What are the different types of scoliosis and how do they appear on X-ray (X-radiation)?

Types of Scoliosis and X-ray Appearance

Scoliosis is classified into four major etiologic types—idiopathic, congenital, neuromuscular, and degenerative—with upright PA and lateral spine radiographs serving as the primary imaging modality to visualize lateral curvature ≥10° with vertebral rotation. 1

Classification by Etiology

Idiopathic Scoliosis

• Adolescent idiopathic scoliosis (10-18 years) constitutes 75-80% of all scoliosis cases and is the most common type encountered in clinical practice. 1
• Juvenile idiopathic scoliosis (4-9 years) represents approximately 8% of the idiopathic population. 1
• This is a diagnosis of exclusion, occurring in the absence of vertebral anomalies or associated syndromes. 1
• Female predominance is marked, with a 10:1 female-to-male ratio for curves exceeding 40°. 1

Congenital Scoliosis

• Results from vertebral anomalies present at birth, including hemivertebrae and other bony malformations. 1
• Curves with contralateral hemivertebra may progress more than 10° per year. 1
• Intraspinal anomalies occur in 28% of patients with isolated hemivertebra and 43% in surgical cases, including tethered cord, filar lipoma, syringohydromyelia, and diastematomyelia. 1

Degenerative (Adult) Scoliosis

• Primary degenerative scoliosis develops from asymmetric disc and facet joint arthritis in skeletally mature patients, often classified as "de novo" scoliosis. 2
• Typically presents with back pain and may be accompanied by spinal stenosis symptoms. 2
• Progression is supported by osteoporosis, particularly in post-menopausal females. 2

Secondary Scoliosis

• Develops in the context of oblique pelvis (leg length discrepancy, hip pathology), metabolic bone disease, or as secondary curves in neuromuscular and syndrome-related conditions. 2, 3

X-ray Appearance and Key Radiographic Features

Standard Imaging Protocol

• Upright PA (posteroanterior) and lateral spine radiographs are the primary imaging modality for diagnosis, classification, and treatment planning. 1, 4
• PA views are preferred over AP to reduce breast radiation exposure. 1
• Radiographs must visualize the cervical, thoracic, and lumbar spine to assess the complete spinal alignment. 1

Critical Radiographic Measurements

Cobb Angle Measurement:

• Defines scoliosis as lateral spinal curvature with Cobb angle ≥10°. 5, 6
• Measured by drawing lines parallel to the superior endplate of the uppermost tilted vertebra and inferior endplate of the lowermost tilted vertebra; the angle between perpendiculars to these lines is the Cobb angle. 5
• This measurement is critical for surgical decision-making and monitoring progression. 7

Vertebral Rotation (Nash-Moe Method):

• Scoliosis involves both lateral curvature and vertebral rotation, which must be assessed. 5, 6
• The Nash-Moe method grades rotation based on the position of the pedicles relative to the vertebral body margins. 5

Key Vertebral Landmarks:

• Apex vertebra: The most laterally deviated vertebra in the curve. 5
• End vertebrae: The uppermost and lowermost vertebrae that tilt maximally into the concavity of the curve. 5
• Neutral vertebra: The vertebra with minimal rotation. 5
• Stable vertebra: The vertebra bisected by the central sacral vertical line. 5

Curve Pattern Recognition

Typical vs. Atypical Patterns:

• Right thoracic curves are typical for adolescent idiopathic scoliosis; left thoracic or thoracolumbar curves are atypical red flags requiring investigation for neural axis pathology. 4, 8
• Left-sided curves warrant immediate MRI evaluation, as 2-4% of patients diagnosed with idiopathic scoliosis actually have neural axis abnormalities causing the deformity. 8

Structural vs. Nonstructural Curves:

• Structural curves demonstrate vertebral rotation and do not correct on side-bending radiographs. 5
• Nonstructural (compensatory) curves lack significant rotation and correct with side-bending. 5

Congenital Scoliosis-Specific Findings

• PA and lateral radiographs identify vertebral anomalies including hemivertebrae, block vertebrae, and segmentation failures that differentiate congenital from idiopathic scoliosis. 1
• CT with multiplanar and 3-D volume rendered reformatted images provides superior visualization of bony malformations and aids presurgical planning. 1, 4

Skeletal Maturity Assessment

• Risser sign (ossification of the iliac apophysis) is evaluated on PA radiographs to assess skeletal maturity and predict progression risk. 7
• Skeletally immature patients with Cobb angles >20° have progression likelihood exceeding 70%. 1

Serial Monitoring Recommendations

• The American College of Radiology recommends limiting spine radiographs to once every 12 months for adolescents at Risser stages 0-3 and every 18 months for Risser stages 4-5. 7
• SOSORT guidelines suggest no more than once every 6 months for serial follow-up. 1
• After skeletal maturity, only curves >30° require monitoring for progression. 5

Critical Pitfalls to Avoid

• A negative neurologic examination does not predict a normal MRI; history and physical examination demonstrate only 62% accuracy for diagnosing intraspinal anomalies with hemivertebra. 1
• Left thoracic curves, short segment curves, absence of apical segment lordosis, rapid progression (>1° per month), functionally disruptive pain, and focal neurological findings are red flags requiring MRI evaluation before attributing scoliosis to idiopathic causes. 4, 8
• Neural axis abnormalities occur in more than 20% of patients with severe curves, and MRI of the entire spine is mandatory before surgical intervention. 7, 8
• Clinical examination alone cannot determine exact curve magnitude, classify scoliosis type, or evaluate progression—radiography is essential. 4