Thoracolumbar Spinal Disorders in Pediatric Patients

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CHAPTER 223 Thoracolumbar Spinal Disorders in Pediatric Patients*

Justin S. Smith, Christopher I. Shaffrey

Disorders of the pediatric thoracolumbar spine include a remarkably diverse range of conditions arising from congenital, developmental, and acquired pathologies (Table 223-1). In distinct contrast to adult spinal disorders, pediatric spinal disorders are not typically related to the degenerative aging process. Parallel contrasts in the management of pediatric and adult spinal disorders also exist, not only because of the differing common pathologies but also because of the growth potential of the immature spine and the long-term functional expectations. Effective care of pediatric patients with spinal disorders requires an understanding of the pathologies encountered, the means by which these patients are clinically evaluated, and the strategies, both nonoperative and operative, by which these patients are managed. Toward this end, this chapter provides a basic overview of thoracolumbar spinal disorders of the pediatric spine.

TABLE 223-1 Causes of Pediatric Thoracolumbar Spinal Disorders

Idiopathic scoliosis

Infantile (<3 years old)

Juvenile (3 to 9 years old)

Adolescent (10 years old to skeletal maturity)

Modified from Smith JS, Abel MF, Shaffrey CI, et al. Decision making in pediatric spinal deformity. Neurosurgery. 2008;63(3 suppl):54-68.

Clinical Evaluation of Pediatric Spine Patients

Initial evaluation of a pediatric patient with a suspected spinal condition should begin with a complete history, including the prenatal and birth history, as well as the cognitive and motor developmental history.¹ Details with regard to the suspected spinal disorder should be documented, including symptoms, deficits, and the time course over which they have developed and progressed. In addition, attention should be directed to the degree to which the symptoms, deficits, and deformity have had an impact on the ability to function and the quality of life of the patient. The past medical history and current medical concerns should be carefully reviewed because it is not uncommon for pediatric spinal disorders, especially congenital spinal disorders, to be accompanied by other anomalies that may warrant further investigation. For example, anatomic and physiologic abnormalities of the renal, respiratory, and cardiac systems may be associated with congenital spinal disorders.²

Physical examination of a pediatric patient with a suspected spinal disorder should include not only specific assessment of the suspected spinal condition but also assessment for other associated conditions. The examination should consist of a general assessment of the head, entire spine, and extremities, including the skin. Neurofibromatosis may be suggested by the presence of café au lait spots or freckling, and underlying anomalies such as diplomyelia or lipomeningocele may be suggested by patches of hair or midline dimpling. The skin and pressure points of nonambulatory patients should be examined for evidence of decubitus ulceration, which may have an impact on surgical planning. Palpation of the entire spine can be performed to help define areas of tenderness and deformity. An assessment of posture should be made and may include sitting, standing, and walking. Adam’s forward bend test may be used to assess for prominence of a rib or transverse process. The physical examination should also include at least a general neurological assessment, including motor strength, muscle tone, gait, coordination, and sensory evaluation, as well testing for the presence of physiologic and pathologic reflexes.

Imaging Evaluation of Pediatric Spine Patients

Imaging studies are invaluable in the evaluation of spinal disorders, and selection of the appropriate studies should be guided by the patient’s history and physical examination, as well as by the suspected pathology. Initial evaluation of a patient with a suspected spinal deformity often includes full-length (36-inch) posteroanterior (PA) and lateral spine radiographs to provide assessment of global and regional spinal alignment. For patients able to stand, these radiographs should be obtained in a standing position, and care should be taken to ensure that the legs are straight, specifically that the knees are not bent and the hips are not flexed. PA images may be used to assess for scoliosis, with measures including Cobb’s angle and coronal balance. Coronal balance is typically measured as the distance between a line dropped vertically from the center of the C7 vertebral body (C7 plumb line) and the central sacral vertical line (CSVL) (Fig. 223-1A). With the PA image in a true-left/true-right orientation, displacements of the C7 plumb line to the left of the CSVL are reflected as negative values, and displacements to the right of the CSVL are reflected as positive values. 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 line dropped vertically from the center of the C7 vertebral body (C7 plumb line) and the posterior superior corner of the S1 vertebral body (Fig. 223-1B). If the C7 plumb line is anterior to the posterior superior corner of the S1 vertebral body, the sagittal balance measure is reflected as a positive value, and if posterior, it is reflected as a negative value. Radiographic assessment of suspected spinal deformity should include both PA and lateral views because kyphotic deformities, such as those associated with neuromuscular disorders, may also be accompanied by a scoliotic deformity and primary scoliotic deformities may also include a degree of kyphotic deformity.

FIGURE 223-1 Full-length standing spinal radiographs in a 12-year, 7-month-old girl with idiopathic scoliosis (double major), including posteroanterior (A), lateral (B), and left (C) and right (D) side-bending views. A, The long and short vertical lines are the C7 plumb line and the central sacral vertical line, respectively. The distance between these lines (dashed horizontal line) is the coronal balance. B, The long and short vertical lines indicate the C7 plumb line and the posterior superior corner of the S1 vertebral body, respectively. The distance between these lines (dashed horizontal line) is the sagittal balance. C and D, The lumbar and thoracic curves are shown to be relatively flexible.

