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The Natural History of Adolescent Idiopathic Scoliosis

Weinstein, Stuart L. MD

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Journal of Pediatric Orthopaedics: July 2019 - Volume 39 - Issue - p S44-S46
doi: 10.1097/BPO.0000000000001350
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Adolescent idiopathic scoliosis (AIS) is characterized by a lateral curvature of the spine of ≥10 degrees with vertebral rotation. The diagnosis is one of exclusion made only when other causes of scoliosis have been ruled out. About 2% to 3% of children younger than 16 years of age will have a curvature of ≥10 degrees, and 0.3% to 0.5% of these will have a curvature of 20 degrees, the curve magnitude at which treatment is generally recommended.1

Two long-term evaluations of patients with untreated scoliosis were published in 1968.2,3 These studies profoundly influenced physician, patient, and public health policy decisions for decades. The grim prognosis for patients with scoliosis painted in these studies was unfortunate. These studies had the usual shortcomings of a retrospective case collection, but had other considerable limitations, the most important being including scoliosis of mixed etiologies including early-onset idiopathic cases as well as nonidiopathic etiologies such as congenital malformations, polio, and neuromuscular disease. As a consequence of these reviews the misperception that all types of scoliosis inevitably lead to high mortality rates, disability from back pain, and cardiopulmonary compromise was promulgated. And for many years these studies were to form the basis of recommendations for treatment and screening policies.

Most patients present to orthopaedic surgeons not because of symptoms but as a result of screening exam or the findings of truncal asymmetry. Treatments are in general to prevent future consequences. Treatment of any condition is necessary only if the natural history of that condition causes future adverse consequences. For AIS the current natural history data is limited and most of the information comes from a small body of literature from the University of Iowa.4–9 As a result, each patient must be considered individually and the generalities presented in this paper may or may not apply to an individual patient.


The Iowa natural history studies began as retrospective reviews but as will be outlined, beginning in 1976, the cohort was subsequently followed prospectively. In 1950, Ponseti and Friedman4 reported on 394 patients with untreated AIS at the 2-year follow-up. This paper, identified the 4 common curve patterns (Fig. 1) seen in AIS and demonstrated that early prognosis was a function of the curve pattern and age of onset. A second follow-up in 1969 presented evidence to support the relatively long-term natural history of AIS by evaluating not only radiographs, but also pulmonary and back symptoms as well as aspects of patients’ living situations, including occupation, activities, marriage, and children, and comparing the patients’ status to those of a nonscoliotic control group.5

The common curve patterns in adolescent idiopathic scoliosis.4

Beginning in 1976, the author began to follow this cohort prospectively: evaluating radiographic, clinical, and psychosocial outcomes.6 Another report of this cohort focused on factors related to curvature progression.7 A third study, a subset of the patients who had radiographs available from the initial presentation, at skeletal maturity, and at the 30 and 40-year follow-ups was examined demonstrating that the risk factors leading to major curve progression prior to skeletal maturity also predicted continued progression after maturity.8 Finally, this unique cohort of untreated patients was again studied in the 1990s, at an average of 51 years after diagnosis, when the average age of the patients was 66 years.9

Outcomes assessed in this group of patients included: mortality, pulmonary function, pregnancy (effect of pregnancy on scoliosis and the effect of scoliosis on pregnancy), radiographic, major curve progression, and osteoarthritis. In addition, validated questionnaires were used to evaluate back pain, pulmonary symptoms, general function, depression, and body image.

All patients were seen and examined by the author at 40 and 51-year average follow-ups. Physical examinations included: vital signs, height, weight, spinal range of motion, chest expansion, reflexes, motor examination, sensory examination, and nonorganic physical signs. The average major curve magnitude in this cadre was significant (Table 1).

Major Curve Magnitude Average Cobb Angle at Final Follow Up9

At the 40-year and 51-year follow-up the patients were matched to a control group. At their final follow-up the control group came from patients screened at University of Iowa nonorthopaedic clinics, senior citizens centers, and retirement homes. All control patients were screened by the Adams forward bend test, and all had a negative history of spinal curvature. The patients were age and sex matched.


In the clinical situation, most decisions are made based on the major curve magnitude and the risk of curve progression, the assumption being that if the curve progresses the patient may have future problems. These include pain, increased risk of mortality, increasing deformity, and increasing negative psychosocial effects.

Major Curve Progression

Factors in determining major curve progression include curve location and magnitude and skeletal maturity as determined by age, onset of menses, closure of the tri radiate cartilage, Risser sign, and Sanders score. In 1982, Nachemson, Lonstein, and Weinstein (the SRS Natural History Committee) presented a “risk of progression” chart based on data from AIS studies from Sweden, Minnesota, and Iowa (Fig. 2).10

Probabilities of major curve progression: (skeletally immature patients).

In total, 68% of the major curves in our Iowa cohort of untreated patients progressed after skeletal maturity. In general, major curves <30 degrees at skeletal maturity tended not to progress, regardless of the curve pattern. Major curves measuring between 50 degrees and 75 degrees at maturity, particularly thoracic curves, progressed the most. Major curves with both thoracic and lumbar involvement tended to balance with age and maintain coronal compensation.

