6 Surgical Management of Congenital Scoliosis Abstract Congenital scoliosis and kyphosis describe a spectrum of vertebral column defects that result in abnormal growth and spinal deformity. Congenital deformities range from simple, low-risk defects that can be managed nonoperatively to complex, rapidly progressive pathologies that require urgent surgical attention. In order to make proper management decisions, spine surgeons and other providers must have a clear understanding of the specific pathology involved as well as its natural history. Surgical intervention should be considered for high-risk defects, those with demonstrated progression on serial imaging, highly deforming lesions, and those causing neurological or respiratory symptoms. A host of techniques have been employed for the surgical treatment of congenital scoliosis, including in situ fusion, convex growth arrest, hemivertebra excision, posterior spinal fusion with osteotomies and growth preservation techniques. In this chapter, we describe the types of congenital scoliosis and kyphosis, the natural history, patient evaluation and work-up, and provide an expanded discussion on the most common surgical treatment strategies. Keywords: congenital, scoliosis, kyphosis, hemivertebra, hemiepiphysiodesis, convex growth arrest, vertebral column resection, hemivertebrectomy, growing rod, vertical expandable prosthetic titanium rib Clinical Pearls • Convex growth arrest (hemiepiphysiodesis) can be an effective treatment of mild-to-moderate scoliotic lesions in young patients with growth potential; however, they must be followed closely in order to prevent uncontrolled growth. • Hemivertebra excision corrects both the focal deformity and stops asymmetric spinal growth by removing the pathological growth plates, and can be performed safely in young patients before malignant deformity develops. • For rigid and severe deformities, posterior correction with osteotomies and instrumentation may be required. This is often necessary in patients with multiple anomalies and large secondary curves. • Growth preservation techniques, consisting of growing rods and vertical expandable prosthetic titanium rib (VEPTR) technology, are used to slow curve progression while allowing for thoracic expansion as patients mature. The term “congenital scoliosis” refers to spinal deformity that is caused by early developmental spinal anomalies. These congenital anomalies can lead to deformities that impact the coronal plane (scoliosis), sagittal plane (kyphosis), or both (mixed). Curve progression and severity varies significantly with anomaly type, number of vertebrae involved, location within the spine, and skeletal maturity. As such, a firm understanding of the natural history of these lesions guides prognosis and management decisions. Here, we present a review of congenital vertebral anomalies, highlight the progression potential of each type, and discuss current surgical management strategies. Embryological development of the spine occurs in the first 6 weeks of life. Patterning of the spine occurs as somites of the mesoderm segment to form vertebral bodies ventrally and neural elements dorsally. Vertebral defects most often result from either a failure of formation of a vertebral body or a failure of segmentation ( Failure of formation can be incomplete or complete. Incomplete, or partial, failures include wedge vertebrae, which have a complete lateral width with two pedicles present, but a hypoplastic vertebral body height on one side. Complete failures of formation refer to hemivertebrae, where only one of the two sides of the vertebral body forms. Hemivertebrae can be fully segmented, with a present vertebral disc and growth plate above and below the hemivertebra. In contrast, unsegmented hemivertebrae are fused rostrally and caudally to the adjacent vertebrae, and therefore, have limited growth or progression potential on that side of the vertebral body. Partial segmentation too can occur. Incarcerated hemivertebrae are those unsegmented hemivertebrae that sit within a niche of bone in the adjacent vertebrae. These defects rarely cause significant deformity. Failure of segmentation describes the congenital lack of separation between adjacent vertebral bodies. Unlike failures of formation which produce abnormal curvature through asymmetric vertebral height and unequal rates of growth on each side of the vertebral body, failures of segmentation create deformity through a tethering effect that inhibits growth on the concave side of the scoliotic curvature. Unilateral bars are bony columns on one side of the vertebral bodies that can span multiple vertebral levels. They can have very significant effects on curve progression, particularly if they span many spinal levels. Deformity progression becomes most prominent