Natural History

General Information :: Natural History :: Bracing :: Surgery

Natural History of Adolescent Idiopathic Scoliosis

You can think of the “natural history” of a disease as its course over time if it is not treated. For example, the “natural history” of malignant lung cancer is a very poor prognosis, with death within a couple of years. It is important to understand the natural history of a disease because without this knowledge, one cannot make rational decisions on treatments and timing of treatments. A physician has to have an understanding of what will happen to a patient with a given disease if nothing is done. “What will happen to this patient with scoliosis if no treatment is provided?” The answer to this question is the “natural history” of scoliosis.

The natural history of most patients with adolescent idiopathic scoliosis is fairly benign. Most patients with scoliosis do very well long-term and are fully functional and active adults. This is why most patients are observed and treatment is only recommended for curves that are worsening. A small percentage of patients have curves that are “progressive” and these patients may develop severe scoliosis. Curve progression (i.e. worsening of the curvature) is the single most important parameter that determines treatment and its timing. The problem is that it is often very difficult to predict which curves will progress and which curves will remain the same. A patient’s skeletal maturity is a key factor. So is the size of the curve at time of diagnosis and the location of the curve (thoracic, thoracolumbar, lumbar). There are many factors that must be considered and there are several areas of controversy. However, the following are agreed upon by the vast majority of orthopaedic surgeons who perform scoliosis surgery and can serve as a general guideline:

  • Patients who are skeletally immature (e.g. premenarchal girls) with curves greater than 25 degrees are at high risk of progression. It is not known precisely what percentage of these patients progress to the point of needing surgery, but it is generally believed that this is a “high risk” group that requires very close observation. Treatment with bracing is generally recommended in these patients if the curve is between 25 and 40 degrees. For more on bracing for scoliosis, click here.
  • Patients who are skeletally immature (e.g. premenarchal girls) with curves greater than 50 degrees require surgery. These patients are likely to develop very severe curves (over 70-80 degrees) and it is better to treat these curves with surgery before the curve becomes that severe.
  • Patients who are skeletally mature (growth plates closed, at least 2 years postmenarchal) with curves less than 30 degrees do very well long term and risk of significant progression into adulthood is very low.
  • Patients with curves over 60 degrees (regardless of skeletal maturity) are treated surgically because of the high risk of developing severe deformity in adulthood.

Beyond the above, there is debate among orthopaedic surgeons with regard to the long-term natural history of scoliosis. While it may be easier to predict how a curve will behave in the short-term (say over 5-7 years), it is far more difficult to look 30-40 years into the future and try to predict what will happen. And herein lies the challenge of treating scoliosis: The task of the orthopaedic surgeon is to predict the effects of the scoliosis far into the future, and thus determine whether surgical treatment should be recommended now or sometime in the future if the curve does become symptomatic or continues to progress. One would need a “crystal ball” to predict what will happen to a 40 degree curve in 50 years. The truth is that no one knows for certain, and each patient is going to determine his or her own unique natural history.

This is why you may get different opinions on treatment if you get 2nd or 3rd opinions from surgeons. The reason surgeons may disagree on treatment recommendations is because no one really knows for certain what will happen to your child’s curve in 40 years. The average orthopaedic surgeon practices for approximately 30-35 years, and some practice for 40 or more years. To be able to follow a teenage patient for that long a time to see what happens to their scoliosis is not practical and rarely happens. So surgeons rely on published studies on natural history, and even the best studies have a limited number of patients (because it is hard to follow patients over 40-50 years time), which makes it difficult to make any definitive recommendations.