Pulmonary Function and Symptoms

Pulmonary symptoms are the only symptom in untreated AIS associated with curve size. Other factors affect pulmonary function including thoracic lordosis, vertebral rotation, and respiratory muscle strength. Having a Cobb angle of ≥50 degrees at skeletal maturity is a significant predictor of decreased pulmonary function. Patients with large major curves (>80 degrees) and a thoracic apex had significantly greater odds of shortness of breath than did patients with large major lumbar curves (>50 degrees). Unlike early onset adolescent idiopathic scoliosis (EOS); in AIS, pulmonary hypertension, and right heart failure would be extremely rare. Contrary to the earlier reports from Sweden, we found no evidence to link untreated AIS with increased rates of mortality in general or with cardiac or pulmonary conditions potentially related to the curvature. With that said one must be cognizant of the effect of aging on pulmonary function particularly in patients with severe thoracic curves.11,12

Back Pain

With respect to self-reported history of back pain, 50% of adults without scoliosis have an episode of low back pain in any particular year with 15% reporting frequent back pain or pain that lasts >2 weeks in a given year.13 In AIS, back pain may arise in any patient regardless of curve size or location. Patients with AIS had more chronic back pain and more acute pain of greater intensity and duration than their peers. Most patients developed radiographic osteoarthritic changes over time. A history of back pain in this group is unrelated to the presence or absence of osteoarthritic changes or to the severity of the curve. Back tenderness (with history of pain) was related to the presence of translatory shifts at the lower ends of lumbar and thoracolumbar curves. However, their ability to work and perform activities of daily living was similar to that of controls. Despite back pain, this group of untreated patients continues to function at a high level, indicating that the natural history of AIS does not necessarily include functional disability.

Marriage Rates and Reproductive Experiences

Contrary to the aforementioned 1968 studies, marriage rates in AIS are the same as controls. It has also been well documented in the literature and in this cohort that the reproductive experiences of women with scoliosis do not differ markedly from nonscoliotic women. There is no indication that becoming pregnant in the face of scoliosis will cause curve progression, nor is their evidence of any negative effects on pregnancy in women who have scoliosis (eg, the need for c-section).

Psychosocial Aspects

The psychosocial and depression indices were similar in AIS patients to those of controls. AIS patients were however were generally dissatisfied with their physical appearance. The major curve Cobb angles at the final follow-up ranged from 15 degrees to 156 degrees, with the largest Cobb angle measurements occurring in patients with thoracic or thoracolumbar curves. Many had substantial apical vertebral rotation adding to the deformity in the coronal plane. Therefore, it is not surprising that patients were considerably less satisfied with their appearance than controls. In total, 32 percent felt that their life was limited because of scoliosis, including difficulty purchasing clothes, decreased physical activity, and self-consciousness. Many expressed that while they had had “good lives,” they wished that surgical options had been available to them when they were young so they could have had “a choice.”


The summary findings of this unique lifetime natural history of AIS patients provides patients and parents a solid evidence base upon which to make informed decisions. By closely studying this group of patients for >50 years, we have learned that patients with untreated AIS can function well as adults, become employed, get married, have children, and grow to become active older adults. Unfortunately, untreated scoliosis may lead to increased back pain and pulmonary symptoms for patients with large thoracic curves. Patients with untreated AIS can also develop substantial deformity, and the cosmetic aspect of this condition cannot be disregarded. The physical outcomes demonstrated in this cohort born many decades ago can be used to predict the likely experience of future patients, although we doubt that a contemporary cohort (and their peers) would be as accepting of deformity as these patients have been.14


1. Weinstein SL, Dolan LA, Cheng JC, et al. Adolescent idiopathic scoliosis. Lancet. 2008;371:1527–1537.
2. Nilsonne U, Lundgren KD. Long-term prognosis in idiopathic scoliosis. Acta Orthop Scand. 1968;39:456–465.
3. Nachemson A. A long term follow-up study of non-treated scoliosis. Acta Orthop Scand. 1968;39:466–476.
4. Ponseti IV, Friedman B. Prognosis in idiopathic scoliosis. J Bone Joint Surg Am. 1950;32:381–395.
5. Collis DK, Ponseti IV. Long-term follow-up of patients with idiopathic scoliosis not treated surgically. J Bone Joint Surg Am. 1969;51:425–445.
6. Weinstein SL, Zavala DC, Ponseti IV. Idiopathic scoliosis: long-term follow-up and prognosis in untreated patients. J Bone Joint Surg Am. 1981;63:702–712; 10.
7. Weinstein SL, Ponseti IV. Curve progression in idiopathic scoliosis. J Bone Joint Surg Am. 1983;65:447–455.
8. Weinstein SL. Idiopathic scoliosis. Natural history. Spine (Phila Pa 1976). 1986;11:780–783.
9. Weinstein SL, Dolan LA, Spratt KF, et al. Health and function of patients with untreated idiopathic scoliosis: a 50-year natural history study. JAMA. 2003;289:559–567.
10. Nachemson A, Lonstein J, Weinstein SL. Report of the Prevalence and Natural History Committee, Scoliosis Research Society; 1982.
11. Redding GJ. Early onset scoliosis: a pulmonary perspective. Spine Deformity. 2014;2:425–429.
12. Stanojevic S, Quanjer P, Miller MR, et al. The Global Lung Function Initiative: dispelling some myths of lung function test interpretation. Breathe. 2013;9:463e74.
13. Deyo RA, Mirza SK, Martin BI. Back pain prevalence and visit rates: estimates from U.S. national surveys, 2002. Spine (Phila Pa 1976). 2006;31:2724–2727.
14. Weinstein SL, Dolan LA. The evidence base for the prognosis and treatment of adolescent idiopathic scoliosis: the 2015 orthopaedic research and education foundation clinical research award. J Bone Joint Surg Am. 2015;97:1899–1903.

adolescent idiopathic scoliosis; AIS; natural history; pulmonary function; back pain; general function; outcomes; curve progression; pregnancy

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