during pediatric growth spurts when spinal growth is most rapid. Bilateral segmentation failure can occur, as well as block vertebrae, which are two fully fused completely formed vertebrae. In these instances, growth inhibition occurs on both sides of the spine, and rarely does deformity develop from such defects. Mixed congenital anomalies can occur as well. For example, a patient may have multiple hemivertebrae, multiple unsegmented bars, or a combination of these defects. Most worrisome are those mixed cases where a unilateral bar is in association with a contralateral hemivertebrae. In this specific scenario, there is an asymmetry from the hemivertebra itself, potential for asymmetric growth on the side of the hemivertebra (the convex side of the curve, particularly if the hemivertebra is fully segmented), and tethering of growth on the concave side of the curve because of the bar. However, in other instances, mixed defects have an opposing effect on each other and can offset one another. When two bilateral hemivertebrae exist within the same region of the spine (typically the thoracic spine), they often balance each other, and are referred to as a hemimetameric shift. Fig. 6.1 Classification of congenital scoliosis. Bony defects are characterized as failures of segmentation and formation. (Reproduced with permission from McMaster M. Congenital scoliosis. In Weinstein S, ed. The Pediatric Spine: Principles and Practice, 2nd ed.; Lippincott Williams and Wilkins Publishers, Inc.) Failures of formation and segmentation can also impact alignment in the sagittal plane. While less common than scoliosis, congenital kyphosis can cause severe deformities, and in extreme circumstances can lead to neurological dysfunction. Large focal deformities can lead to stretching and draping of the cord across sharp angulations of the canal leading to myelopathic symptoms and even spinal cord injury. Kyphotic failures of vertebral body formation are similar to those in scoliotic disease ( Fig. 6.2 Classification of congenital kyphosis. Bony defects are similar to those seen for bony scoliotic defects, but create deformity in the sagittal plane rather than the coronal plane. These can occur in conjunction with scoliotic defects and result in kyphoscoliosis. (Reproduced with permission from aster M, Singh H. Natural history of congenital kyphosis and kyphoscoliosis. A study of one hundred and twelve patients. McMJournal of Bone 81 (10):1367-1383. Wolters Kluwer Health, Inc.) Failures of segmentation of the spine in the sagittal plane are similar to those bony bridging bars that occur in scoliotic disease. These can occur in the midline and produce a purely kyphotic deformity, or slightly laterally, and produce kyphoscoliosis. Such bars typically result in broad sweeping curves that worsen with growth. As with congenital scoliotic defects, mixed defects can also occur, which can either have additive effects or offset one another. Congenital kyphotic deformities place the spinal cord at greatest risk due to focal draping and/or ventral bony compression due to the anomaly. Patients with severe focal kyphotic angulations should especially be evaluated for the presence of neurological deficits, including evidence of weakness or signs or symptoms of hyperreflexia/spasticity, both based on their history and on clinical examination. Dedicated magnetic resonance imaging (MRI) is a necessary adjunct in these cases. Our knowledge of the natural history of these lesions is primarily derived from exemplary studies by both Winter and McMaster.1,2,3 Despite the rarity of these lesions, they were able to assemble a large case series, develop classification schemes, and document curve progression of the various types over time. These studies have provided the foundation for current treatment recommendations. Several generalizable findings can be concluded from their work. First, curve progression occurs most rapidly during the first 5 years of life and during the pubertal growth spurt. Patients with high-risk deformities, such as a hemivertebra with a contralateral bar, may require surgical intervention at a very young age to prevent progression and subsequent morbidity/deformity. For low-risk deformities, it is important that patients with congenital deformities be monitored until their growth cessation, as even stable curves can rapidly progress during puberty. Secondly, deformities of various regions of the spine need to be evaluated differently. Deformity in some parts of the spine can yield more visible deformity and present sooner. For example, high thoracic curves often are poorly tolerated due to shoulder tilt. Listing of the head and neck occurs due to inability of secondary cervical curves to correct over this relatively short spinal region. Similarly, lumbosacral lesions can