditions including overweight.

Variations occur in measuring scoliosis, and understanding the difference between a change in the scoliosis and a change in the tools or measurement is important. Equipment errors, imaging errors, and the subjective reading of the healthcare provider can change the values.

Scoliosis measurement software and intelligent medical devices continue to improve the way that scoliosis is evaluated and treated. But keep in mind that physical exams, symptoms, and careful monitoring of changes in posture or function are still critical to an accurate diagnosis.

Summary

The Cobb angle is a mathematical tool for assessing the curvature of the spine. Along with physical exams and other tests, it is used to assess scoliosis andkyphosisof the spine.

The size of the Cobb angle helps to determine what kind of treatment is needed. With a mild curvature, monitoring may be all that’s necessary. With severe scoliosis, treatment may mean spinal fusion surgery.

Bracing and physical therapy are some of the options in between. Your healthcare provider will explain the Cobb angle and other tests results, and discuss any diagnosis with you.

5 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Botterbush KS, Zhang JK, Chimakurty PS, Mercier P, Mattei TA.The life and legacy of John Robert Cobb: the man behind the angle.J Neurosurg Spine. 2023 Sep 8;39(6):839-846. doi: 10.3171/2023.7.SPINE23146.Jin C, Wang S, Yang G, Li E, Liang Z.A Review of the Methods on Cobb Angle Measurements for Spinal Curvature.Sensors (Basel). 2022 Apr 24;22(9):3258. doi: 10.3390/s22093258.National Scoliosis Foundation.Scoliosis Media & Community Guide.American Association of Neurological Surgeons.Scoliosis.Ko KJ, Kang SJ.Effects of 12-week core stabilization exercise on the Cobb angle and lumbar muscle strength of adolescents with idiopathic scoliosis.J Exerc Rehabil.2017;13(2):244-249. doi:10.12965/jer.1734952.476

5 Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Botterbush KS, Zhang JK, Chimakurty PS, Mercier P, Mattei TA.The life and legacy of John Robert Cobb: the man behind the angle.J Neurosurg Spine. 2023 Sep 8;39(6):839-846. doi: 10.3171/2023.7.SPINE23146.Jin C, Wang S, Yang G, Li E, Liang Z.A Review of the Methods on Cobb Angle Measurements for Spinal Curvature.Sensors (Basel). 2022 Apr 24;22(9):3258. doi: 10.3390/s22093258.National Scoliosis Foundation.Scoliosis Media & Community Guide.American Association of Neurological Surgeons.Scoliosis.Ko KJ, Kang SJ.Effects of 12-week core stabilization exercise on the Cobb angle and lumbar muscle strength of adolescents with idiopathic scoliosis.J Exerc Rehabil.2017;13(2):244-249. doi:10.12965/jer.1734952.476

Botterbush KS, Zhang JK, Chimakurty PS, Mercier P, Mattei TA.The life and legacy of John Robert Cobb: the man behind the angle.J Neurosurg Spine. 2023 Sep 8;39(6):839-846. doi: 10.3171/2023.7.SPINE23146.Jin C, Wang S, Yang G, Li E, Liang Z.A Review of the Methods on Cobb Angle Measurements for Spinal Curvature.Sensors (Basel). 2022 Apr 24;22(9):3258. doi: 10.3390/s22093258.National Scoliosis Foundation.Scoliosis Media & Community Guide.American Association of Neurological Surgeons.Scoliosis.Ko KJ, Kang SJ.Effects of 12-week core stabilization exercise on the Cobb angle and lumbar muscle strength of adolescents with idiopathic scoliosis.J Exerc Rehabil.2017;13(2):244-249. doi:10.12965/jer.1734952.476

Jin C, Wang S, Yang G, Li E, Liang Z.A Review of the Methods on Cobb Angle Measurements for Spinal Curvature.Sensors (Basel). 2022 Apr 24;22(9):3258. doi: 10.3390/s22093258.

National Scoliosis Foundation.Scoliosis Media & Community Guide.

American Association of Neurological Surgeons.Scoliosis.

Ko KJ, Kang SJ.Effects of 12-week core stabilization exercise on the Cobb angle and lumbar muscle strength of adolescents with idiopathic scoliosis.J Exerc Rehabil.2017;13(2):244-249. doi:10.12965/jer.1734952.476

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Visualizing the Cobb Angle#

A Cobb Angle of 10 Degrees#

A Cobb Angle of Less Than 25 Degrees#

A Cobb Angle Between 25 and 40 Degrees#

Scoliosis in Adults#

A Cobb Angle of 40 Degrees or More#

Summary#