Chapter 100 Pediatric Spinal Deformities and Deformity Correction

Brian J. Williams, Justin S. Smith, Christopher I. Shaffrey

Pediatric spinal deformity can result from congenital anomalies, neuromuscular disorders, genetic conditions, connective tissue disorders, skeletal dysplasia, and developmental (idiopathic) causes.^1,² Each category of spinal deformity has a typical behavior dictated by the pathophysiology of the underlying condition.

Scoliosis, kyphosis, and lordosis refer to deviations from normal spinal alignment. In the coronal plane, the spine is normally straight. In the sagittal plane, the thoracic region is kyphotic (range, 20–40 degrees), the lumbar region is lordotic, and the transition over the thoracolumbar region is relatively straight (Fig. 100-1).³ Scoliosis, curvature in the coronal plane, is also associated with transverse rotation, as well as with pathologic lordosis or kyphosis (Figs. 100-2 and 100-3).³^–⁵ Therefore, the terms lordoscoliosis and kyphoscoliosis are frequently used to characterize the three-dimensional nature of a deformity. When more than one pathologic curvature exists along the length of the spine, the primary (or major) curve is designated on the basis of its size and rigidity. The secondary (or minor) curve(s), even if compensatory, may be rigid or have a “structural” component. Surgical planning should address the magnitude and flexibility of all the curves in all three planes.

FIGURE 100-1 Spinal sagittal alignment is shown with the segmental angulation between vertebrae.

(From Bernhardt M, Bridwell KH: Segmental analysis of the sagittal plane alignment of the normal thoracic and lumbar spines and thoracolumbar junction. Spine [Phila Pa 1976] 14:717–721, 1989, with permission.)

FIGURE 100-2 A, Idiopathic scoliosis is a three-dimensional deformity, typically associated with thoracic hypokyphosis or lordosis. B, The rib cage deforms so that the right dorsal rib angle becomes more prominent, and the left breast projects forward. The star-shaped body is the inferior vena, which is positioned next to the aorta in the posterior mediastinum. C, The end vertebrae of the scoliosis are most tilted, whereas the apical vertebrae are most rotated and laterally translated.

FIGURE 100-3 A, The Cobb angle for scoliosis measurement is formed by the intersection of perpendicular lines drawn to the end plates of the most tilted vertebrae. B, In this case, the Cobb angle measures 52 degrees.

Growth of the Spine

Pediatric spinal deformities are usually not clinically evident at birth. However, they progress in proportion to spinal growth. Therefore, anticipating and modifying the growth potential of the vertebral elements composing the deformity is essential. Two periods of rapid growth occur in children: the first between birth and 3 years and the second during the adolescent years. The timing and duration of the adolescent growth spurt can be determined by monitoring the growth velocity (Fig. 100-4). The spine grows heterogeneously; that is, during the adolescent growth spurt, the thoracic spine grows 1.2 cm per year and, in contrast, the lumbar spine grows 0.6 cm per year. Thus, the effect of spinal fusion on future growth can be estimated, although it should be remembered that a spine with scoliosis grows with progressive deformity. Apical vertebral growth exacerbates the deformity with further rotation, displacement, and tilting of the vertebrae.

FIGURE 100-4 Growth velocity can be plotted by measuring height gain per year. The greatest velocity and propensity for scoliosis progression occur during the adolescent growth spurt.

Predicting growth around the time of puberty is based on physical and radiographic examinations. In girls, Tanner stage 2, the development of pubic hair and breast buds, marks the onset of the growth spurt and typically precedes menarche. Skeletal age at this stage is approximately 11.5 years. The growth spurt ends at a skeletal age of 14 years, or approximately 1.5 years after menarche. For boys, Tanner stage 3, when the pubic hair becomes curly, corresponds to the onset of the growth spurts. The skeletal age is approximately 13 years and continues until 18 years. A growth rate chart is the ideal means of monitoring growth, but realistically this is not always feasible to obtain. Otherwise, the surgeon should consider physical findings such as the Tanner stage, in conjunction with historical information regarding the onset of menarche or the appearance of axillary hair in boys.

Several methods for this assessment of skeletal maturity have been reported, including Risser stage, presence of triradiate cartilage, and hand films.⁶^–¹⁰ The Risser stage is a method based on the degree of iliac ossification, with stages 1 through 4 corresponding to sequential ossification of each quarter of the iliac crest from ventral to dorsal¹¹ (Fig. 100-5). Stage 4 reflects completion of spinal growth, and stage 5 is defined as fusion to the ilium. Alternatively, hand films can be obtained for the assessment of skeletal maturity, without the need to expose the pelvis to radiation, as is required for both the Risser stage and assessment of the triradiate cartilage.^8,⁹

FIGURE 100-5 The Risser stage of iliac ossification can be used to estimate remaining maturity and growth.