create significant pelvic obliquity, which in many instances affects not only posture, but gait. There are also regional differences noted in rates of progression. For example, junctional regions of the spine, particularly the thoracolumbar and lumbosacral regions, demonstrate high rates of progression. Lastly, mixed deformities can be very difficult to distinguish and prognosticate. As mentioned above, their laterality with respect to one another, number, distance of separation, and location within the spine can all affect their expected rate of progression. Large heterogeneity of mixed lesions makes predictability very challenging. Since they can progress more rapidly than solitary lesions, close radiographic and clinic monitoring is recommended. Fig. 6.3 Annual rates of deformity progression determined by defect type and location from McMaster’s original series of 251 patients. Anticipation of angular progression guides management decisions. (Reproduced with permission from McMaster M, Ohtsuka K. The natural history of congenital scoliosis. A study of two hundred and fifty-one patients. Journal of Bone 64(8):1128-1147. Wolters Kluwer Health, Inc.) Embryonic malformations that result in congenital vertebral defects often are associated with insults to development of other organ systems that form at the same time. Therefore, it is important to examine all patients with a new diagnosis of congenital scoliosis for coexisting defects. These include intraspinal, musculoskeletal, genitourinary, cardiac, and gastrointestinal anomalies. The likelihood of having an associated anomaly is increased with mixed defects. Complete neurological physical examination helps to evaluate for signs and symptoms of intraspinal disease. Neurological symptoms, including myelopathy, weakness, numbness, spasticity/contracture, or bowel or bladder dysfunction, warrant immediate work-up for underlying pathology. The most commonly associated intraspinal disorders include tethered spinal cord, diastematomyelia, syringomyelia, the Chiari malformations, Dandy–Walker malformations, or intraspinal lipomas. MRI of the spine can aid in the diagnosis, and should be performed in patients with congenital scoliosis, particularly if surgical intervention is being considered. Many of these disorders may augment the rate of deformity progression, and as such, treatment of intraspinal anomalies should precede the correction of scoliosis. Deformity correction in the presence of an untreated tethered or split cord or herniated cerebellar tonsils may cause severe neurological injury. Skeletal anomalies can occur anywhere throughout the body, including craniofacial defects, limb or pelvic abnormalities, and rib defects. Defects of the thoracic wall, including congenital rib fusions or missing ribs are common, especially with segmentation defects, owing to the closely tied nature of vertebral and rib development. Severe rib defects can result in stunted thoracic growth, and in some cases with long segment defects of the thoracic spine, restrictive pulmonary capacity, or thoracic insufficiency syndrome. Radiographs of the spine are essential in the evaluation of congenital defects of the spine. Standing anterior–posterior and lateral X-rays allow for visualization of vertebrae, as well as measurement of relative anatomical landmarks, Cobb’s angles to evaluate curvatures, and other relative asymmetries, such as pelvic obliquity and shoulder tilt. Skeletal maturity can also be determined using the Risser Scale, which may help in prognosticating curve progression during adolescent growth spurts. Serial measurements of Cobb’s angles over time may be used to determine relative rates of change over time, and help determine if the rate of progression warrants surgical treatment or continued observation. Lateral bending radiographs may also be helpful during surgical planning in determining the flexibility of curves and identifying secondary curves that may not need to be included in posterior instrumentation. As mentioned above, MRI plays a useful role in identifying intraspinal anomalies. MRI also can be helpful in evaluating disc spaces to determine if hemivertebrae are segmented and contain growth potential. In cases of severe focal kyphotic deformities, MRI is critical for evaluation of the spinal canal and spinal cord compression. Similarly, computed tomography (CT) imaging with three-dimensional reconstruction can be illustrative for the surgeon evaluating the vertebral and rib anomalies. This is particularly true when severe deformities create radiographic crowding on plain radiographs that limits their interpretation. As with MRI, vertebral body defects can be more precisely defined on CT reconstructions. As discussed above, the expected trajectory of the various congenital vertebral curves varies