Cobb Angle or Balance? Trends, Debates in Scoliosis Orthotic Management

Home > Articles > Cobb Angle or Balance? Trends, Debates in Scoliosis Orthotic Management
By Miki Fairley

My dad was the first to notice that something was wrong. One day when he was walking behind me, he could see that one shoulder blade was more prominent than the other. When we got home, he looked at my back, and it was obvious something wasn't right. They immediately took me to a doctor, who took an X-ray of my spine. I remember thinking that my spine looked really weird in the X-ray, and that scared me. It turns out I had a fairly severe 68-degree curve in my spine, and the doctor recommended surgery as soon as possible.- scoliosis patient

For those youngsters with adolescent idiopathic scoliosis (AIS), catching curves early and beginning bracing can be key to preventing surgery as well as helping to prevent pain and complications later in life. Early bracing can also provide adolescents with a better, more normal appearance, thus helping to improve self-esteem during this vulnerable stage of life.

Even if surgery should become necessary, it often is not a permanent solution, since back pain and other complications can present later in life, perhaps requiring additional surgery.


Orthotic designs are improving relative to comfort and cosmesis, thus aiding patient compliance. However, as in many areas of medicine and allied health, there are still many unknowns about the orthotic management of AIS. This article explores some of these issues, noting that there is disagreement among experts on some controversial aspects of orthotic management of AIS.

When it comes to scoliosis requiring treatment, girls outnumber boys about seven to one, notes Don Katz, CO, FAAOP, assistant administrator and director of Orthotics at Texas Scottish Rite Hospital for Children, Dallas.

"We need to catch curves when they are smaller, before kids enter their primary adolescent growth spurt, because that's when primary curves are most likely to get worse," Katz adds. Girls typically begin their adolescent growth spurt before menarche-most commonly between ages 11-13.

"We want to halt curve progression and avoid surgery, so we want to brace kids before they get to that point. We want to catch scoliosis patients when the curve is large enough that there is a reasonable assumption that it is going to progress, but ideally when it's less than 30 degrees," Katz says. Most patients with measurable curves greater than ten degrees don't end up requiring treatment, he explains. "But there is that small subset of patients that go to 20 degrees. Then we ask ourselves, should we start bracing, or should we wait a bit longer for documented progression to 30 degrees? For a skeletally immature child with a curve greater than 30 degrees, orthopedists generally will begin bracing. However, the question arises for those between 20 and 30 degrees. Is this not going to get worse, or is it going to progress quickly into the 30s and 40s?

"The thinking has been to continue to brace until maturity is achieved, but it's difficult to define just when that occurs. Conventional wisdom suggests maturity is assured when a Risser sign of 5 is achieved, but considering the entire spectrum of patients being treated with an orthosis for AIS, that can be overkill for a lot of patients," Katz continues. For instance, there might be girls who are four years post-menarche before they reach Risser 5, Katz says, but spinal growth is minimal after about two years post-menarche, which would be Risser 4."In the context of maturity, we need research to tell us truly how long a child should be braced. For instance, I'd be more inclined to brace a child with a larger curve that is less balanced longer than another girl with a mild curve that has shown no propensity to progress. In the latter case, we might take her out of the brace a little earlier. Every child has to be dealt with separately. The safe time to take off a brace is when there is no significant growth remaining."

Thus, the Risser sign, which, in the frontal plane X-ray of the pelvis, shows the state of ossification of the iliac apophysis to denote the degree of skeletal maturity, may not be the absolute indication of maturity relative to bracing. What other factors could help focus the time of maturity?

James Sanders, MD, of the Philadelphia, Pennsylvania, Shriners Hospital for Children, and others "have done recent exciting work on maturity markers," Katz notes.

[Editor's note: For more information, visit ]


What's wrong with the Cobb angle?

Not fully descriptive of the relationship of the vertebral tilts that combine to form the angle itself.

This illustrates that the Cobb angle is a summation of the angles measured of the two most tilted vertebrae in the curve.

The role of the "transitional vertebra."

This illustrates that when a Cobb angle is successfully reduced with an orthosis, the amount of vertebral tilt correction is often not symmetric; i.e., the tilt of the one vertebra making the Cobb angle is often corrected more than the other.

