Chapter 100 Pediatric Spinal Deformities and Deformity Correction
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.)
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.
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
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).
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.
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).
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 patients16–21 (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 scoliosis9,22 (Fig. 100-10).
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
Adolescent Idiopathic Scoliosis
Clinical Features
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 +).
Treatment
Bracing may be indicated in patients with AIS for curves greater than 20 degrees that have progressed more than 5 degrees. Adolescents with significant remaining growth potential who have curves between 25 degrees and 40 degrees may also warrant bracing, despite no documented progression.31 Bracing is typically stopped in adolescents if the curve progresses to surgical dimensions (45–50 degrees) or when skeletal maturity is reached.
Surgery for AIS is often recommended in growing children once curves reach 45 degrees. Surgery is also recommended for skeletally mature teenagers for curves greater than 50 degrees, because curves of this severity have a high risk of progression in adult life.25,26,32 The goals of surgery include stopping curve progression, restoring alignment, balancing the spine in all anatomic planes, and minimizing the number of vertebral levels that are fused (Figs. 100-11 to 100-13). Current dorsal instrumentation systems include hooks, wires, and/or pedicle screws that are typically connected with dual rods (Figs. 100-14 to 100-16). Pedicle screw instrumentation of pediatric patients in experienced hands has been shown to be safe.33–37 Regardless of the instrumented system selected, the ultimate success of the procedure depends on achieving solid bony fusion.