For patients with spinal deformity, radiographic imaging may also be beneficial in assessing the flexibility of deformities, which may prove useful for surgical planning. For example, the flexibility of scoliotic curves may be assessed with full-length PA supine radiographs in which the patient bends to the left side and to the right side (Fig. 223-1C and D). For patients who are not able to adequately cooperate with side-bending films, curve flexibility may be assessed with the patient placed over a bolster or with the use of traction. Similarly, the flexibility of kyphotic deformities may 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.

Computed tomography (CT) can provide greater detail of bone anatomy and, with reformatted multiplanar images, can provide a three-dimensional view of complex deformities.^3,⁴ Congenital deformities may have underlying anomalies, such as a hemivertebra or unsegmented bars, that may not be readily discernible on plain radiographs but can often be clearly defined with CT. The dimensions of the bony anatomy, such as pedicles and vertebral bodies, are also best assessed with CT, and such information may facilitate planning of surgical treatment, including selection and placement of implants.

Magnetic resonance imaging (MRI) is commonly used for the assessment of suspected pediatric spinal conditions. In the setting of spinal deformity, MRI can be used to evaluate for canal and foraminal stenosis, as well as for underlying abnormalities that may warrant treatment or affect surgical planning. For example, intraspinal deformities, such as tethered cord, syringomyelia, and tumors, have been reported in 15% to 38% of patients with congenital spinal deformity.⁵^–¹⁰ Although MRI is often incorporated into the imaging evaluation of pediatric spinal deformity, certain findings should prompt special consideration for such evaluation. These findings include (1) pain that is severe; (2) neurological abnormalities, including motor weakness, muscle atrophy, and upper motoneuron signs; (3) early-onset scoliosis with a Cobb angle greater than 20 degrees; (4) atypical scoliosis curve patterns, such as left thoracic curves, sharp angular curves, congenital deformities, and curves greater than 70 degrees; (5) scoliosis curves with rapid progression (>1 degree per month); (6) neurofibromatosis patients to evaluate for an underlying neoplastic process; (7) deformity in the setting of myelomeningocele; and (8) absence of apical lordosis in patients with idiopathic scoliosis.^1,¹¹

Progression of deformity in the pediatric spine is typically related to the degree of skeletal maturity, with greater remaining growth potential corresponding to a greater risk for progression of deformity. Thus, assessment of skeletal maturity can provide prognostic information. Several methods for this assessment have been reported, including the Risser stage, closure of the triradiate cartilage, and hand films.^1,¹²^–¹⁵ The Risser stage reflects the degree of iliac ossification and is based on the proportion of the iliac crest that has undergone ossification. The Risser stage has been used historically to estimate skeletal maturity and remaining growth potential, with stages 1 through 4 corresponding to sequential ossification of each quarter of the iliac crest from anterior to posterior.¹⁶ Once stage 4 is reached, spinal growth is generally considered to be complete. Closure of the triradiate cartilage of the pelvis has also been correlated with the completion of spinal growth. Alternatively, hand films can be obtained for assessment of skeletal maturity without the need to expose the pelvis to radiation, as required for both the Risser stage and assessment of the triradiate cartilage.^1,¹⁴

The rib-vertebral angle difference (RVAD) of Mehta is another example of an imaging study that can affect decision making in pediatric spinal deformity. This measure is an important prognostic indicator for infantile scoliosis.¹⁷ The RVAD is the difference between the angles formed by a line along the rib head and a 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 patients if the RVAD is less than 20 degrees, whereas an RVAD of greater than 20 degrees suggests a high likelihood of curve progression.¹⁷

Congenital Disorders

Because of the complexity of embryogenesis, a broad range of congenital spinal disorders can develop.¹⁸ Although many congenital spinal disorders may not be evident at birth, each is thought to result from errors that occur during embryogenesis.¹⁹ Congenital spinal anomalies most commonly occur as sporadic events and are relatively uncommon, with an incidence of approximately 1 per 1000 to 2000 individuals in the general population.²⁰^–²² However, not all congenital spinal disorders are sporadic. For example, spinal dysraphism occurs in approximately 0.1% to 0.2% of individuals in North America, but the incidence in subsequent offspring increases to 2.5%,²³ thus suggesting environmental, genetic, epigenetic, or other factors.

Congenital spinal malformations are not infrequently accompanied by other congenital anomalies, with the most common organ systems affected being those developing at a similar phase of embryogenesis. The urologic system is the most common system affected, with a reported incidence of up to 25%.²⁴ The cardiovascular system demonstrates anomalies, including ventricular septal defects, atrial septal defects, dextrocardia, and the tetralogy of Fallot, in up to 10% of patients. Basu and colleagues evaluated 126 consecutive patients with congenital spinal deformity for evidence of intraspinal anomalies, as well as for defects in other organ systems.⁵ More than a third (37%) of the patients were found to have intraspinal abnormalities, and more than half (55%) were found to have other organic defects, including cardiac defects in 26% and urogenital abnormalities in 21%.

