Scoliosis

GENESIS

Scoliosis is the most common deformity of the spine, and it is defined as a lateral curvature of the spine that is 10 degrees or greater on a standing coronal radiographic image.

Congenital scoliosis is caused by a failure of vertebral segmentation, which may lead to progressive spinal deformity with growth. Neuromuscular scoliosis is caused by central nervous system dysfunction (e.g., spastic quadriplegia), peripheral neuromuscular dysfunction (e.g., muscular dystrophy and spinal muscular atrophy), or combined sensory and motor dysfunction (e.g., syringomyelia). Scoliosis commonly occurs in patients with neurofibromatosis or genetic connective tissue diseases (e.g., Marfan syndrome or Ehlers-Danlos syndrome). In most patients with scoliosis, however, the cause is unrecognized and termed idiopathic scoliosis . Idiopathic scoliosis is divided into infantile (in children from birth up to 3 years of age), juvenile (in children 3–10 years of age), adolescent (in children older than 10 years of age), or adult. In adults, scoliosis may be caused by degenerative disk disease. First-degree relatives of a person with scoliosis have a 10% risk of developing scoliosis, suggesting a genetic basis for this condition, but specific genetic determinants remain unclear.

External fetal constraint rarely causes persistent scoliosis but can result in infantile idiopathic scoliosis that responds to physical therapy ( Fig. 20.1 ). Infantile idiopathic scoliosis has been associated with a history of breech presentation, and Lloyd-Roberts and Pilcher studied the natural history of 100 infants with no associated malformations or radiologic defects who presented with a lateral curve of the thoracic spine that did not disappear on suspension (67% male predilection). Convexity to the left was noted in 85% of cases, with similar sex and sidedness predilections as noted for torticollis. The mean angle of curvature was 15 degrees (range 5–40 degrees), and the affected infants were observed for an average of 3 years until complete resolution (92%) or obvious progression (5%), with secondary structural scoliosis (double primary curves) noted in 3%. Because of the high rate of associated torticollis-plagiocephaly deformation sequence (83%), with rib prominence on the convex side (50%) and pelvic tilting that followed the curve of the trunk, these researchers interpreted these defects as being secondary to fetal constraint and used the term molded baby syndrome .

Spontaneous resolution during infancy occurred in most cases of infantile idiopathic scoliosis, but curves with an initial rib-vertebra angle difference greater than 20 degrees that failed to improve in 3 months, or those who developed compensatory curves above and/or below the primary curve, tended to relentlessly progress, compromising cardiorespiratory function. In a study of causative factors of infantile idiopathic scoliosis, Wynne-Davies noted an excess of males, with most curves convex to the left, as well as postnatal development of forehead flattening on the same side as the convexity and accompanied by contralateral occipital flattening. She noted an excess of breech presentation (17.6%), with only 3% of such infants sleeping in the prone position (which she compared with the markedly reduced incidence of infantile idiopathic scoliosis among prone-sleeping North American infants). Among infants with idiopathic scoliosis, 64% were born between July and December, and they developed curves between October and March, suggesting that limitation to free movement resulting from being heavily wrapped during cold weather played a role. Infantile idiopathic scoliosis differs from adolescent-onset idiopathic scoliosis in that it frequently resolves spontaneously, is more common in males, and shows a marked predilection for left thoracic curves, whereas most adolescent-onset cases progress and occur more commonly in females and on the right side. The occurrence of resolving infantile idiopathic scoliosis in Edinburgh, Scotland, was markedly reduced, from 42% of all patients with idiopathic scoliosis in 1968–1971 to 4% in 1980–1982, when infant sleep positioning changed from supine to prone, and centralized heating became more available. Because the current infant sleeping practice has switched back to supine sleep positioning, the incidence of infantile idiopathic scoliosis may increase once again, but this can easily be treated with physical therapy.

