Scoliosis Disease
Introduction and Definitions
Scoliosis is a lateral curvature of the spine in the coronal plane combined with rotation in the axial plane, producing the characteristic three-dimensional deformity of the spine that distinguishes true structural scoliosis from postural lateral lean or pain-related list. The condition encompasses a heterogeneous group of disorders with different etiologies, natural histories, and treatments. The principal categories are: idiopathic scoliosis, divided by age of onset into infantile (0-3 years), juvenile (4-9 years), and adolescent (10-18 years) forms; congenital scoliosis (discussed in detail in the previous chapter); neuromuscular scoliosis arising from underlying neurological or muscular disease; and the syndromic scolioses associated with connective tissue disorders, skeletal dysplasias, and other systemic conditions. Adult scoliosis is the persistence or new development of curve in skeletal maturity. This chapter, synthesizing content from Rothman-Simeone The Spine, Tachdjian’s Pediatric Orthopaedics, Apley & Solomon’s, and Miller’s Review, focuses primarily on idiopathic scoliosis (the commonest form) and on neuromuscular and adult scoliosis, with cross-reference to the preceding chapter for congenital disease.
Adolescent Idiopathic Scoliosis (AIS)
Epidemiology Adolescent idiopathic scoliosis is by far the commonest form of scoliosis, affecting approximately 2-3% of the adolescent population to some degree (curves >10°), with curves significant enough to require treatment (>30°) occurring in approximately 0.3-0.5% of adolescents. The condition predominantly affects girls, with a female-to-male ratio of approximately 8:1 for curves requiring treatment. The right thoracic curve is the typical pattern. The peak age of presentation is 11-14 years in girls and 12-15 years in boys, corresponding to the adolescent growth spurt during which curve progression is most rapid. Etiology and Pathogenesis The etiology of idiopathic scoliosis is unknown, and the term “idiopathic” itself reflects this gap in understanding. Multiple theories have been proposed: genetic susceptibility (a strong genetic component is established by family and twin studies, with several genetic loci identified though no single major gene); hormonal factors (the female predominance and the timing of peak progression at puberty implicate hormonal regulation, with melatonin, leptin, and estrogen all studied); biomechanical factors (asymmetric loading of the immature spine); neurological factors (subclinical brainstem abnormalities have been detected in some series); and connective-tissue factors. The current consensus is that AIS is a multifactorial condition with multiple contributing factors operating in genetically susceptible individuals.
Clinical Features Most adolescent idiopathic scoliosis is detected by school screening, by parents noticing asymmetry, or during routine medical examinations. Symptoms are typically minimal in adolescence, although mild back pain is reported in 20-30% of patients (a rate similar to that of normal adolescents) and severe back pain should raise suspicion of an alternative diagnosis. The classical clinical features are: asymmetric shoulder height with the shoulder elevated on the convex side of the thoracic curve; asymmetric scapular prominence with the convex-side scapula more prominent; waist asymmetry with the concave-side waist appearing more concave; and the most reliable sign — the rib hump (or lumbar hump) seen on Adam’s forward bend test, in which the patient bends forward at the hips and the examiner observes the back tangentially for asymmetric prominence indicating rotational deformity. The Adam’s forward bend test is the gold standard physical examination for scoliosis screening. The patient bends forward with feet together, knees straight, arms hanging freely. The examiner views from behind and observes for asymmetric prominence of the ribs (thoracic curve) or paraspinal muscles (lumbar curve). The scoliometer — a simple inclinometer placed over the apex of the rib hump — quantifies the rotational deformity; a measurement of 7° or greater warrants further radiographic evaluation. Imaging The standard radiographic assessment of scoliosis is a long-cassette posterior-anterior (PA) standing whole-spine radiograph and a lateral standing whole-spine radiograph. The PA rather than AP projection is used to reduce the radiation dose to the breast tissue of the predominantly female adolescent population. The Cobb angle is the standard measurement: lines are drawn along the superior endplate of the most-tilted upper end vertebra and the inferior endplate of the most-tilted lower end vertebra of the curve, perpendiculars are erected to these lines, and the angle between the perpendiculars is the Cobb angle. The end vertebrae are those most tilted into the concavity of the curve. Reliable measurement requires consistent identification of the same end vertebrae. The Risser sign, evaluated from the iliac crest apophysis, is the principal radiographic indicator of skeletal maturity. The iliac apophysis ossifies from lateral to medial, with Risser 0 (no apophysis visible), Risser 1 (25% of the crest), Risser 2 (50%), Risser 3 (75%), Risser 4 (complete excursion), and Risser 5 (fusion of the apophysis to the iliac crest). Risser 0-2 indicates substantial remaining growth potential and high progression risk; Risser 4-5 indicates near-complete skeletal maturity. The Sanders skeletal maturity classification, based on hand and wrist radiographs, provides finer resolution of skeletal maturity, particularly useful in distinguishing the pre-peak from the post-peak growth velocity periods. MRI is not required for typical adolescent idiopathic scoliosis but should be obtained for atypical features that suggest an underlying condition: left thoracic curves (idiopathic scoliosis is typically right thoracic, and left thoracic curves carry an elevated risk of intraspinal pathology), atypical neurological findings, painful curves, juvenile-onset curves, rapidly progressing curves, and curves in boys (where intraspinal pathology is more