The balancing of forces?

An example of a relatively balanced scoliotic spine becoming less balanced, despite a reasonable reduction in the measured Cobb angles. The Cobb angle of the lumbar curve is reduced at the expense of significantly increasing spinal decompensation to the left. This warrants immediate changes to the corrective forces being applied by the orthosis.

Photos and illustrations courtesy of Texas Scottish Rite Hospital for Children.

Spinal Balance vs. Cobb Angle

Katz participated in a panel discussion titled "Trends in Adolescent Idiopathic Scoliosis Concerning Cobb Angle vs. Overall Balance and the Application of Forces" during the 2006 Annual Meeting of the American Academy of Orthotists and Prosthetists (the Academy). Other panelists were Andrew Mills, CO (UK); Keith Smith, CO, LO; Thomas H. Colburn, CO, FAAOP; and J. Martin Carlson, CPO, FAAOP.

The panelists discussed the question of how important overall spinal balance is relative to trying to obtain a maximum reduction of the Cobb angle. All panelists were asked to address the primary question: "Does the Cobb angle possess the key attributes of validity, reliability, and sensitivity, and if so, does it adequately serve the patient as a measure of idiopathic scoliosis treatment and outcome?"

As to validity, Katz notes that the Cobb angle has been the standard since 1948 as the primary method of quantifying the degree of deformity, both in vertebral limits and size. The Cobb angle drives clinical decision making and is the primary measurement by which all natural history studies have been conducted as well as subsequent studies on orthotic treatment and indications for surgery.

Regarding reliability, Katz quotes from a study by Carman, et al., published in the Journal of Bone and Joint Surgery (JBJS) in 1990 that says, "If one were to be 95 percent confident that a measured difference represented a true change, the difference would have to be ten degrees for scoliosis radiographs." He notes that there is measurement error of plus or minus five degrees for a single radiograph.

Katz points out that, as noted by Appelgren and Willner in Spine, 1990, that there can be varying patterns with the same thoracic Cobb angle and the same vertebral endpoints.

The abstract for the Academy presentation notes, "Scoliosis orthoses are designed for children with adolescent idiopathic scoliosis through a combination of clinical and radiographic evaluation. The standing PA X-ray is an essential tool for designing or blueprinting the scoliosis orthosis. The most frequently referenced barometer of curve correction is the Cobb angle reduction in an orthosis. The Cobb angle is helpful for quantifying the magnitude of a scoliosis curve but is limited in scope to a two-dimensional angular relationship between two angulated vertebrae and does not relay the complex nature of a three-dimensional individual curve.

"One example of the limitations of the Cobb angle are seen in patients who may have a significantly decompensated curve which measures as a small Cobb angle primarily because the inferior vertebral endpoint is angulated, but the superior vertebral endpoint is more horizontal and does not angulate back toward midline. In the situation of two patients with identical inferior endpoint angulations with one patient decompensated to one side and one patient fully compensated and balanced, the decompensated scoliosis patient would have a smaller Cobb angle than the more balanced, fully compensated scoliosis patient. Cobb angle reference alone would not identify this. The orientation of the scoliosis curve in relation to the central sacral line on radiograph or the overall clinical balance of the trunk is a relationship which should be closely evaluated."

Which leads to the question: "Is it more important to achieve overall balance or maximum reduction of the Cobb angle?"

This is an area of debate, with pros, cons, and a need for more research.

Examining Both Sides of the Coin

A scatter plot illustrating the change in curve size from the start of treatment to the time of brace discontinuation, plotted against the actual average hours of wear throughout treatment, as monitored through the use of a temperature data logger. In this population of Risser 0 or 1 patients treated with a Boston Brace for AIS, the amount of time in which the brace was worn was shown to have a highly significant influence on preventing curve progression.
A scatter plot illustrating the change in curve size from the start of treatment to the time of brace discontinuation, plotted against the actual average hours of wear throughout treatment, as monitored through the use of a temperature data logger. In this population of Risser 0 or 1 patients treated with a Boston Brace for AIS, the amount of time in which the brace was worn was shown to have a highly significant influence on preventing curve progression.