Congenital Scoliosis

Scoliosis is an abnormal curvature of the spine in the coronal plane. Congenital scoliosis is distinguished by the presence of anomalous vertebrae at birth (Fig. 223-2). Although the vertebral abnormality is present at birth, typically no evidence of deformity is noted until the growth phases of childhood or adolescence. Relatively balanced spinal anomalies may even go undetected until adulthood or only be found incidentally. Infantile idiopathic scoliosis and juvenile idiopathic scoliosis are also manifested as scoliosis in childhood, but these types are distinguished from congenital scoliosis by their lack of vertebral anomalies.²⁵

FIGURE 223-2 Radiographs of a 6-year, 7-month-old boy with congenital scoliosis, including preoperative posteroanterior (A) and lateral (B) radiographs, computed tomographic reconstructions showing an L2 hemivertebral anomaly (C and D), and postoperative posteroanterior (E) and lateral (F) radiographs, 1 year after resection of the vertebral anomaly (anterior approach) and unilateral posterior instrumented arthrodesis from L1 to L3.

The clinical findings in patients with congenital scoliosis are highly varied and depend on the type and vertebral level of the spinal anomaly, the number of anomalies, and the degree to which the anomalies result in either cumulative global balance or imbalance. At the extremes, the anomalies can result in rapidly progressive scoliosis with significant morbidity in early childhood or can result in minimal or no deformity throughout life. Approximately a quarter of patients with congenital scoliosis can be expected to not progress, approximately half progress slowly, and the remaining quarter progress rapidly.¹⁸ With advancements in CT and MRI have come improvements in the ability to classify congenital scolioses, as well as improvements in the ability to optimize the planning and timing of therapeutic management.

The normal vertebral body has growth plates on the superior and inferior surfaces, and normal spine growth occurs as a balanced process between these plates. Congenital spinal anomalies can result in absent or deficient growth at one or more end plates and may affect the vertebral level asymmetrically and result in unbalanced growth. Lateral asymmetry of growth can produce scoliosis, anterior-posterior asymmetry of growth can result in a kyphotic or lordotic deformity, and combinations of asymmetric growth can produce kyphoscoliosis or lordoscoliosis.

Congenital abnormalities of the spine are classified according to the embryologic development of the spine, with categories including failure of formation, failure of segmentation, and mixed anomalies.^1,²⁶ Failure of formation ranges from mild wedging to complete absence of a vertebra. The most common cause of congenital scoliosis is a hemivertebra, which typically consists of a wedged vertebral body with a single pedicle and hemilamina. Segmentation failure results in unilateral or bilateral fusion of vertebrae.^27,²⁸ A unilateral unsegmented bar, which consists of a bony block that includes the disk space and facet joints, is the most common segmentation failure. Among the various complex combinations of vertebral anomalies that can coexist is an unsegmented bar with a contralateral hemivertebra, which can result in severe progressive scoliosis.²⁹

The degree to which hemivertebrae result in spinal deformity is based on multiple factors, including the vertebral level and degree of segmentation. A hemivertebra located at the thoracolumbar or lumbosacral junction can produce substantial deformity. Segmentation refers to the extent of normal disk formation above and below the vertebral body. A fully segmented hemivertebra has a normal disk space at the superior and inferior end plates, thereby allowing nearly normal longitudinal growth. This nearly normal capacity for unilateral growth, coupled with the lack of growth capacity on the contralateral side, can result in significant deformity. A semisegmented vertebra lacks a disk space at either the superior or inferior end plate. This would be expected to produce relatively balanced growth, although lateral differences in growth may still exist and can result in some degree of scoliosis. A nonsegmented vertebra lacks adjacent disk spaces and is fused to the adjacent vertebrae. Although the wedge shape of a nonsegmented vertebra can produce some degree of deformity, it is typically not progressive.

Unilateral unsegmented bars resulting from failure of segmentation of two or more vertebrae are another common cause of congenital scoliosis. Because unilateral unsegmented bars contain no growth plate, there is assymetric, unbalanced growth from the contralateral growth plate, which can result in the potential for deformity.

An understanding of the natural history of congenital spinal anomalies is important to define the optimal treatment strategies. McMaster and Ohtsuka reported a series of 202 patients with congenital scoliosis and noted that 11% did not progress, 14% had limited progression, and 75% progressed significantly.²⁵ The type of anomaly is an important factor with regard to progression. The most severe congenital scoliosis may result from a unilateral unsegmented bar with a contralateral hemivertebra at the same level. The significant potential for this combination of anomalies to produce deformity argues in favor of treating the patient immediately without allowing a period of observation.^25,³⁰ Patient age is also an important factor in determining the capacity for progression of deformity, with the greatest risk typically occurring during the preadolescent growth spurt. Children in whom the deformity develops in the first years of life often have considerable growth imbalance and are at high risk for significant deformity.