common than in the typical female adolescent population). Common findings on MRI include syringomyelia, tethered cord, Chiari malformation, and intraspinal tumor. Curve Patterns and Lenke Classification The Lenke classification (2001) is the standard modern system for adolescent idiopathic scoliosis, replacing the older King-Moe classification of thoracic curves. The Lenke system classifies curves by three components: (1) the curve type (Types 1-6, based on which curves are structural — major thoracic with non-structural lumbar; double thoracic; double major; triple major; thoracolumbar/lumbar; thoracolumbar/lumbar with major thoracic); (2) a lumbar modifier (A, B, or C based on the position of the lumbar curve relative to the central sacral vertical line); and (3) a thoracic sagittal modifier (-, N, or + based on the T5-T12 sagittal profile). The classification has 42 possible combinations and is highly reliable; it guides surgical planning by indicating which curves require fusion and which can be left as compensatory non-structural curves. Natural History The natural history of adolescent idiopathic scoliosis is one of variable progression depending on curve magnitude, skeletal maturity, and curve pattern. The classic data from Lonstein and Carlson (1984) established the progression risk of curves: curves under 20° in patients with Risser 0-1 progress in 22% of cases; curves 20-29° in the same group progress in 68%; curves over 30° at Risser 0-1 progress in over 90% of cases. Once skeletal maturity is reached (Risser 4-5), the risk of further significant progression in adolescence falls to less than 5%. The natural history into adulthood is more complex. Curves over 50° at maturity tend to progress slowly over decades, with rates of 0.5-1° per year on average; curves under 30° at maturity typically remain stable. Thoracic curves over 100° produce pulmonary restriction with reduced vital capacity; curves over 50° in the thoracolumbar region may produce significant pain and disability in middle age. Cosmetic concern remains an important consideration in long-term outcome.
Treatment The treatment of adolescent idiopathic scoliosis follows a sliding scale based on curve magnitude, skeletal maturity, and progression risk. Observation: Curves under 20-25° in skeletally immature patients and curves under 50° at skeletal maturity are observed with serial clinical and radiographic assessment at 4-12 month intervals depending on growth status. Bracing: Curves 25-45° in skeletally immature patients (Risser 0-2) are candidates for bracing. The Boston brace (a thoracolumbosacral orthosis, TLSO) is the most commonly used in North America; the Milwaukee brace (a cervicothoracolumbosacral orthosis, CTLSO) is used for high thoracic curves (apex above T7). The Charleston bending brace is a nighttime-only brace that applies overcorrection of the lumbar curve. The BrAIST trial (2013) provided the strongest evidence for bracing efficacy in idiopathic scoliosis,
demonstrating that bracing significantly reduced the rate of progression to the surgical threshold (50°) compared with observation, with a clear dose-response relationship: more hours of brace wear produced better outcomes, with full-time wear (>18 hours daily) producing the best results. Bracing does not reliably correct existing curves but rather slows or prevents further progression. Surgery: Curves >45-50° in skeletally immature patients and curves >50° at skeletal maturity are typical surgical indications. The standard surgical treatment is posterior spinal fusion with instrumentation. Modern segmental pedicle screw instrumentation has replaced the older Harrington rods of the 1960s-1980s, which provided distraction-only correction and had high rates of late complications. The Cotrel-Dubousset system introduced segmental hook instrumentation in the 1980s and pedicle screw constructs have progressively dominated practice in the 1990s and 2000s. Modern correction techniques combine direct vertebral derotation, segmental compression and distraction, and translational maneuvers to achieve three-dimensional correction. The selection of fusion levels follows several principles: the fusion should include all structural curves; the fusion should end at a stable vertebra (the vertebra most closely bisected by the central sacral vertical line); the fusion should end at a neutral vertebra (one without rotational asymmetry); and the fusion should end one or two levels above and below the structural curve to allow compensation. The Lenke classification guides these decisions for each curve type. Anterior surgical approaches (anterior thoracoscopic or open thoracotomy with anterior instrumentation) were popular in the 1990s and early 2000s for selective fusion of thoracolumbar and lumbar curves, with the theoretical advantage of saving fusion levels; current practice has largely returned to posterior-only surgery with pedicle screw instrumentation, which can achieve comparable correction with greater versatility. Specific complications of scoliosis surgery include: blood loss (substantial in major spinal surgery, mitigated by intraoperative cell salvage, antifibrinolytics, and meticulous technique); neurological injury (rare but devastating, with risk monitored by intraoperative neurophysiological monitoring including somatosensory and motor evoked potentials, with the Stagnara wake-up test as historical confirmation); pseudarthrosis and instrumentation failure; infection; adjacent-segment problems including junctional kyphosis and adjacent-segment disease; and crankshaft phenomenon (continued growth of the anterior vertebrae after posterior fusion in skeletally immature patients, producing late rotational and lateral deformity, mitigated by either delaying posterior fusion until later in growth or by combining anterior and posterior fusion).