Katz notes both the potential benefits and the caveats of both. "A balanced, double curve pattern, each measuring 50 degrees, can be significantly more cosmetic than an unbalanced, single curve at 40 degrees. In general, larger single curves tend to be less cosmetic; the imbalance is more noticeable." However, there is no evidence that suggests an unbalanced spine, or AIS in general, impedes youngsters' function in sports and other activities, Katz says. In extremely severe cases, such as are sometimes seen in developing nations, scoliosis can compromise pulmonary and cardiac functions, but these types of cases are extremely rare in the United States.

Papers on the role of balance in scoliosis management have been out for several years, Katz says. "There has been more interest recently, I think, because we've gone a bit too far in focusing only on the Cobb angle. A brace shouldn't be judged solely on its ability to reduce the Cobb angle. It's entirely possible to reduce the Cobb angle and make the balance worse. From a cosmetic point a patient can look okay because she has balanced curves. If we straighten out the curves, but they become less balanced in the process, we haven't necessarily achieved a good result."

Is it a good idea, then, as has been proposed by some, to induce or allow a secondary curve to achieve a more balanced, more cosmetically appealing spine?

"A common example would be a significantly shifted single thoracolumbar curve-or a lumbar curve," Katz answers. "We could then reason, let's shift this over as much as we can and basically induce a balancing thoracic curve.' That makes sense from a biomechanical standpoint."

Katz continues, "However, the success rates of treating a double curve-a lumbar and thoracic curve combination or any type of double thoracic curve-are lower than treating single lumbar or thoracolumbar curves. So if we induce a curve that can become structural or, even worse, shows signs of progression beyond that which is required to balance the spine, perhaps we might be introducing a problem. That's the debate, and I'd love to see us find some more definitive answers."

Compliance is another issue. To put a child in an almost intolerable brace to squeeze out a few more degrees in reduction of the Cobb angle is not a good idea, Katz says, since patient acceptance and compliance are keys to success. Although a 50-percent in-brace reduction of the Cobb angle has long been the target value, there is no true statistical analysis to support this, he points out. However, none of the more standard "balance" measurements, such as coronal decompensation, apical vertebral translation, relative apical distance, and thoracic trunk shift has been shown in clinical studies to significantly correlate with treatment success of failure.

During the Academy discussion, Katz's conclusion summarized these points:

  • While in-brace correction is important, it shouldn't be at the expense of tolerance.
  • The amount of time an orthosis is worn has a greater influence on treatment success than maximum in-brace correction.
  • We need to define how best to quantify balance, in conjunction with the Cobb angle, and determine its overall influence on outcome.

More Knowledge Needed

Katz identifies several areas for additional research.

Better orthotic design: "We need to learn more about how to be able to provide a scoliosis orthosis that is tolerable but still reduces the Cobb angle to a reasonable degree and that does not flatten the spine in the sagittal plane. Adolescent idiopathic scoliosis typically already flattens somewhat in the sagittal plane. What I think we're doing with a lot of thoracic designs is making a spine that is already somewhat hypokyphotic more hypokyphotic. Based on a number of studies, the tendency is to make a flat spine even flatter. We need to continue to try to develop spinal orthoses that are more accepting, more cosmetic, and more comfortable."

Reliable wear-pattern codifying: Another need is a reliable and simple method to codify actual patient wear patterns for scoliosis orthoses, since the number of hours a day the brace is worn is vital to a successful outcome.

Earlier patient identification: The orthopedic community needs to continue efforts to identify earlier patients who have smaller curves and who are most likely to benefit from bracing.

Finding etiological answers: Another large unknown is why some kids develop curves while most do not, and of those who do develop curves, which ones are likely to progress and need treatment. "There are countless research efforts on factors-blood chemistry, genetics, levels of melatonin, etc."

Although there is still much unknown about adolescent idiopathic scoliosis, more is continually being learned through research and clinical application. Answers are out there-and at least some of them are being found.

Editor's note: To read more about the Cobb angle versus balance debate, see " Adolescent Idiopathic Scoliosis: Cobb Angle Relative to Overall Balance ," by Andrew J. Mills, CO (UK), along with additional articles on AIS bracing, exclusively online.

Miki Fairley is a contributing editor for  The O&P EDGE and a freelance writer based in southwest Colorado. She can be contacted via e-mail at .