The rib–vertebral angle difference (RVAD) is another measure that can guide decision making in pediatric spinal deformity. This measure is an important prognostic indicator for infantile scoliosis.¹² The RVAD is the difference between the angles formed by a line along the rib head and perpendicular to the base of the apical vertebra on the right and left sides of the spine. Spontaneous resolution of the scoliosis is expected in 85% to 90% of the cases if the RVAD is less than 20 degrees, but progression is expected with an RVAD greater than 20 degrees.¹²

Evaluation

Clinical Evaluation

Initial evaluation should begin with a detailed history, including the prenatal, birth, and cognitive and motor developmental history.⁹ Details of the suspected spinal disorder should be documented, including symptoms, deficits, onset, and progression, as well as disability and the quality of life. Past medical history can be a significant contributor, especially with congenital spinal disorders, which can be associated with other anomalies.¹³

Physical examination should include assessment of the head, entire spine, and extremities, including the skin; it should also encompass a detailed neurologic examination, including strength, tone, gait, coordination, sensation, and physiologic and pathologic reflexes. For example, neurofibromatosis may be suggested by the presence of café au lait spots or freckling, and underlying anomalies such as diplomyelia or lipomeningocele can be evidenced by patches of hair or skin dimpling. Nonambulatory patients should be examined for evidence of decubitus ulceration, which may affect surgical planning. Posture should be assessed and may include sitting, standing, and walking.

The scoliometer or inclinometer is used to quantify the rib prominence and paralumbar prominence. A scoliometer reading greater than 5 degrees is associated with a scoliosis of at least 10 degrees (Fig. 100-6).

FIGURE 100-6 Body asymmetry produced by scoliosis is assessed by noting (A) the balance of the head and trunk over the pelvis by plumb line measurements, the level of the shoulders and iliac crests, and the definition of the waist and (B) the rib rotation by scoliometer (inclinometer) measurement.

Imaging Evaluation

Initial evaluation of suspected spinal deformity often includes full-length (36-inch) posteroanterior (PA) and lateral spinal radiographs to assess global and regional spinal alignment. PA images evaluate for scoliosis, with measures including Cobb angle and coronal balance. Coronal balance is typically measured as the distance between a vertical line from the center of the C7 vertebral body (C7 plumb line) and the central sacral vertical line (CSVL) (Fig. 100-7). Lateral full-length spinal radiographs can be used to assess for regional kyphosis and lordosis and for global sagittal balance. Sagittal balance is typically measured as the distance between a vertical line from the center of the C7 plumb line and the dorsal rostral corner of the S1 vertebral body. If the C7 plumb line is ventral to the dorsal rostral corner of the S1 vertebral body, the sagittal balance measure is reflected as a positive value, and if dorsal, it is reflected as a negative value.

FIGURE 100-7 The center sacral line is the perpendicular to a horizontal line across the iliac crest, passing vertically through the sacral spinous processes. Vertebrae bisected by the center sacral line are designated as stable vertebrae.

The flexibility of scoliotic curves can be assessed with side-bending PA films to the left and to the right. Alternatively, the same information may be obtained with the patient placed over a bolster or with the use of traction. The flexibility of kyphotic deformities can be assessed with a bolster placed under the apex of the kyphosis, and the flexibility of lordotic deformities may be assessed with the spine and pelvis placed in flexion.

CT imaging provides greater detail of the bony anatomy and a three-dimensional view of complex deformities; such information may facilitate planning of surgical treatment.^14,¹⁵ CT clearly defines congenital deformities with underlying anomalies, such as hemivertebra or unsegmented bars that may be occult on plain-film radiographs (Fig. 100-8).

FIGURE 100-8 A, A 13-year-old girl presented with upper back pain and a right thoracic scoliosis. B, Due to a history of pain, a bone scan and CT scan were obtained, revealing an osteoid osteoma in the T8 pedicle.

In the setting of spinal deformity, MRI can be used to evaluate for central canal and foraminal stenosis, as well as for underlying abnormalities, which may warrant treatment or alter surgical planning. Associated abnormalities, such as tethered cord, syringomyelia, and tumors, occur in up to 15% to 38% of congenital spinal deformity patients ¹⁶^–²¹ (Fig. 100-9). Although MRI is often used as an adjunct in the imaging evaluation of pediatric spinal deformity, several specific indications necessitate this evaluation, including severe pain; neurologic findings, including motor weakness, muscle atrophy, and upper motor neuron signs; early-onset scoliosis with a Cobb angle greater than 20 degrees; atypical scoliosis curve patterns (e.g., left thoracic curves, sharp angular curves, congenital deformities, and curves that are >70 degrees); scoliosis curves with a rapid progression (>1 degree per month); neurofibromatosis; deformity associated with myelomeningocele; and lack of apical lordosis in idiopathic scoliosis^9,²² (Fig. 100-10).