In children with severe or progressive congenital scoliosis, surgery is frequently the most effective treatment. Surgical options include hemivertebra excision, convex hemiepiphysiodesis, fusion in situ, spinal instrumentation, and thoracoplasty with a vertical expansion prosthetic titanium rib (VEPTR).¹⁸ Hemivertebra excision offers the ability to directly address the biomechanical decompensation and can provide immediate and often significant correction of the deformity.³¹^–³³ Convex hemiepiphysiodesis involves excision of the disk and fusion on the convex side of the curve and relies on the remaining growth potential on the side of the concavity.³⁴ Although fusion in situ with casting or a brace has historically been popular, the use of posterior instrumented arthrodesis has become more popular in those requiring fusion. Patients with progressive curves and congenital rib fusions may benefit from thoracoplasty with a VEPTR.^35,³⁶ It is important to recognize the surgical morbidity that can accompany complex reconstructions for congenital scoliosis. Reames and coauthors reported a modern series of more than 2000 patients from the Scoliosis Research Society treated for congenital scoliosis; the morbidity rate was higher than 10% and mortality was 0.3%.³⁷

Congenital Kyphosis

Congenital kyphosis is a deformity in the sagittal plane that results from vertebral anomalies, including failure of formation and segmentation (Fig. 223-3).¹ Left untreated, congenital kyphosis often results in neurological deficits. Winter and colleagues reported a classification system for congenital kyphosis in which three types are distinguished: failure of formation of the vertebral body (type I), failure of segmentation of the vertebral body with a ventral unsegmented bar (type II), and mixed failure of formation and segmentation (type III).³⁸ The most common form, type I, is also the most common type to result in severe deformity and neurological deficits, with the severity of deformity being related to the magnitude of the failure of formation. Type II produces less deformity and is considerably less likely to result in a neurological deficit. The severity of kyphosis produced with type II depends on the difference between ventral vertebral growth and growth of the dorsal structures. Type III is very rare and is thought to behave in a similar fashion as type I.

FIGURE 223-3 Radiographs of a 24-year-old woman with congenital kyphosis, including preoperative posteroanterior (A) and lateral (B) radiographs, computed tomographic reconstruction images demonstrating a T11 hemivertebra with 80 degrees of thoracic kyphosis (C, D, and E are left-lateral, midline, and right-lateral sagittal CT reconstructions, respectively), and postoperative posteroanterior (F) and lateral (G) radiographs, 1 year after T10 and T11 vertebral column resection, cage placement, and posterior instrumented arthrodesis from T7 to L2.

In general, nonoperative treatment is not recommended for congenital kyphosis because of the significant potential for the development of neurological deficits with progression. Generally, posterior fusion alone is adequate in patients who are younger than 5 years and have less than 55 degrees of kyphosis. Combined anterior and posterior procedures are often required in older patients and in those with greater than 55 degrees of kyphosis. Substantial risks for morbidity and mortality can be associated with surgical correction of congenital kyphosis. Kim and coauthors reported that complications are more likely to occur in the setting of kyphosis greater than 60 degrees and in patients in whom preoperative imaging demonstrates cord compression.³⁹

Congenital Lordosis

Congenital lordosis results from dorsal defects in segmentation and is considerably rarer than either congenital scoliosis or congenital kyphosis.⁴⁰ Congenital lordosis is often accompanied by a deformity in the coronal plane (lordoscoliosis) that results from a dorsolateral location of the unsegmented bar. The incidence of neurological deficits in patients with congenital lordosis is substantially lower than that in patients with congenital kyphosis. Instead, the most significant complications of congenital lordosis often relate to impairment of pulmonary function when the deformity occurs in the thoracic region.

Congenital Stenosis

Congenital spinal stenosis is considerably less common than the degenerative spinal stenosis that afflicts the adult population, although the congenital abnormality may remain essentially asymptomatic until adulthood. Congenital spinal stenosis is distinguished from developmental spinal stenosis by the latter usually occurring in conjunction with conditions such as achondroplasia, hypochondroplasia, diastrophic dwarfism, Morquio’s syndrome, and hereditary multiple exostoses.¹⁸ Verbiest has described three types of congenital spinal stenosis.⁴¹^–⁴³ The first type occurs together with a spinal dysraphism. The symptoms typically reflect a combination of the two conditions, and it is not uncommon for severe radicular symptoms and deficits to occur.

Verbiest’s second type of congenital spinal stenosis occurs as a result of failure of vertebral segmentation.⁴¹^–⁴³ A reduced midsagittal diameter of the vertebral canal frequently occurs in the area of the block vertebrae. The signs and symptoms are similar to those observed with idiopathic developmental spinal stenosis.

Verbiest’s third type of congenital stenosis results in an intermittent stenosis syndrome (d’Anquin’s syndrome).⁴¹^–⁴³ In this type, the spinous process of S1 is absent, and a central cleft exists in the S1 lamina. A hook-like process of L5 may protrude through this cleft when the patient assumes a standing posture and result in reduction of the midsagittal diameter of the sacral canal. Thus, the patient experiences radicular symptoms with standing and walking that are relieved with sitting.

Dysplastic Spondylolisthesis

Spondylolisthesis is slippage of one vertebral body relative to an adjacent level. The classification of spondylolisthesis by Wiltse and coworkers is the most widely accepted. They described five types of spondylolisthesis, including dysplastic (type I), isthmic (type II), degenerative (type III), traumatic (type IV), and pathologic (type V).⁴⁴ Dysplastic spondylolisthesis is congenital and results from a defect in the facet complex, typically L5-S1, that permits listhesis (Fig. 223-4). The development of spondylolisthesis is extremely rare in infancy and typically does not occur until the onset of ambulation.