Infantile and Juvenile Idiopathic Scoliosis
Infantile idiopathic scoliosis (onset 0-3 years) is the rarest form of idiopathic scoliosis in North America but is more common in Europe. Most cases resolve spontaneously, but a proportion progress relentlessly. The rib-vertebral angle difference (RVAD) of Mehta is the principal predictor of progression: an RVAD >20° on the convex side compared with the concave side at presentation predicts progressive disease. Treatment of progressive
infantile scoliosis was historically problematic because the small spine of an infant cannot accommodate definitive fusion without producing severe truncal disproportion at maturity. The Mehta serial casting technique — sequential application of derotational casts that mold the deformity over months — has produced excellent results in selected cases. Growth-friendly surgical techniques (vertical expandable prosthetic titanium rib — VEPTR, magnetic growing rods — MAGEC, traditional growing rods) are used when casting fails or when severe disease demands earlier intervention; the techniques allow continued spinal growth while controlling the deformity until later definitive fusion. Juvenile idiopathic scoliosis (onset 4-9 years) is intermediate in features between infantile and adolescent forms. The progression risk is high, and bracing and growing-rod techniques are commonly required.
Neuromuscular Scoliosis
Etiologies Neuromuscular scoliosis arises from underlying neurological or muscular conditions that compromise the muscular control of the spine. The principal etiologies include: cerebral palsy (the commonest cause, with severity of scoliosis correlating with GMFCS level — GMFCS V patients have prevalence approaching 70%); spinal muscular atrophy; Duchenne and Becker muscular dystrophy; myelomeningocele; Friedreich ataxia; Charcot-Marie- Tooth disease; poliomyelitis (now historical in most regions); traumatic spinal cord injury; and arthrogryposis. Clinical Features Neuromuscular scoliosis differs from idiopathic scoliosis in several important respects: (1) the curve patterns are typically long C-shaped curves spanning the entire spine, with pelvic obliquity that produces functional sitting difficulties; (2) progression continues into and after skeletal maturity, in contrast to idiopathic scoliosis; (3) pulmonary compromise from chest-wall deformity is more frequent and more severe; (4) bony quality is often poor (steroid-related osteoporosis in DMD, disuse osteoporosis in non-ambulatory patients); (5) the underlying disease produces additional medical complexity that affects perioperative management. Treatment Bracing has a limited role in neuromuscular scoliosis: it does not prevent progression of the underlying paralytic curve, but it can provide truncal support that improves sitting balance in non-ambulatory patients. The decision for surgery is based not on curve magnitude alone but on functional considerations including sitting balance, pulmonary function, pain, and the trajectory of the underlying disease. Surgical management typically requires longer fusion than for idiopathic scoliosis, often extending to the pelvis (the iliac screw or S2-alar-iliac screw fixation in older patients, Luque-Galveston technique with unit rods historically). The principles of segmental instrumentation, attention to sagittal balance, and pelvic obliquity correction are critical.
The complication rates are substantially higher than for idiopathic scoliosis: infection (10- 20%), pulmonary complications, gastrointestinal complications, and the specific medical complications of the underlying disease. Several specific conditions deserve special consideration: Duchenne muscular dystrophy produces progressive scoliosis after the patient becomes non-ambulatory. The disease is also associated with cardiomyopathy and respiratory compromise. Surgical fusion is recommended in many centers when the curve reaches 20- 30° in a patient who has become non-ambulatory; delaying surgery until the curve is larger increases risk because of progressive cardiopulmonary compromise. The fusion is typically T2-pelvis with segmental instrumentation. The advent of corticosteroid therapy (prednisone, deflazacort) has somewhat altered the natural history, slowing the progression and delaying the loss of ambulation, but the role of corticosteroids in delaying scoliosis is uncertain. Spinal muscular atrophy types II and III produce progressive scoliosis. The use of newer therapies including nusinersen, onasemnogene abeparvovec, and risdiplam has substantially altered the natural history; the implications for scoliosis surgery in this population are still being defined. Cerebral palsy scoliosis ranges from mild curves in ambulatory patients to severe pelvic- oblique curves in non-ambulatory GMFCS V patients. The decision for surgery balances the functional improvement in sitting balance and care against the substantial perioperative risk and the underlying medical complexity. Long fusion T2-pelvis with pelvic fixation is the standard.