FIGURE 100-9 A, A 10-year-old boy with a left thoracic curve has a normal neurologic examination. B, Because of the atypical features (male gender and left thoracic curve) an MRI scan was obtained, demonstrating syrinx.

FIGURE 100-10 Dorsal view of apical vertebrae from a left thoracic, infantile curve. The rib–vertebra angles are formed between a perpendicular to the vertebral end plates and a line along the corresponding rib head. The rib–vertebral angle difference (RVAD) is calculated by subtracting the convex angle (a) from the concave angle (b): RVAD = b−a.

Idiopathic Scoliosis: Early Onset and Adolescent Onset

Idiopathic scoliosis has a familial tendency and a bimodal frequency distribution. With the early-onset type the majority of cases occur in infancy and a second major peak arises during adolescence. Idiopathic scoliosis is divided into two groups: early onset (<5 years) and late onset (5 years to skeletal maturity).^23,²⁴ The most common type is adolescent idiopathic scoliosis (AIS).

The diagnosis of AIS is one of exclusion. In idiopathic scoliosis, deformity is the most common reason for referral. Occasionally, low-grade, activity-related back pain can result from lumbar curves or curves greater than 40 degrees. Atypical cases demand further evaluation to establish a diagnosis.^9,²²

The prevalence of AIS with a curve of at least 10 degrees is 2% to 3% of the adolescent population. Curves in excess of 20 degrees have a prevalence of 0.3% to 0.5%, whereas the prevalence of curves in excess of 40 degrees is 0.1%.

Curves originating before the age of 5 years can exceed 100 degrees and affect both the cardiac and pulmonary systems. Thus, treatments are predicated by patient age and degree of deformity.

Adolescent Idiopathic Scoliosis

Clinical Features

AIS occurs more frequently in girls than in boys. The typical curve pattern is a right thoracic curve with a compensatory left lumbar curve. Patients typically present with physical deformity from body asymmetry, such as a trunk shift, unlevel shoulders, rib prominence, and breast or waist asymmetry. Screening has traditionally been a means of identifying these curves; however, there is no evidence that this has changed clinical outcomes.

The natural history of AIS was studied thoroughly by Weinstein, who followed a cohort of patients for over 40 years, and by Collis and Ponseti.²⁵^–²⁸ Factors that correlate with progression of idiopathic curves include physiologic younger age, female gender, curve magnitude, and double curves. During the adolescent years, curves typically progress an average of 1 degree per month and curves in excess of 50 degrees have a high risk of progression even after skeletal maturity. Finally, there is a significant inverse relationship between the pulmonary vital capacity and magnitude of thoracic scoliosis. Thoracic curves greater than 70 degrees are associated with a vital capacity less than predicted for size.

Classification

Lenke et al. developed the currently most commonly applied classification for AIS.^29,³⁰ Based on both coronal and sagittal radiographs, it was developed to aid in determination of the appropriate vertebral levels to be included in an arthrodesis. The classification system includes six curve types (numbered 1 through 6), a lumbar spine modifier (A, B, or C) that is based on deviation of the apical lumbar vertebra, and a sagittal plane modifier (−, N, or +).

The structural curve types are main thoracic (type 1), double thoracic (type 2), double major (type 3), triple major (type 4), thoracolumbar/lumbar (type 5), and thoracolumbar/lumbar main thoracic (type 6). The left and right side-bending radiographs determine which curves are structural and nonstructural. The lumbar spine modifier is determined on the basis of the relationship of the center CSVL to the lumbar curve on the coronal radiograph. The lumbar modifiers quantify the amount of lumbar curve as A (minimal), B (moderate), and C (large). The CSVL either (A) runs through the lumbar vertebra to the stable vertebrae, (B) runs between the medial border of the lumbar concave pedicle and the concave lateral margin of the apical vertebrae, or (C) falls completely medial to the entire concave lateral aspect of the apical vertebrae. The sagittal thoracic modifier describes overall thoracic kyphosis: hypokyphosis (−), a curve less than +10 degrees; normal (N), a curve +10 to +40 degrees; or hyperkyphosis (+), a curve more than +40 degrees.