widely. A thorough understanding of the specific anomalies and their progression risk guides treatment decision making. Benign lesions such as block vertebrae and fully incarcerated hemivertebrae rarely progress to the point of warranting surgical correction. Conversely, lesions such as a unilateral bar with a contralateral hemivertebra may warrant early, and sometime prophylactic, surgical treatment before the deformity puts the patient at serious risk. Therefore, nonoperative management with close monitoring requires tailoring of the level of observation according to the risk of the lesion. Continuous documentation of neurological function and pulmonary function in cases of severe thoracic lesions is vital. Serial radiographs every 6 to 12 months until the end of skeletal maturity are recommended to monitor deformity progression. More frequent imaging may be performed during phases of rapid growth (i.e., during the first 5 years of life and during the adolescent growth spurt). Ultimate deformity magnitude cannot be determined until after skeletal maturity. Unlike some other types of scoliosis, bracing alone is rarely beneficial for treatment of congenital scoliosis. Curves associated with congenital vertebral defects are rigid, and consequently are rarely impacted by external forces. Moreover, in severe cases of thoracic defects where thoracic insufficiency is a concern, bracing may have deleterious effects. There is some evidence that bracing may help control severe secondary curves that can develop above or below a congenital primary curve, though bracing is rarely performed for this purpose. Likewise, bracing may be considered for postoperative stabilization after surgical fusion procedures. Decision making on the proper treatment of congenital scoliosis requires a clear understanding of the natural history of the various types of congenital defects, as discussed above. Surgical correction is necessary in patients with either severe deformity or with anomalies that are at high risk for rapid progression. In general, the goal is to surgically treat high-risk lesions before they become problematic, without treating lower-risk patients unnecessarily. The most severe curves often require aggressive surgical techniques such as three column osteotomies and thus carry a high surgical complication risk. Early treatment can minimize surgical risk and also to help to prevent secondary issues such as thoracic insufficiency and neurological deficits. Studies have demonstrated that early focal surgical correction can be performed safely and without adverse effects on patient’s vertebral or thoracic growth. Surgery is also considered in patients who fail nonoperative management, for example, curves that progress beyond 60 degrees, or in cases where the curve is less than 60 degrees, but the yearly rate of progression is high and suggests that further observation is futile. Likewise, deformity of the upper thoracic and lumbosacral regions can result in visible deformity of shoulder and pelvic tilt, respectively. The disfiguring nature of these curves can be particularly distressing to patients, even with smaller curves, and therefore, surgical correction can be considered. All patients should be treated by surgeons with experience in treating spine deformity, and an understanding of the periprocedural risks inherent to scoliosis surgery. Specifically, attention must be paid to several key areas through the case. The first is minimizing blood loss, particularly with instrumented fusions, vertebral resections, and osteotomies, as this may result in considerable intraoperative hemorrhage. Appropriate monitoring of serial blood gases, blood hemoglobin concentrations, and replenishing of platelets and clotting factors helps to reduce the risks associated with periprocedural anemia. In general, a preoperative discussion and plan with the anesthesia and operating room team should be performed to help coordinate these efforts prior to the commencement of the case. Throughout the case, hypotension should be avoided to ensure adequate spinal cord perfusion. Mitigating risk of neural injury during spinal manipulation is another important consideration. Intraoperative multimodal neuromonitoring, including somatosensory evoked potentials and motor evoked potentials, should be utilized. Neuromonitoring is used to detect neurological dysfunction during surgery and allows for early intervention (e.g., reversal of surgical maneuvers, elevation of systemic blood pressure to augment spinal cord perfusion, etc.) to protect against neurological injury. This is especially important in cases of severe kyphoscoliotic disease which carry a high risk of intraoperative neurological injury. In situ fusion is a simple method of providing stabilization across a defect to prevent focal