Adult Scoliosis
Adult scoliosis encompasses adult idiopathic scoliosis (the persistence of adolescent idiopathic scoliosis into adulthood, often with progression) and de novo (degenerative) adult scoliosis (new development of curve in skeletal maturity due to asymmetric degenerative changes). Adult idiopathic scoliosis typically progresses slowly through adult life — approximately 0.5-1° per year on average — and may produce progressive cosmetic, pulmonary, and pain symptoms. Sagittal imbalance (positive sagittal vertical axis with the C7 plumb line passing in front of the femoral heads) is a more important determinant of disability than coronal deformity in this population. De novo (degenerative) adult scoliosis results from asymmetric degenerative disc disease, facet joint arthritis, and rotational subluxation, typically producing a thoracolumbar or lumbar curve with associated stenosis and radicular symptoms. The presentation is typically with back pain, radicular pain, and neurogenic claudication rather than with cosmetic concerns. Surgical management of adult scoliosis is substantially more complex than adolescent surgery, with greater blood loss, longer fusion segments, higher complication rates, and worse outcomes. Indications include progressive deformity, neurological compromise,
intractable pain, and sagittal imbalance. Modern surgical techniques include osteotomies for sagittal deformity correction (pedicle subtraction osteotomy, vertebral column resection), lateral or anterior lumbar interbody fusion for additional correction, and posterior segmental fixation. The complication profile demands careful patient selection, optimization of comorbidities, and detailed informed consent.
Schroth Method and Scoliosis-Specific Exercises
In the past two decades, scoliosis-specific physical therapy methods — particularly the Schroth method developed in Germany — have gained increasing acceptance as adjuncts or alternatives to bracing in mild to moderate adolescent idiopathic scoliosis. The Schroth method combines specific corrective exercises targeting the three-dimensional deformity, postural retraining, and breathing techniques. Evidence for efficacy is growing, with several randomized trials demonstrating improvements in cosmesis, pain, and quality of life, though the effect on radiographic progression is less clear. The method is most commonly used in conjunction with bracing or in the observation range (10-25° curves in skeletally immature patients).
Schroth Method, Bracing Adherence, and Modern Trends
Beyond traditional brace prescription, modern practice increasingly emphasizes adherence monitoring with temperature-sensitive sensors built into braces, which has clarified that compliance is the principal determinant of efficacy and has informed family counseling. Three-dimensional (“3D”) braces — the Rigo brace and others designed using the principles of three-dimensional deformity correction — are gaining popularity, with reports of better in-brace correction than traditional Boston-type braces. Scoliosis-specific physiotherapy, including the Schroth method and the Side-Shift therapy, complements bracing in current practice.
Summary and Take-Home Points
Scoliosis is a heterogeneous disease whose adolescent idiopathic form constitutes the majority of practice in most centers. The clinical recognition by Adam’s forward bend test, the Cobb angle measurement, the Risser staging of skeletal maturity, and the Lenke classification of curve patterns provide the foundation of assessment. Treatment follows a sliding scale: observation for small curves, bracing (with adherence as the key determinant of efficacy) for moderate curves in skeletally immature patients, and surgical posterior fusion with segmental pedicle screw instrumentation for curves over 45-50°. The natural history of untreated adolescent idiopathic scoliosis is variable but predictable from curve magnitude and skeletal maturity; long-term progression in adult life is most concerning for curves over 50° at maturity. Infantile and juvenile idiopathic scoliosis require specific approaches including Mehta casting and growth-friendly surgical techniques. Neuromuscular scoliosis arises from underlying neurological or muscular disease, produces characteristic long C-shaped curves with pelvic obliquity, progresses into adulthood, and requires long instrumented fusion often to the pelvis with substantially higher complication rates. Adult scoliosis — whether persisting from adolescence or arising de novo from asymmetric degeneration — requires individualized assessment of
pain, function, sagittal balance, and surgical risk. Across all forms of scoliosis, the principles of three-dimensional assessment, careful selection of treatment based on age, progression risk, and underlying etiology, and attention to the goals of correction, balance, and stability determine successful outcomes.