Chapter 11

Incidence refers to the number of new cases of the disease or disorder in the population per year, whereas prevalence is the total number of the cases of the disease or disorder affecting the population at one time. When discussing scoliosis, studies usually give prevalence rates. The results of school screening programs have shown prevalence rates ranging from 0.3 to 15.3%.1–4 This large range is reflective of the different detection methods, population screened, and definition of scoliosis. When only curves of greater than 10 degrees are considered, the prevalence is 1.5 to 3.0%.^1,4 The prevalence rate varies with the curve magnitude: 2 to 3% for curves greater than 10 degrees, 0.3 to 0.5% for curves greater than 20 degrees, and 0.2 to 0.3% for curves greater than 30 degrees.^3,5

♦ Natural History

Once the diagnosis of AIS has been made, options for its treatment include observation, bracing, or surgery. A thorough understanding of the natural history of AIS allows one to make appropriate interventions to alter it in a positive way.

Unfortunately, many of the early long-term natural history studies of idiopathic scoliosis depicted a dismal prognosis. These reports are responsible for the misunderstanding that all types of idiopathic scoliosis will lead to disability from back pain and cardiopulmonary compromise.^6–10 However, these early studies have reported on a mixture of diagnoses including neuromuscular, congenital, infantile, and juvenile scoliosis.

In 1968, Nilsonne and Lundgren¹⁰ reported a 50-year follow-up study of 113 patients with idiopathic scoliosis who were originally seen between 1913 and 1918. The cases were idiopathic, as paralytic and congenital cases were excluded. Ninety percent of the patients were traced, and it was found that 45% had died, with the mortality rate being especially high after the age of 45 years. This mortality rate was twice the rate in the general population, and 60% of the deaths were due to cardiopulmonary disease. Of the surviving patients, 90% had back symptoms and 30% were on disability. Of the females, 76% had never married. The major shortcoming of this study is that no radiographic data was reported, and thus the etiology of these patients’ scoliosis is not clear. Many of the cases were probably infantile in onset.

In 1968, in the same journal as the above article,¹⁰ Nachemson⁹ presented the results of a 38-year follow-up of 130 patients with untreated scoliosis. There was a 100% increase (or twice the rate) in mortality compared with the general population. If only thoracic curves were considered, the mortality rate was 4 times that of the general population. In addition, 37% had constant back pain, 14% complained of cardiopulmonary symptoms, and 37% claimed disability because of their deformity. No one was employed in an occupation requiring heavy labor. The patients, however, had a mixture of different diagnoses. Only 59 patients (45%) had idiopathic scoliosis, and the remainder included patients with congenital scoliosis, paralytic scoliosis, neurofibromatosis, and scoliosis due to tuberculosis. In 1992, Pehrsson et al.11 revisited this patient population and divided the patients into different diagnosis. They found a significantly higher mortality in infantile and juvenile scoliosis but not in AIS.

Although these early studies depicted a dismal natural history for patients with AIS, they are of historical interest because little is known about the study population, most importantly the underlying diagnosis. Today, we have a better understanding of the natural history of AIS. For simplicity, the authors like to divide the natural history of AIS into preskeletal maturity and postskeletal maturity. For preskeletal maturity patients, studies have concentrated on the risk factors for progression of the curve, whereas for the postskeletal maturity, studies present both the radiographic and clinical outcomes of the patients.

Natural History Preskeletal Maturity

In the natural history of idiopathic scoliosis, there are three important questions: What percentage of cases progress? Is it possible to predict which curves will progress? What are the effects of untreated scoliosis? The effects of untreated scoliosis are discussed in the postskeletal maturity sections below.

The progression rates defined as 5 degrees or 10 degrees of increase from the time of presentation are fairly well documented. These progression rates vary from 5.2 to 40% (Table 11–1).^2,12–15 The factors related to curve progression can be divided into those related to the child’s growth potential and factors related to the curve.

It is well-known that scoliosis can progress in the adolescent, especially during the adolescent growth spurt. This relationship between scoliosis and growth was first shown by Duval-Beaupere who studied 560 female scoliosis patients (500 post-polio and 60 idiopathic) with respect to curve progression and growth and compared the findings with the growth of 53 girls without scoliosis.¹⁶ The curves increase at a steady rate during growth until a point called P, when an acceleration of the increase occurred, until a point called R, after which the curve increase plateaued.

Point P coincided with the onset of puberty on the growth velocity graph for girls and boys. In girls, this is marked by the start of breast and pubic hair development, at a Tanner stage 2 or chronological age 10 to 12 years. The growth spurt lasts ~2.5 to 3 years with the point of maximum growth velocity occurring 1 year after the onset of the growth spurt. Menarche, and the appearance of axillary hair, occurs 1.5 to 2 years after the onset of the growth spurt at a mean age of 13 years.¹⁷ In boys, the onset of pubic hair occurs before the onset of the growth spurt. The onset of growth spurt coincides with a Tanner stage 2 or 3 and chronological age 11 to 16 years. The growth spurt is longer in boys, lasting 3.5 to 4 years with peak height velocity occurring at a mean chronological age of 14 years. The appearance of axillary hair and facial hair occur after peak height velocity. All the ages stated are according to a uniform Anglo-Saxon Caucasian population only and cannot be extrapolated for other races. Although the ages do not hold true for other races, the relationship between the maturity landmarks (Tanner stages, peak height velocity, menarche, etc.) and the growth spurt are still accurate.

Point R coincided with a Risser apophyis ossification sign of 4. Risser 4 corresponds with a cessation of spinal growth, and Risser 5 indicates the cessation of height increase.¹⁸

Lonstein and Carlson¹⁴ studied the magnitude of the curve and the maturity of the child (using Risser sign) to determine the rates of curve progression. For curves of 20 to 29 degrees in an immature child with a Risser sign of 0 or 1, the risk of progression was 68%. On the other hand, for curves of less than 19 degrees in a mature adolescent with a Risser sign of 2 or more, the risk of progression was 1.6%. For smaller curves less than 19 degrees in immature children with Risser sign of 0 or 1, the risk of progression was 22%. In similar fashion, for larger curves 20 to 29 degrees but in mature children with Risser more than 2, the risk of progression was also 22% (Table 11–2).

Another clinical factor that has been suggested to be a risk factor for progression is the sex of the child. It is well-known that the prevalence of scoliosis detected on school screening has an approximately equal sex ratio, but those requiring treatment are predominantly female. Although one may expect that studies would show different incidences of progression in girls and boys, this has not been the case as all large series have too few boys to make any statistically significant statement, but some trends can be ascertained.

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Anterior/Posterior (AP) Surgery for Spinal Deformity Anterior Surgery for Thoracic Scoliosis Principles of Sagittal Plane Deformity Technological Advances in Spinal Deformity Surgery Congenital Scoliosis Posterior Surgery for Thoracic Scoliosis

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