Current Concepts in the Management of Early-onset Idiopathic Scoliosis

Ujjwal K Debnath

Disclosures

Pediatr Health. 2010;4(3):343-354. 

In This Article

Growth & Development of Spine

A relationship between growth of the spine and progression of spinal deformity exists as observed by previous authors.[11,12] Therefore, it is imperative that this relationship is explored further through research since the current available information is insufficient and ill defined.[13] The two main components of the scoliosis are spinal deformity and respiratory compromise. Therefore, the normal development of these two effects must be understood.

Spine

After birth, the primary ossification centers in each vertebral body expands to demarcate the parallel growth plates. The physeal growth (both superior and inferior) leads to the longitudinal growth under physiological stress.[14] Each vertebra also expands circumferentially by interstitial growth in the physes. The cortex of the vertebral column enlarges at the same time to give a structural support. The physes ceases to grow once the physiologic stimulus of growth has ceased.[14] The ring apophysis fuses with the metaphysis, which is under the influence of sex hormones.

How and when does the normal spinal growth is disturbed in idiopathic scoliosis is a matter of speculation. Theories include neuromuscular imbalance, subtle physeal abnormalities or spinal cord dysfunction. Spinal growth is maximum by the age of 5 years and then the growth slows down. There is another peak growth after the age of 10 years but the growth velocity is slower than the first 5 years. The longitudinal growth of the thoracic and lumbar vertebrae is 0.8 and 1.1 mm per year, respectively. For all practical purposes, each vertebra (two vertebral ring apophyses per vertebra) contributes 1 mm per year to vertebral column height.[15] The spine gains approximately 10 cm in length between birth and 5 years of age, accounting for the often rapid progression of EOS curves during this time.[4] Most of the pubertal growth spurt acceleration is from the trunk and spine, which gain approximately 10 cm.[4]

Progression of deformity is slow in the cartilaginous phase, but becomes more evident with increasing ossification.[16] The growing vertebra responds to axial loading in accordance with the Hueter–Volkmann laws (i.e., growth is inversely proportional to the mechanical stress). In idiopathic scoliosis, the vertebrae that are parallel at birth in the frontal plane become wedged in three dimensions, causing vertebral torsion.

Thorax

During the first year of life there is increase in the alveolar growth and number in the terminal respiratory unit. Until the age of 8 years, there is maximum increase in the number of the alveoli.[17] The growth of spine and chest corresponds to the pulmonary growth. The thoracic spinal growth is completed at skeletal maturity. Thoracic volume increases to 50% adulthood by the age of 10 years. The adult thoracic volume is reached by the age of 15 years.[4] The long-term pulmonary sequelae are observed in EOS.[6] This was subsequently confirmed from Sweden that increased risk of deaths due to respiratory failure was seen in EOS who had non-operative treatment.[18]

Etiology

The etiology of EOS is probably multifactorial. The two suggested theories described in the past were based on epidemiological studies. One proposes the intrauterine molding theory that is associated with plagiocephaly and limited hip abduction.[19] The side of the plagiocephaly was related to the convex side of the scoliosis, the side of the hip dysplasia, bat ear and the sternomastoid tumor.[20] This theory has been refuted since scoliosis is not present at birth. The other theory, described by Mau, is of postnatal pressure by constant oblique supine position in the European babies compared with the prone positioning of the North American babies. They suggested that this positioning was responsible for the increased incidence of EOS in the Europeans.[21] These studies are speculative and have no relationship to observations made on real children. In fact, EOS is almost unheard of before the age of 3 months, by which time a normal baby has achieved enough independent mobility to position itself, and no longer lies as it was placed. At present, the American Academy of Pediatrics follows a protocol for infants to lie supine to reduce the incidence of sudden infant death syndrome.[22] A current estimate of the prevalence of EOS may be required in the USA in order to question the proposed theory from the past.

Early-onset scoliosis is not associated with any obvious vertebral anomalies. The genetic basis of the disease is similar to the adolescent idiopathic scoliosis. Several studies have demonstrated the familial nature of the disease.[23,24] Wynne-Davies suggested multiple gene inheritance pattern.[23] Cowell et al. selected 17 families (192 individuals) for physical and radiographic examination and reported a pattern consistent with an X-linked inheritance.[25] This evidence was supported by Justice et al. in 2003.[26] The modern technology of genome-wide scanning and statistical linkage analyses of families with scoliosis has resulted in potential linkage to regions on the autosomes.[27,28] Candidate regions on chromosomes 6, 9, 16 and 17 were observed to have strong evidence for linkage.[29] Other authors have identified the genetic locus on 19p13 chromosome to have a potential role in the etiology of this disease.[30,31] Recent genetics research has discovered DNA markers that are associated with progression to a severe curve in idiopathic scoliosis, providing new information that can lead to more effective care with lower cost.[32]

There is no strong scientific evidence implicating any particular biomechanical factor in the etiology of EOS or adolescent scoliosis. A possible role of growth hormones or growth-modulating chemical factors (e.g., clamodulin and melatonin) cannot be ruled out. The reported abnormalities of connective tissue, skeletal muscle, platelets, spinal column and rib cage are all thought to be secondary to the deformity itself. Abnormal MRI findings, microlesions in the brains of experimental animals and the most consistent clinical neurological studies point to the pontine and hindbrain regions as the likely sites of primary pathology that could lead to idiopathic scoliosis.[33]

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