curve progression. This approach remains limited in its scope, as it does not provide any correction, and therefore, can only be applied to patients who have small curves (usually < 30 degrees) that are identified early in life, but are expected to progress significantly enough later in life that they warrant early prophylactic surgery. Given these limitations, this technique is not commonly employed. If the decision to treat with in situ fusion is made, short-segment posterior instrumented fusion across the defect can be performed. Anterior fusion should also be considered in most cases to prevent a crankshaft phenomenon. This occurs when a lordotic anomaly develops in response to preserved anterior growth potential in the presence of a posteriorly fixated segment. In cases of mild, focal kyphotic disease with posterior fusion alone, this anterior growth can actually be used strategically to yield small amounts of correction with growth. Likewise, in focal lordosis, an anterior alone treatment could be performed reciprocally with the same goal. Patients should be followed very closely after this procedure to monitor for fusion and disease progression. Early continued progression may indicate pseudoarthrosis and surgical exploration and revision may be considered. Delayed curve progression may warrant reoperation with long-segment posterior fusion (discussed below) and curve correction. Congenital scoliotic deformity is primarily caused by longitudinal growth imbalance; growth of the convexity outpaces the concavity and results in abnormal curvature. Epiphysiodesis is the process of removing the growth potential of bones to prevent progression of asymmetry. For congenital spinal disorders, this strategy is used to arrest growth on the convex side of the curve to prevent curve progression and allow for reversal of the deformity as growth continues on the concave side. This treatment option is best considered in young patients where there is the greatest potential for spontaneous correction of the scoliosis during development ( While the indications for convex growth arrest have been contested in the literature, the technique does seem to be well suited for specific types of patients. In general, the indications include patient age less than 5 years, a pure scoliotic curve, short-segment deformities with less than five segments involved, documented curve progression or high-risk defects with Cobb’s angle less than 70 degrees, absence of cervical spine deformity, patients with anomalies due to failure of formation failure over segmentation failure, and absence of neurological deficits or other associated intraspinal/dysraphism abnormalities. Nevertheless, the application of this technique has been tested outside of these boundaries, largely with good outcomes, and these remain as loose guidelines.4 The presence of a contralateral bar hindering concave growth limits the corrective potential of the procedure. When hemiepiphysiodesis is indicated, it is recommended to be carried out from both anterior and posterior approaches. Most commonly, the anterior fusion targets the index levels of the congenital malformation, and the posterior fusion extends one level above and below the defect. Anteriorly, the convex lateral halves of the disc, growth plate, and bony endplate are resected. Posteriorly, facet joints are removed on the convex side with decortication of the laminae and transverse processes to promote fusion. Supplemental unilateral instrumentation may be considered and autogenous bone graft can be used anteriorly and posteriorly to augment the fusion. Patients are typically treated with a postoperative body cast for four to sixth until radiographic fusion has been confirmed. Importantly, patients should continue to be observed after treatment as a minority of patients will continue to display curve progression postoperatively. Hemivertebrae create both a direct angulation of the spine at the site of the deformity, and also lead to curve progression due to growth asymmetry, particularly if they are segmented. Resection of the anomalous hemivertebral body allows for immediate correction of the primary angulation, and also can help restrict the accompanying growth potential. As such, use of this technique is applied whenever it can be safely performed. Dramatic improvements in the scoliosis or kyphosis can be seen, and it is particularly effective for lumbosacral defects.5 Anterior–posterior combined and posterior-only approaches can be used to perform this procedure. Closure of the wedge after excision initially was accomplished with braces and casts, then subsequently by hooks and compression rods with advances in fusion instrumentation. Many surgeons now advocate for a posterior single-stage hemivertebra excision with posterior transpedicular fixation