Introduction

Although spinal deformity can occur across the spectrum of life, scoliosis in the young child presents unique challenges and treatment considerations given the ongoing growth of the spine and lungs. Early-onset scoliosis (EOS) describes the often severe, complex deformities of the spine and thorax, presenting in children younger than 10 years of age. ¹ In fact, by virtue of differences in prevalence, comorbidities, and especially natural history, EOS is distinct from other forms of scoliosis both in terms of treatment strategies and outcomes.

The treatment of EOS remains a challenging and rapidly evolving area of pediatric spine care. A thorough understanding of the natural history of EOS is important in counseling families and treating patients. Treatment options must be continually and critically reassessed as the evidence base grows. This chapter discusses our understanding of the natural history of EOS, etiologies of EOS, and the recently developed Classification of Early-Onset Scoliosis (C-EOS).

Background

Early-onset scoliosis encompasses heterogeneous spinal disorders that are unified only in age and in the presence of spinal deformity. The etiology of scoliosis in the EOS population varies widely and includes congenital scoliosis (i.e., congenital defects in vertebral formation and segmentation), structural scoliosis (i.e., scoliosis that results from fused ribs, chest wall anomalies, and congenital diaphragmatic hernia), scoliosis driven by neuromuscular diseases (e.g., cerebral palsy and muscular dystrophy), scoliosis associated with syndromes (e.g., neurofibromatosis, VACTERL [vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb defects]), and scoliosis that arises in the absence of an identifiable cause (i.e., idiopathic scoliosis). Cognitive, functional, and medical involvement within this population varies from normal to severely impaired. Although the true prevalence of EOS remains poorly defined, EOS accounts for 10% of all pediatric scoliosis cases. ²

Goals of management in EOS include regulating progression of spinal deformity, maximizing thoracic volume, and optimizing function and health-related quality of life while minimizing complications and negative effects of treatment.

Natural History

To understand and appreciate the effect of treatment options in EOS, one must understand the natural history of the disease. The heterogeneous population presents a dilemma when evaluating the effect of spinal deformity or treatment modalities on patients with EOS because existing comorbidities make it difficult to determine what symptoms and changes are attributable to the treatment, the scoliosis, or other medical issues. Comorbidities can be as significant in contributing to patient disability as the spinal deformity, and management by a multidisciplinary team is important for optimal care of patients with early-onset deformity.

Understanding the natural history of EOS is important in defining the incremental value of treatment. The literature on the natural history of untreated EOS is limited. Few patients with EOS remain untreated today, making the natural history of the disease difficult to determine. Studies are few in number, retrospective in nature, and limited by various forms of bias, such as a short follow-up period or a significant number of subjects lost to follow-up. Despite these problems, key studies have increased our understanding of EOS with respect to deformity progression, cardiopulmonary development, and clinical outcomes. This information serves as the foundation for current EOS treatment and ongoing research.

Thoracic Growth and Function

The three-dimensional growth of the thorax is of major importance in the treatment of patients with EOS, given the relationship between structure and function of the spine, thorax, chest wall, and lungs. A working knowledge of normal thoracic and spinal growth patterns affords a better appreciation of the pathological changes induced by early-onset spinal deformity.

Postnatal development of the lungs is characterized by substantial growth during the first 2 years of life. Pulmonary maturation then continues at a slower rate until age 8, at which time alveolar multiplication plateaus. Thoracic distortion secondary to extrinsic spinal or intrinsic chest wall deformity during these early periods can have a substantial deleterious influence on pulmonary development. Pulmo nary deficiency is particularly problematic for patients with neuromuscular scoliosis who may have limited ability to forcibly inhale or exhale secondary to muscular weakness.

An animal model of EOS in the rabbit demonstrates alveolar hypoplasia, decreased lung com pliance, abnormal ventilation, and decreased pulmonary reserve. ³ Similar pathological and histological findings are reported in autopsies of patients with EOS. ⁴ Pulmonary function testing of patients with EOS demonstrates varying degrees of insufficiency secondary to pulmonary hypoplasia, decreased chest wall compliance, and muscular dysfunction. ⁵ Patients with severe EOS can also develop chronic cardiopulmonary issues such as pulmonary hypertension and subsequent cor pulmonale secondary to chronic vascular bed restriction and hypoxemia. ⁵

Deformity Progression

Preventing curve progression remains a primary goal in the treatment of EOS. In the immature patient, the pattern of deformity progression is related primarily to the rate of spinal growth and the underlying etiology of disease. Accurate prediction of patterns of progression is important in guiding the timing of treatment and interventions.

Several authors have studied the growth of the normal spine. The T1–S1 spinal segment grows ~ 2 cm/year for the first 5 years of life followed by 1 cm/year from ages 5 to 10. Growth subsequently increases to ~ 1.8 cm/year until skeletal maturity. ⁶ These two periods of rapid spine growth (from birth to 5 years and from 10 years to maturity) correlate with periods of curve progression in both idiopathic and nonidiopathic scoliosis. ⁷ The following subsections briefly discuss the natural history of deformity progression with respect to each etiology of EOS based on the available literature.

Idiopathic Scoliosis

Idiopathic scoliosis occurs in otherwise healthy individuals without a discernible cause. Patients with idiopathic EOS typically follow a pattern of a progressive worsening or, in some cases, spontaneous resolution of curves. ⁸ Spontaneous resolution of deformity is a unique feature, as most other subtypes of EOS do not typically demonstrate deformity improvement. Reported rates of curve resolution vary widely in the literature between 20% and 80%. ⁸ Progressive curves tend to increase to a severe deformity given the large amount of growth potential within this patient population. Predicting whether idiopathic early-onset deformity will progress can be challenging, and it involves radiographic findings and a review of the pathoanatomy. The apical rib vertebral angle difference (RVAD) was described by Mehta ⁹ as a radiographic tool for identifying progressive curves in idiopathic EOS. The rib vertebral angle is formed between a perpendicular to the upper or lower border of the apical vertebra and a line crossing through the apical rib head and neck. The RVAD is the difference between the rib vertebral angle of the convex side and of the concave side of the curve at the apex ( Fig. 1.1 ).

In a retrospective review of 138 patients with idiopathic EOS diagnosed before age 2, 80% of patients with progressive curves had an RVAD of > 20 degrees at initial presentation. In contrast, 80% of patients with resolving curves had an initial RVAD of < 20 degrees. ⁹ The utility of the RVAD in distinguishing between progressive and resolving curves in idiopathic EOS is supported by other authors, ⁸ though Corona et al ¹⁰ demonstrated variability in measurement of the RVAD.

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