Chest and trunk asymmetry is common in otherwise healthy children and adolescents, and few high school students have completely symmetric posture. Among more than 2000 children assessed in a school screening program, 4.1% had positive screening for scoliosis based on rib prominence while standing and bending forward (the Adams forward-bend test), 1.8% had idiopathic scoliosis of greater than 10 degrees, and 0.4% required active treatment. Idiopathic scoliosis is usually not progressive, but the likelihood of progression is higher in girls and in children with a large curvature and remaining growth. Scoliotic deformity that is less than 30 degrees at the end of growth rarely worsens during adulthood, whereas scoliosis of greater than 50 degrees does tend to worsen during adulthood at a rate of 0.75–1.00 degree per year. Therefore a patient with an immature skeleton and scoliosis of greater than 25–30 degrees is at risk for progression. Lung volume doubles between the age of 10 years and skeletal maturity, and growth of the thoracic spine is necessary to achieve adult chest volume. Adolescents with thoracic scoliosis of greater than 50 degrees are at increased risk for shortness of breath later in life. Lung volumes are diminished when idiopathic scoliosis reaches 70 degrees, and symptomatic restrictive pulmonary disease occurs in patients with curves that exceed 100 degrees.

Several risk factors have been set forth for adolescent idiopathic scoliosis, which is of unknown etiology. It is estimated that 20% of scoliosis can be attributed to neuromuscular, syndromic, or congenital disorders, while 80% is idiopathic. Adolescent idiopathic scoliosis is a complex three-dimentional deformity of the spine and trunk, which has a commonly accepted prevalence of 2–3% in the general population, with higher prevalence and severity in girls than boys. The female-to-male ratio increases from 1.4:1.0 for mild curves (10–20 degrees) to 7.2:1.0 for more severe curves (more than 40 degrees). It is thought that tall, slim spines are more likely to bend than shorter, thicker spines, and girls’ spines tend to be more slender with narrower vertebral bodies than boys’. Other factors include joint hypermobility, growth-related factors (height, delayed puberty, and low body mass index), and family history. Using data from the Swedish Twin Registry, the heritability of scoliosis is around 38%.

Progressive scoliosis also has been noted after chest wall resection in children who undergo surgical repair of esophageal atresia, diaphragmatic hernia, or congenital heart defects. The degree of curvature is related to the number of ribs resected, with posterior rib resection leading to scoliosis much more readily than anterior rib resection (which seldom leads to significant scoliosis).

The 22q11.2 deletion syndrome results in a 20–25-fold increased risk for developing scoliosis, with curve progression in 54.2% of cases (mean progression rate of 2.5 degrees/year, similar to idiopathic scoliosis with progression in 49% and 2.2–9.6 degrees/year), and a prevalence of intraspinal anomalies on magnetic resonance imaging of 10.5% in 22q11.2 deletion syndrome (comparable to 11.4% reported for idiopathic scoliosis). Presence of a 22q11.2 deletion, a history of thoracotomy before the age of 12 years, and most severe category of congenital heart disease, but not sex, were significant independent risk factors for scoliosis. The prevalence of scoliosis in those with congenital heart disease, but without a 22q11.2 deletion, was like that of the general population, while among the congenital heart disease population with a 22q11.2 deletion, the prevalence of scoliosis is like that of others with 22q11.2 deletion syndrome, suggesting that this chromosomal deletion is a significant risk factor for both congenital heart disease and scoliosis.

Scoliosis also may result from plural tethering following tumors, irradiation, or empyema. In the past, paralytic scoliosis after poliomyelitis was a cause of scoliosis, and there is progressive neuromuscular scoliosis in spinal muscular atrophy, acute flaccid myelitis with extensive thoracic spinal cord involvement, as well as in Friedrich’s ataxia (90%, with more than 50% requiring surgical intervention). Scoliosis is also common in children with cerebral palsy (41%), with strong associations with poor gross motor function and dystonic movement disorders, particularly in nonambulant children. Boys with Duchenne muscular dystrophy often develop scoliosis that progresses, which can by delayed or prevented by using spinal orthosis, thereby improving sitting position and especially pulmonary function. Spine flexibility is a significant influencing factor for the effectiveness of bracing. There is a period of fully reducible curve in muscular dystrophy patients at the initial onset of scoliosis, but as the spinal curve progresses, flexibility decreases over time, so it is crucial to detect the scoliosis when the curve is fully reducible. Therefore patients should be regularly evaluated radiographically over time.

Patients with anterior chest wall deformities manifest associated scoliosis in more than 20% of cases, and 18% and 14% of patients with pectus excavatum and pectus carinatum, respectively, require therapeutic intervention for scoliosis via bracing or surgery.