Most authors would recommend surgery for the skeletally mature adolescent or young adult with a curve larger than 55 to 60 degrees due to the high risk of significant progression into adulthood. Furthermore, most would agree that curves less than 40-45 degrees in skeletally mature patients can be observed. Decision making is not as well-defined in skeletally mature patients with curves between 45-55 degrees and there is great variability in how these patients are treated. The best studies, with the longest follow-up have a small number of patients with curves in this range. While it has become common for orthopaedic surgeons to recommend surgery when a curve reaches 50 degrees, not all of these curves progress to a degree that leads to problems in adult life. However, as patients age and other medical comorbidities develop, surgical risks increase, and therefore surgery at a younger age may be a good idea in certain cases even in the absence of documented progression.

So far, the discussion has focused on curve size and curve progression. Other factors also need to be considered, as follows:

Internal Organs and Scoliosis

Does scoliosis affect the function of internal organs (i.e. heart and lungs)? The answer to this question is not a straightforward “yes” or “no”. As mentioned earlier, there are different types of scoliosis, with adolescent idiopathic scoliosis being just one of them. Scoliosis that develops in infants and very young children (called early onset scoliosis) has a much worse prognosis long-term in terms of heart and lung function. In most cases of adolescent idiopathic scoliosis, the heart and lungs are not significantly affected unless the curve becomes very severe (i.e. over 90 degrees). Most curves do not reach this stage, partly because surgery is recommended when the curve reaches 50-60 degrees. However, it depends on how one defines heart and lung compromise. It is rare for the heart or lungs to “fail” as a result of scoliosis, but it is certainly more likely that the diminished function of the lungs may cause some problems for an elderly patient As an example, consider a 75 year old patient who has a 65 degree scoliosis. This patient may not have heart or lung failure, but her lungs do not have as much room or “capacity” as a patient her age without scoliosis. So if this patient develops a pneumonia, for instance, she may have more difficulty recovering from this illness and so the scoliosis may affect her in this regard.

Back pain and Scoliosis

Does scoliosis lead to back pain in later life? Again, this is a difficult question to answer. The available long-term studies on adolescent idiopathic scoliosis suggest that chronic back pain is more common in patients with scoliosis but that the duration and intensity of the pain, and ability to work and perform daily activities is similar to peers without scoliosis. As arthritis develops in older age, the scoliosis that was previously painless in the teenager may cause pain in older age, but this is not the case in all patients. Generally, in a teenager who has no or minimal back pain, one should not consider surgery because of the potential for back pain developing in older age as a result of the scoliosis.

Cosmestic Concerns and Scoliosis

Is the deformity that is caused by scoliosis a problem? And should surgery be done for cosmetic reasons in the absence of other problems? The deformity caused by scoliosis is quite variable. Some patients with severe curves have little apparent deformity while others with milder curves have more clinically apparent deformities. There are several reasons for this, the main one being the degree of rotation of the vertebrae. The more rotated the vertebrae are, the more prominent the ribs will appear in the back. Thinner patients tend to have more apparent deformities, while more muscular and heavy-set patients tend to hide their deformity fairly well.

A patient’s psychological makeup greatly influences the degree of dissatisfaction with appearance. Some patients with severe curves accept their deformity while others with mild curves have significant cosmetic concerns.

In contrast to adolescents, cosmetic concerns are rarely an issue in adults with scoliosis, particularly in patients over the age of 40. Not surprisingly, most patients are more self-conscious about their deformity in the adolescent and young adult years than in older age. This point should be discussed with the young patient with scoliosis, that cosmetic concerns tend to fade and become less prominent as she gets older.


Natural history studies reveal a favorable natural history for adolescent idiopathic scoliosis. Except for some increase in back pain and cosmetic concerns, patients tend to function fairly well into adulthood despite severe deformities. Mortality rate is not increased compared with normal controls. Although thoracic curves greater than 100 degrees may predispose to heart and lung complications, progression to this degree is unusual. Curves greater than 50 degrees at skeletal maturity may be treated surgically to prevent severe deformity in adulthood, but this recommendation is based on a small number of patients in long-term follow-up studies. Each patient ultimately determines his own natural history and long-term x-ray follow-up is important if nonsurgical treatment is chosen.