FIGURE 223-4 Radiographs of a 15-year, 6-month-old boy with L5 spina bifida occulta and grade IV L5-S1 dysplastic spondylolisthesis, including preoperative posteroanterior (A) and lateral (B) radiographs, a sagittally reconstructed computed tomographic image (C), a T2-weighted sagittal magnetic resonance image (D), and postoperative posteroanterior (E) and lateral (F) radiographs after partial reduction of the spondylolisthesis and instrumented arthrodesis from L4 to S1.

In patients with dysplastic spondylolisthesis, the dysplastic facet joints may have an axial or sagittal plane orientation. A horizontal orientation with axial dysplasia is more commonly seen in the setting of spina bifida. In contrast, the neural arch is often intact with sagittal dysplasia. The clinical findings are often similar for dysplastic spondylolisthesis related to axial and sagittal dysplasia and may include back or leg pain, paresthesias, weakness, and rarely bowel or bladder incontinence. In general, higher grade slips are more likely to be accompanied by a neurological deficit. Patients with axial dysplasia and associated spina bifida are at increased risk for high-grade spondylolisthesis. Younger patients with skeletally immature spines are at higher risk for progression of the slippage.

The initial treatment of dysplastic spondylolisthesis should typically be nonoperative, except in the setting of documented progression in a young patient or slippage of greater than 50% at initial evaluation. Surgical treatment may include decompression with fusion in situ or decompression, fixation with pedicle screws, and fusion. Instrumentation may offer the ability to provide partial or complete reduction, but caution should be exercised because reduction is associated with a higher rate of development of new neurological deficits.⁴⁵

Spinal Dysraphism

Spinal dysraphism is caused by abnormalities in spinal cord and column development, with associated malformations resulting from failure of normal embryologic structures to fuse in the midline. Dysraphisms have been broadly group into spina bifida aperta and spina bifida occulta. Spina bifida aperta includes lesions that are either open or have the potential to open at birth and include myelomeningocele, meningocele, and myelodysplasia. The malformations of spina bifida occulta are covered by complete layers of dermis and epidermis and are not readily apparent. Examples include lipomyelomeningocele, neurenteric cyst, lipoma, dermoid cyst, dermal sinus tract, tethered cord, and diastematomyelia.

The incidence of neural tube defects in the United States is approximately 0.6 per 1000 live births, but worldwide the incidence varies and is as high as 8.7 per 1000 live births in Northern Ireland.^23,⁴⁶ Several environmental factors have been associated with spinal dysraphism, including maternal hyperthermia; maternal deficiencies of folate, calcium, vitamin C, and zinc; and either deficient or excess amounts of vitamin A.^18,^23,⁴⁶

During embryogenesis, the skin is separated from the neural tube by a layer of mesoderm. If the ectoderm is incompletely separated from the neural tube, the resulting defects may include cord tethering, diastematomyelia, or a dermal sinus. If the ectoderm separates from the neural tube prematurely, mesenchymal tissues may be incorporated between the neural tube and skin and result in the development of lesions such as lipomas. If the neural tube does not fuse properly, midline spinal effects may occur, such as myelomeningoceles.

Spina bifida occulta is often not readily apparent on the skin surface. However, a variety of cutaneous stigmata may hint at an underlying defect, including dimples, a wayward gluteal fold, hairy skin patches, dermal sinuses, capillary hemangiomas, and palpable masses that may represent subcutaneous lipomas.¹⁸

Early surgical closure is typically indicated for cases of spina bifida aperta to reduce the risk for local infection and potentially meningitis. Certain types of spina bifida occulta may require surgical treatment, including dermal sinus tracts and cord tethering.

Diastematomyelia

Diastematomyelia is a split cord anomaly in which there are two hemicords, separated by a cartilaginous or bony septum, and the two hemicords are contained in separate dural sacs.⁴⁷^–⁵⁰ Hood and coauthors reported a series of 60 patients with diastematomyelia, with approximately half of the cases occurring at the thoracic level and half at the lumbar level.⁴⁸ Diastematomyelia should be distinguished from diplomyelia, another split cord anomaly in which two separate cords are contained in one dural sac without an intervening cartilaginous or bony septum.

Pang and associates proposed a unified theory of split cord malformations (SCMs).⁵¹ Two types of SCMs were proposed in this report, including type I SCMs, which have two hemicords, each in separate dural tubes and intervening osseocartilaginous septum, and type II SCMs, which have two hemicords in a single dural tube that may be separated by a nonrigid, fibrous septum. In the SCM unified theory, both types of SCMs arise from one embryologic error at the time of neural closure, but the phenotype depends on further stages of spinal column/cord development. In the report by Pang and colleagues, there were a series of 39 cases that included 19 type I, 18 type II, and 2 composite SCMs in tandem.⁵¹

Epidermoids, Dermoids, and Dermal Sinus Tracts

Dermoids and epidermoids are relatively rare spinal tumors that account for approximately 1% to 2% of all spinal tumors.^24,⁵² These lesions may occur in isolation or in conjunction with a dermal sinus. When occurring in isolation, these lesions may cause symptoms and deficits from neurological compression or may be manifested as acute chemical meningitis secondary to cyst rupture and spillage of cholesterol crystals into cerebrospinal fluid (CSF). Dermoids and epidermoids may occur in the thoracic, lumbar, and sacral spine, with a slightly higher prevalence at more cephalad levels.

