Etiologies, Pathophysiology, and Clinical Presentation: The reported prevalence of idiopathic scoliosis in children and adolescents ranges from 0.5 to 3 per 100.1,18,19 In the mild curves (<20 degrees), the female-to-male ratio is 1 : 1, but, when greater and progressive curves are evaluated (>30 degrees), females predominate with a 5 : 1 to 7 : 1 ratio. Only 0.2% of children have severe curves (>30 degrees).^1,19,20

Idiopathic scoliosis is further divided into the following types based on age at diagnosis: infantile (0-3 years); juvenile (4-10 years); adolescent (11-17 years); and adult (≥18 years). Age at onset has prognostic significance both in terms of underlying neuraxis abnormality as a cause of scoliosis and the natural history of the curve. Whether juvenile scoliosis is truly a separate entity, is debatable because of the high prevalence of associated abnormalities in preadolescent scoliosis by magnetic resonance imaging (MRI).² Moreover, the demarcation is further obscured by the possibility of early existence of the established adolescent curve. Hence the terms early onset and late onset are increasingly being used to classify scoliosis after the age of 5 years.^2,21 The rationale behind this distinction is the increased risk of cardiopulmonary compromise in children before age 5 years with larger curves.^2,22

Imaging: The role of imaging in scoliosis is early detection and characterization of the type of curve and its severity, assessment of disease progression, definition of the need and timing of the surgery, monitoring of changes related to treatment, and identification of those cases in which an underlying structural anomaly is present.²³ The extent and type of imaging is also governed by the category of scoliosis. Cross-sectional imaging is extensively used in congenital scoliosis to identify and characterize structural anomalies, whereas radiography is principally utilized in idiopathic scoliosis to monitor curve progression.²

Screening: Upright, standing, posteroanterior radiograph of the entire spine is the standard initial screening examination, once the deformity is suspected clinically. The radiograph should include the cervicothoracic junction, enough of the pelvis to show the iliac crest in full extent, and the triradiate cartilage to enable assessment of skeletal maturity. Although standing radiography is preferred, sitting or supine radiography may be the only alternative in young patients, patients with congenital scoliosis, or patients with severe neuromuscular disorders. The rationale behind standing radiography is that treatment methods are based on standing views and the magnitude of the curve is greatest in the standing position. This is an important consideration in congenital and infantile scoliosis when young patients with scoliosis start to ambulate. It is easy to mistake change in curvature as curve progression if the upright radiograph is compared with a prior supine radiograph.¹ The patient should stand with the feet placed shoulder width apart, looking straight ahead with the elbows bent and knuckles in the supraclavicular fossa bilaterally, allowing visualization of the upper thoracic region on the lateral radiographs.²⁴ A lateral radiograph is not required at the time of screening but should be obtained in patients with documented scoliosis to assess sagittal balance. Radiographic techniques should minimize radiation exposure, especially to sensitive organs (e.g., breast, thyroid, and lens of eyes). A posteroanterior technique involves less radiation to the breast compared with an anteroposterior technique. The image may have a grid that helps identify deviations of the spine from the plumb line. When surgical treatment is considered, side-bending radiographs are acquired to differentiate between structural and nonstructural minor curves to help guide the optimal level of fusion. Various techniques used to obtain side-bending radiographs include supine bending, standing bending, and bending over a bolster.

Curve Magnitude: The Cobb angle is the accepted standard for assessing the magnitude of the scoliotic curve. It is defined as the angle formed by the intersection of two lines, one parallel to the end plate of the superior end vertebra and the other parallel to the end plate of the inferior end vertebra. Alternatively, pedicles may be used to calculate the Cobb angle when the end plates are poorly defined because of radiographic technique or obscured because of the severity of the curve. Although the Cobb angle provides limited assessment of the deformity and does not take rotation into account, it is still the foundation for diagnosis, follow-up, and treatment.¹ The angle may be plotted manually or digitally with equal reliability.²⁵ It is important to note that multiple factors, including patient positioning, radiographic techniques, known diurnal variation of 5 degrees, and interobserver and intraobserver variability, may affect the reproducibility of the angle.^26–30 A progressive curve is usually defined by a Cobb angle increase of 5 degrees or more between consecutive radiographic examinations.^1,2,6 The Cobb angle may decrease because of prone positioning and anesthesia during surgery, which sometimes leads to a postoperative rebound effect, with loss of correction when the patient returns to the standing position.^6,13 Despite multiple caveats, measurements of the Cobb angle are usually considered reproducible, particularly when measuring end plates, patient positioning and techniques are kept constant.

Assessing Curve Progression: Prognosis and management in scoliosis is highly specific to the case and the surgeon but is usually governed by three important factors: (1) etiology, (2) magnitude and the type of the curve at presentation, and (3) speed of curve progression. The risk of progression is directly related to the spinal growth remaining, the severity of the curve at presentation, and the gender of the patient.1,10,19,31,32 Various clinical tools to assess residual growth potential include chronologic age, menarche in girls, serial height measurements, and Tanner staging.^{10,19,33–37} In general, the onset of the adolescent growth spurt occurs at 13 years in boys and 11 years in girls, with menarche indicating the declining phase of the growing peak and a low risk of progression for idiopathic curves under 30 degrees.^1,10,33,35 Various radiographic parameters may indicate remaining potential growth. Development of the iliac bone apophysis, quantified by Risser, has become a universally accepted sign (Fig. 135-2). Despite the wide use of the Risser grade as a measure of maturity, the appearance of the iliac apophysis generally occurs after the most important period of rapid growth.^1,33,34 Given the inaccuracies related to the Risser grade, other radiographic parameters are used to assess bone maturation. Bone age may be assessed from a hand and wrist radiograph; however, use of bone age becomes less accurate in the juvenile age group secondary to the larger standard deviation and suffers from interobserver variability.^1,38 Assessment of pelvic triradiate cartilage is considered more accurate than the Risser grade. The triradiate cartilage closes around age 11 years in girls at the time of peak growth velocity.^1,23 The physis of the olecranon of the elbow closes at age 13 years, shortly before menarche and may also be used to assess remaining skeletal growth.²³ Unfortunately, many of the above-mentioned markers of maturity are quite variable and may be difficult to put in proper context without an accurate record of prior growth performance. Sometime, more than one imaging parameter is taken into consideration for accurately assessing skeletal maturation.

With regard to curve patterns, curves with an apex above T-12 are more likely to progress compared with isolated lumbar curves.¹ With regard to curve magnitude