= presence of ≥1 lateral curves of the vertebral column in the coronal plane with a Cobb angle of ≥10°

◊A curve of <10° represents spinal asymmetry and NOT scoliosis, is asymptomatic and nonprogressive!

Mechanism: rotation of vertebrae in axial plane → discrepant axial loading between ventral + dorsal portions

Etiology:

1. PRIMARY = idiopathic (80%)
   1. Infantile (0–3 yrs.): M÷F=3.5÷1; levoscoliosis; self-limited
   2. Juvenile (4–10 yrs.): progression in 70–95%
   3. Adolescent (11–18 yrs.): M÷F=1÷4; dextroscoliosis; progression in 5%
2. SECONDARY
   1. congenital (10%) with progression in 75%
      1. Osteogenic: wedge-shaped vertebra, hemivertebra, fused vertebra, unilateral bar
      2. Neuropathic: tethered cord, syringomyelia, Chiari malformation, (myelo)meningocele, diastematomyelia
   2. developmental
      1. Skeletal dysplasia: achondroplasia
      2. Skeletal dysostosis: neurofibromatosis, osteogenesis imperfecta
      3. Degenerative scoliosis
      4. Traumatic scoliosis
   3. neuromuscular
      1. Neuropathic (acquired): cerebral palsy, spinocerebellar degeneration, poliomyelitis
      2. Myopathic: muscular dystrophy
   4. tumor-associated
      1. Osseous: osteoid osteoma, osteoblastoma
      2. Extraosseous: extramedullary (eg, neurofibroma) / intramedullary (eg, astrocytoma) tumor

A focal short-segment scoliosis or painful scoliosis should raise suspicion for an underlying lesion.

Nomenclature:

• apex = vertebra / disk with the greatest rotation / farthest deviation from center of vertebral column
• end vertebra = vertebra with maximum tilt toward apex of curvature; used to measure Cobb angle
• neutral vertebra = vertebra without rotation (= symmetric pedicles) on standing frontal radiograph
• stable vertebra = vertebra farthest cephalad roughly bisected by CSVL below end vertebra of distal curve
• CSVL = central sacral vertical line = line drawn perpendicular to tangential line across iliac crests bisecting sacrum
• Primary and Secondary Curves
  • Major curve = primary structural curve with a Cobb angle of >25° on ipsilateral bending; largest abnormal curve that develops first; not correctable with ipsilateral bending
    
  • Minor curve = secondary nonstructural compensatory smaller curve that develops later by repositioning the head and trunk over pelvis to maintain balance; correctable with ipsilateral bending
• Vertebral Balance
  • Plumb line = vertical line drawn downward from center of C7 parallel to lateral edge of radiograph
  • Coronal imbalance = distance between CSVL + plumb line >2 cm on frontal x-ray; plumb line to right (left) of CSVL = positive (negative) imbalance
  • Sagittal imbalance = distance between posterosuperior aspect of S1 + plumb line >2 cm on lateral x-ray; plumb line anterior (posterior) to S1 = positive (negative) imbalance
• Vertebral Rotation (Nash-Moe method)

Cobb angle: angle formed by intersection of 2 lines parallel to endplates of superior + inferior end vertebrae or intersection of the 2 lines drawn perpendicular to the endplate lines

• Accuracy: ± 5°
• Progressive curve: angle increase of ≥5°
• Limitation: 2-D radiograph describing a 3D deformity with vertebral rotation
• Pitfalls: diurnal variation of 5° (worse in afternoon); 2–7° measurement error; 5–10° interobserver error; actual angle may be 20% greater than plotted depending on accuracy + reproducibility of patient positioning on frontal x-ray

Progression: parallels spinal growth; after skeletal maturity at <30° no progression, at 30–50° increase by 10–15° per year, at 50–75° increase by 1° per year

Prognosis: with Cobb angle >50° higher rate of back pain + mortality associated with cardiopulmonary Cx