Dermal sinus tracts are lined with squamous epithelium and typically extend from the skin surface to the spinal canal. They occur in approximately 1 in every 1500 births and may be present at any spinal level, from the occiput to the sacrum. In approximately half of dermal sinus tracts, dermoid or epidermoid tumors arise within the tract.

Dermal sinus tracts and dermoids are thought to be caused by incomplete dysjunction of ectoderm from endoderm during the fourth week of embryogenesis. As the spinal cord ascends in the spinal canal during development, the tract may become elongated and stretch over several spinal levels. The appearance of these tracts at the skin surface is subtle, and they may be missed until closer inspection is prompted by recurrent episodes of meningitis, frequently caused by Staphylococcus aureus. Once identified, dermal sinus tracts should be treated definitively by complete surgical excision.

Tethered Cord

Classically, the diagnosis of tethered cord required the presence of a low-lying conus medullaris, typically caused by a short and thickened filum terminale, the origin of which remains unclear. This definition has been expanded to include any tethering of the spinal cord by fibrous bands or adhesions or by an intradural lipoma.

Tethered cord syndrome describes the neurological symptoms and deficits that can accompany spinal cord tethering. These findings are thought to arise from hypoxic stress with vascular insufficiency in the stretched spinal cord and include pain, bladder dysfunction, leg weakness with atrophy of the calf muscles, loss of deep tendon reflexes, and loss of sensation in a dermatomal pattern.^53,⁵⁴ Surgical treatment typically includes spinal cord detethering.⁵⁵

Neuromuscular Disorders

Both scoliosis and sagittal plane deformities are common in patients with primary disorders of the nervous system, muscular system, or both, probably related to abnormal spine growth. The Scoliosis Research Society has provided a classification system of neuromuscular scoliosis that includes categories of upper motoneuron pathology (e.g., cerebral palsy, Rhett’s syndrome), lower motoneuron and mixed pathology (e.g., Charcot-Marie-Tooth disease, spinal muscular atrophy, spinal cord injury, myelomeningocele), and primary muscle disease (e.g., Duchenne’s muscular dystrophy, myopathies).⁵⁶

The likelihood of deformity developing depends on the severity of the underlying disorder. For example, in nearly all patients with Duchenne’s muscular dystrophy, collapsing deformity develops as the disease progresses and ultimately requires surgical treatment, typically after the patient becomes nonambulatory. Scoliosis develops in up to 70% of patients with severe cerebral palsy, often by the age of 7 years.^57,⁵⁸ Among patients with myelomeningocele at L3 or above, significant deformity develops in at least 70%. By the time that these deformities develop, many of these patients are nonambulatory and may suffer from significant comorbidity, including osteopenia, pulmonary disease, and nutritional deficiencies.

Nonoperative treatment of neuromuscular deformities includes bracing and customized wheelchair seating systems that provide support for the head, trunk, pelvis, and extremities. Although several studies suggest that bracing typically does not prevent deformity,⁵⁹^–⁶⁴ it can provide support for young children and for patients with flexible spines (e.g., hypotonic myopathy, some types of cerebral palsy, spina bifida, and spinal muscular atrophy).

When contemplating surgical treatment of neuromuscular deformities, it is imperative to be clear with the patient and caregivers of the goals of the treatment and what the realistic expectations should be. Typical goals of surgery may include improvement of quality of life through alleviation of pain, improvement of sitting balance, stabilization of pulmonary function, improvement of gastrointestinal function, prevention of progression of the deformity, and lessening of caregiver burden.

Neuromuscular curves are often sweeping and involve significant portions of the spine. The threshold for surgical treatment is not precisely defined, but typically curves greater than 50 degrees are considered for surgical treatment. Because this magnitude may be reached while the spine is considerably immature, bracing may be used to delay surgical treatment if the curve remains flexible. In certain circumstances it may be warranted to fuse curves that are less than 50 degrees. For example, with muscle diseases such as muscular dystrophy, it may necessary to fuse curves less than 50 degrees before pulmonary function declines to the point that surgery may not be tolerated. The nonambulatory status and often severe comorbidities of the neuromuscular deformity population result in significant morbidity and mortality being associated with surgical correction. Reames and coauthors reported a series of 4657 patients with neuromuscular scoliosis who underwent surgical correction by the membership of the Scoliosis Research Society. The overall morbidity and mortality rates were 18% and 0.3%, respectively.³⁷

Cerebral Palsy

In nonambulatory cerebral palsy patients, scoliosis develops in approximately 70% and often by the age of 15 years (Fig. 223-5).⁵⁸ Although these curves can progress even into adulthood, the greatest progression typically occurs during the growth years (≈2 to 4 degrees per month).^65,⁶⁶ These deformities are usually long sweeping curves that often include pelvic obliquity and may be accompanied by a significant degree of kyphosis or hyperlordosis. Although braces may be used to temporize, many of these patients ultimately reach the point of surgical consideration.⁶⁴ Surgical correction frequently includes long segmental instrumentation with pelvic fixation. In general, significant pelvic and hip contractures should be treated before surgery because pelvic fixation may otherwise exacerbate these conditions.