to achieve fusion. However, some surgeons still prefer an anterior and posterior two-stage strategy as they feel that this is safer and involves lower risk of neurological complication. The inclusion of an anterior approach may also be considered if there is a kyphotic defect requiring an anterior cage to maintain anterior column support or to be used as a fulcrum to restore lordosis. Compared to other surgical treatments, hemivertebra excision has several advantages. Firstly, it can be performed in very young patients, and has been advocated for use in children ages 1 to 6 if the defect is identified early in order to prevent disease progression. This has been shown to be very safe and efficacious, and does not limit vertical growth as patients age.6 Additionally, the number of instrumented levels required is only as few as is necessary to allow for fusion across the compressed hemivertebra excision site. In cases of a single hemivertebra without associated bars, rib synostosis or other major structural changes, this requires only the two adjacent vertebrae. If high amounts of compressive force are required to correct the deformity, particularly in instances of severe kyphoscoliosis, an additional one or two segments allow for shared loading and reduce the risk of hardware failure or pedicle fracture. In the posterior-only approach, pedicle screws are first placed into the adjacent vertebra to be included in the fixation. Once this is complete, the posterior elements are removed, including the lamina, facet joints, transverse process, and the posterior part of the pedicle. In the thoracic spine, an extrapleural approach is required, and therefore, the rib head on the convex side needs to be resected to gain exposure to the anterior aspect of the hemivertebra. A retroperitoneal exposure is required for lumbar hemivertebra. While protecting anterior vascular structures and associated neural structures, the defect and adjacent intervertebral disc materials need to be resected, and the adjacent growth plates rasped to enhance fusion. Screw-rod compression across the defect must be performed with direct visualization of the nerves and spinal cord to prevent neurological injury (
6.1 Introduction
6.2 Congenital Vertebral Anomalies
6.2.1 Congenital Scoliosis
Fig. 6.1). Additionally, disorders during chondrification can result in fused vertebral segments with absent growth potential at the cartilaginous growth plates.
6.2.2 Congenital Kyphosis
Fig. 6.2). Some of these defects may occur as a result of failed vascularization of the centrum during the chrondrification stage of development. A posterior hemivertebra, also referred to as a posterior hemicentrum, can exist with anterior hypoplasia of the body. Lateral hemicentrum and posterior quadrant centrum defects can also occur with aplasia of the anterolateral body. Unlike a posterior hemicentrum, which produces a pure kyphotic deformity, these two defects can also create a coronal asymmetry with consequent combined kyphoscoliotic deformity. Complete aplasia of the centrum can also occur with existing pedicles attached to no vertebral body. As expected, these result in severe degrees of kyphotic angulation and can lead to neurological dysfunction; complete aplasia of the centrum is the most likely type to be complicated by spinal cord injury. Also, a unique sagittal cleft vertebra can occur, referred to as a butterfly vertebra, and is the result of an anteromedial and central formation failure, leaving two posterolateral fragments of bone attached to the posterior neural arch.
6.3 Natural History
Fig. 6.3 summarizes the expected annual rates of progression for congenital anomalies and is organized by anomaly type and specific location within the spine. The table is somewhat limited in that it does not account for patient age and does not include all mixed defects. Some defects follow this patterning fairly well, including unilateral bars. However, bars that span eight spinal levels may behave very differently than those that only involve two levels. Moreover, high variability can occur even among patients with a single isolated hemivertebra. Therefore, while this may serve as a guide for prognostication, it remains very difficult to predict behavior of congenital anomalies with any real precision. Close clinical and radiographic monitoring is needed to tailor the appropriate treatment to any individual patient.
6.4 Preoperative Assessment
6.4.1 Evaluation of Associated Anomalies
6.4.2 Imaging Evaluation
6.5 Nonoperative Treatment
6.6 Operative Intervention
6.6.1 Indications for Surgical Intervention
6.6.2 Intraoperative Considerations
6.6.3 In situ Fusion
6.6.4 Convex Growth Arrest (Hemiepiphysiodesis)
Fig. 6.4).
6.6.5 Hemivertebra Excision
Fig. 6.5).
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