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Chapter Summary
• Context: Idiopathic scoliosis is the most common form of structural scoliosis and remains a diagnosis of exclusion. Before attributing a spinal curve to an idiopathic etiology, congenital, neuromuscular, syndromic, and other systemic causes must be thoroughly ruled out. Its underlying etiology remains unknown and is likely multifactorial, involving genetic susceptibility and complex interactions among growth, biomechanical, neurological, hormonal, and metabolic factors. Curve progression is non-uniform and depends primarily on curve magnitude, structural pattern, and remaining skeletal growth. Therefore, comprehensive evaluation must integrate physical examination, skeletal maturity staging, and standardized full-spine radiographs, with prompt recognition of atypical features that warrant detailed neuraxis MRI. In surgical management, angular correction represents only one component of the goal. Coronal and sagittal balance, direct axial derotation, shoulder level symmetry, and preserving the maximum number of mobile lumbar segments are critical to achieving durable, functional long-term outcomes.
• Chapter Objective: To present an integrated approach to idiopathic scoliosis, covering diagnosis, epidemiology, natural history, clinical and radiographic evaluation, and the Lenke classification system. The reader will master factors predictive of progression, appropriately select observation or conservative bracing protocols, recognize clinical indications for surgery, plan selective fusion levels, and critically evaluate the indications and limitations of growth modulation and preservation techniques.
• Diagnosis and natural historyIdiopathic scoliosis must be recognized as a complex three-dimensional spinal and thoracic deformity, diagnosed only after thorough clinical, neurological, and radiographic evaluation excludes other etiologies. The chapter reviews chronological subdivisions (infantile, juvenile, and adolescent idiopathic scoliosis). Progression risk depends heavily on the interplay between curve magnitude and remaining skeletal growth. Thoracic and double structural patterns exhibit the greatest propensity for progression, particularly during the peak pubertal growth spurt. Following skeletal maturity, progression typically slows and is determined primarily by residual curve magnitude.
• Clinical examinationAsymmetry of shoulders, scapulae, waistline, flank creases, and trunk balance are classic presentations. The Adams forward bend test and scoliometer measurement evaluate rotational prominence (Figure 4). Disproportionate back pain, neurological deficits, or atypical curve geometry must trigger an immediate search for secondary etiologies. A comprehensive neurological examination is mandatory. The chapter emphasizes heightened vigilance for atypical left thoracic curves, rapid progression, or findings suggestive of underlying neuraxis malformations.
• Imaging and 3D interpretationFull-spine standing biplanar radiographs form the cornerstone of diagnostic imaging. They must permit precise characterization of curve magnitude, coronal and sagittal global balance, vertebral rotation, skeletal maturity (Risser sign, triradiate cartilage), and reference vertebrae identification. The Cobb angle remains the clinical standard, despite known measurement variability and its 2D projection of a 3D deformity. Lateral bending, traction, and push-prone radiographs are reserved for surgical planning to assess curve flexibility. Neuraxis MRI is performed selectively when non-idiopathic or atypical features are suspected.
• The Lenke classification systemThe Lenke classification categorizes adolescent idiopathic scoliosis according to curve pattern (types 1 to 6), lumbar modifier (A, B, C), and thoracic sagittal profile (hypokyphotic, normal, hyperkyphotic), illustrated in Figures 8 through 12. Its primary strength lies in standardizing anatomical communication and guiding surgical fusion levels by clearly differentiating structural from non-structural compensatory curves. The authors emphasize that while Lenke is a 2D system, the actual deformity is multiplanar.
• Management and motion preservationA large proportion of mild curves can be safely observed, while bracing plays a central role in skeletally immature patients at high risk of progression. Surgical intervention is indicated through a multifactorial assessment combining progression, maturity, curve severity, trunk balance, and cosmetic impact. When indicated, instrumentation should fuse all structural curves while sparing non-structural compensatory curves whenever safe. The selection of upper and lowest instrumented vertebrae aims to optimize 3D correction while preserving lumbar motion. Figures 18–24 detail selective thoracic fusion criteria, avoiding distal adding-on. Finally, the chapter discusses anterior vertebral body tethering as an emerging non-fusion growth modulation technique for selected immature patients, noting the need for rigorous selection and long-term surveillance.
• Clinical Application: In clinical practice, the initial step is verifying that the scoliosis is truly idiopathic. History, physical inspection, Adams test, scoliometer, detailed neurological examination, and standing whole-spine radiographs must present a fully coherent picture. Severe pain, midline cutaneous lesions, hyperreflexia, absent abdominal reflexes, or left thoracic curves warrant brain and whole-spine MRI before proceeding. Once an idiopathic diagnosis is confirmed, the central question is progression risk, determined by synthesizing current Cobb angle with skeletal maturity (Risser stage, Sanders score). Skeletally immature patients with curves between 20° and 40° benefit from rigid, compliant bracing and regular follow-up. In surgical candidates, the Lenke classification provides a structural roadmap, but does not operate alone. Shoulder balance, trunk plumbline, flexibility radiographs, sagittal thoracic kyphosis, and lumbosacral relationships must guide fusion levels. Preserving distal lumbar motion is vital, but selective thoracic fusion must be avoided if the lumbar curve is stiff, unbalanced, or structurally dominant, which risks coronal decompensation and distal adding-on. Direct vertebral rotation maneuvers correct axial rib hump without requiring extensive thoracoplasty. Growth modulation options like vertebral body tethering represent specialized alternatives that demand strict skeletal maturity criteria and realistic family counseling regarding revision rates.