FIGURE 223-5 Radiographs of an 11-year, 4-month-old boy with cerebral palsy and neuromuscular scoliosis, including preoperative posteroanterior radiographs without a brace (A), in a brace (B), and in traction (C), as well as a lateral radiograph (D). Also shown are postoperative posteroanterior (E) and lateral (F) radiographs 21 months after instrumented arthrodesis from T3 to S1 and the placement of iliac bolts.

Neuromuscular Dystrophies and Myopathies

Several muscular dystrophies and myopathies are associated with the development of spinal deformity. Surgical treatment typically includes fusion with segmental instrumentation and is extended to the pelvis for pelvic obliquity of greater than 15 degrees. Patients with muscle diseases may be more prone to malignant hyperthermia when exposed to anesthetic agents. Only nondepolarizing agents should be used if muscle blockade is necessary for surgery. It is important to properly evaluate cardiac and pulmonary function in this group of patients. Restrictive lung disease from spinal deformity, coupled with decreased muscle function, can produce significant pulmonary compromise. Although complication rates climb considerably when vital capacity falls below 40% of predicted, successful surgery may still be possible if it is recognized that the patient may require a tracheostomy for long-term ventilation.⁶⁷^–⁷⁰ Pulmonary function is not likely to improve with correction of the deformity, but it may slow its progression.⁷¹ Preoperative assessment of cardiac function is important in patients with neuromuscular deformity, especially those with Duchenne’s muscular dystrophy and myotonic dystrophy. Notably, for the most common muscular dystrophy, Duchenne’s, steroid treatment offers the potential to prolong ambulation and delay the onset of scoliosis.⁷²

Myelomeningocele

Spinal deformity frequently develops in patients with myelomeningocele (Fig. 223-6). The more cephalad the last level of neurological function, the more likely that spinal deformity will develop. More than 70% of patients who have the lowest level of neurological function at L3 or above will have signs of deformity. There are many special considerations for patients with myelomeningocele when contemplating surgical correction of spinal deformity.⁵² Many of these patients have absent lamina or other posterior elements or have dysplastic posterior elements, including pedicles. This reduces the bony elements available for fusion and may necessitate anterior diskectomies and pedicle screw fixation. Many of these patients have poor skin quality or scarring over their spinal defect, which may require preoperative placement of tissue expanders and a collaborative approach with a plastic surgeon. Chiari malformations and cord tethering are not uncommonly present in these patients, and CSF flow and spasticity may be exacerbated by spinal instrumentation. In general, tethered cord and Chiari malformation should be addressed in these patients before spinal fusion. Many of these patients have severe thoracolumbar or lumbar kyphosis or a gibbous deformity that may require resection of the spinal column.

FIGURE 223-6 Radiographs of a 12-year, 8-month-old girl with myelomeningocele and neuromuscular scoliosis, including preoperative posteroanterior (A) and lateral (B) sitting radiographs, posteroanterior (C) and lateral (D) radiographs in traction, and postoperative posteroanterior (E) and lateral (F) radiographs, 14 months after instrumented arthrodesis from T2 to S1 with pelvic fixation. Note the use of Dunn-McCarthy rods for sacral fixation.

Pelvic fixation is frequently required in patients with myelomeningocele who undergo surgery for spinal deformity; however, the iliac wings are often not wide enough to hold iliac screws. Alternatively, Dunn-McCarthy rods may be used with contouring of the rods into an S configuration such that the lower limb passes through the S1 foramen or over the sacral ala to sit in front of the sacrum. Myelomeningocele patients commonly exhibit kyphotic deformity, and the use of Dunn-McCarthy rods is well suited to providing correction.

Spinal Cord Injury and Paralytic Deformity

Remarkably, a paralytic spinal deformity will develop in more than 98% of skeletally immature children with a spinal cord injury, and more than 50% will be treated surgically.⁷³^–⁷⁷ The development of deformity is not typically related to a spine fracture but instead seems to primarily be related to a spinal cord injury with lack of trunk motor control and spasticity.⁷³ Spinal deformity is most likely to develop after spinal cord injury in those younger than 18 years and in patients with injuries at or above the T12 level.^73,⁷⁸ During childhood, bracing is frequently recommended to slow progression of the deformity, provide trunk support, and allow growth.⁷⁹

The goals of surgery include optimization of pulmonary function and enhancement of seating in the setting of progressive and severe deformities. Thresholds for surgery may include scoliosis curves of 50 degrees or greater or kyphosis of 70 degrees or greater. Surgery typically includes long segmental instrumentation. Approximately 80% of normal spinal height is achieved by the age of 10 years, and it is therefore preferable to delay surgery until this point if possible. Preoperative MRI should be considered to evaluate for the presence of a spinal cord syrinx, which may require treatment before spinal fusion to prevent further neurological deficit. There are special considerations in this population when contemplating spinal fusion, including loss of mobility, which can compromise the ability to self-catheterize, turn the wheels of a wheelchair, and transfer between bed and chair.

Idiopathic Scoliosis

The cause of the most common pediatric deformity, idiopathic scoliosis, is unknown. It is generally defined as greater than 10 degrees deviation of the spine in the coronal plane without any evident clinical cause. Historically, idiopathic scoliosis has been classified into three groups based on age at diagnosis: infantile (<3 years), juvenile (3 to 9 years), and adolescent (10 years to skeletal maturity) (Figs. 223-7 and 223-8).⁸⁰ Subsequent work has suggested an alternative classification of early-onset (<5 years) and late-onset (5 years to skeletal maturity) idiopathic scoliosis.^81,⁸² The Lenke classification is currently the most commonly applied approach for classification of idiopathic scoliosis.^83,⁸⁴ Briefly, this system is based on both coronal and sagittal radiographs and was primarily developed to help determine 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) based on deviation of the apical lumbar vertebra, and a sagittal plane modifier (−, N, or +).

FIGURE 223-7 Radiographs of a 10-year, 4-month-old girl with early-onset right thoracic idiopathic scoliosis, including preoperative posteroanterior standing (A), supine left-bending (B), and supine right-bending radiographs (C), as well as a lateral (D) radiograph. Also shown are 4-year postoperative posteroanterior (E) and lateral (F) radiographs after instrumented arthrodesis from T5 to L2.

FIGURE 223-8 Radiographs of a 12-year, 2-month-old girl with severe thoracolumbar adolescent idiopathic scoliosis, including preoperative posteroanterior (A) and lateral (B) radiographs, posteroanterior left (C) and right (D) side-bending and traction (E) radiographs, and postoperative posteroanterior (F) and lateral (G) radiographs, 1 year after instrumented arthrodesis from T2 to L4.

Although bracing is the traditional nonsurgical treatment of idiopathic scoliosis, its use is not without controversy because the evidence supporting its benefit is primarily derived from uncontrolled observational studies and patient compliance is variable. The indications for bracing, how it should be used, and the optimal type of brace have not been standardized. For a scoliotic curve with an apex at or below T7, a thoracolumbosacral orthosis may be used (e.g., Charleston, Wilmington, and Boston braces). For curves with an apex above T7, a cervicothoracolumbosacral orthosis may be used (e.g., Milwaukee brace). In general, bracing should be viewed as a treatment that offers stabilization of the deformity and not necessarily correction.

Bracing may be indicated in patients with adolescent idiopathic scoliosis and curves greater than 20 degrees that have been demonstrated to progress more than 5 degrees. Adolescents with significant remaining growth potential who have curves between 25 and 40 degrees may also warrant bracing, even in the absence of documented progression.⁸⁵ Bracing is typically discontinued in adolescents if the curve reaches surgical dimensions (45 to 50 degrees) or once skeletal maturity is attained.

Because bracing in young children may be difficult, observation is generally considered reasonable for patients with juvenile scoliosis until the curve reaches 30 degrees.^86,⁸⁷ Bracing may be used once the curve reaches 30 degrees to allow further growth before considering surgical fusion. Based on a report from Kahanovitz and colleagues, curves of less than 35 degrees with an RVAD of less than 20 degrees are likely to respond to brace therapy, whereas curves greater than 45 degrees with an RVAD of greater than 20 degrees are unlikely to respond to bracing.⁸⁸

Infants with scoliosis curves of less than 25 degrees and an RVAD of less than 20 degrees have a low likelihood of progression, and it is generally acceptable to monitor them with serial radiographs at 4- to 6-month intervals. Annual radiographs may be performed if the curve resolves, but the child must be monitored until skeletal maturity. If the curve does not resolve but instead progresses by more than 10 degrees, the infant should be carefully evaluated ⁸⁹ and consideration given to treatment with casting.

Infants at high risk for curve progression (Cobb’s angle of 25 to 35 degrees and an RVAD of greater than 20 degrees) should undergo serial imaging at 4- to 6-month intervals. Treatment, with bracing or casting, is warranted if the curve progresses by 5 degrees or more. Serial molded body casts are typically used for infants up to 18 months of age. Beyond this age, infants are placed in a brace, often a Milwaukee brace, to be worn at least 23 hours per day. If the curve ultimately corrects, relapse during adolescence is very unlikely.⁹⁰

In children with early-onset scoliosis, bracing and casting are the preferred treatment approaches. If these approaches are contraindicated or fail, surgical treatment may be indicated. Nonfusion instrumentation techniques attempt to control spinal deformity while still allowing spinal growth through serial lengthening procedures until the child reaches an adequate age and skeletal maturity for definitive fusion.⁹¹ There are currently three general approaches for nonfusion instrumentation: (1) a single growing rod with a claw foundation proximally or distally,^92,⁹³ (2) dual growing rods with claw foundations proximally and distally,^93,⁹⁴ and (3) a VEPTR.^35,^36,⁹⁵^–⁹⁹

Surgery for adolescent idiopathic scoliosis is often recommended for growing children once the curves reach 45 degrees. Surgery is also recommended for skeletally mature teenagers who have curves that exceed 50 degrees because curves of this magnitude have a significant risk for progression in adult life.¹⁰⁰^–¹⁰² The goals of surgery include stopping progression of the curve, restoring alignment, balancing the spine in all anatomic planes, and minimizing the number of vertebral levels that are fused. Current posterior instrumentation systems include hooks, wires, or pedicle screws (or any combination of the three), which are typically connected with dual rods. Despite initial concerns of safety, it appears that use of pedicle screws in pediatric patients is safe in experienced hands.¹⁰³^–¹⁰⁷ Regardless of the instrumented system selected, success of the procedure ultimately depends on achieving solid bone fusion.