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Scoliosis is a very common problem and many children show some evidence of trunk asymmetry. Clinical significant scoliosis is less common, with one study showing the UK prevalence of curves greater than 20 degrees to be less than 1 in 1000 among children aged 6–14 years.1 Children with spinal deformity attend for outpatient assessment regularly and often undergo repeated radiographic examination. While this is an imaging modality that most doctors are comfortable with there are some problems in its application to spinal deformity.
Curves are described by their appearance on plain films and quantified by the magnitude of the Cobb angle derived from the radiograph. This is the angle subtended between lines drawn along the upper border of the most tilted vertebrae above the curve's apex and the lower border of the most tilted vertebrae below the apex.2 Interpretation of these results is difficult as radiographs represent oblique projections of the twisting spine and the Cobb angle can be seen to vary widely depending on the angle of the beam to the patient.3 In addition significant positioning, and intraobserver and interobserver errors have been observed in calculation of the Cobb angle.4
The child and parents involved are also less concerned with size of the radiographic curve than the magnitude of the perceived deformity, which is very difficult to quantify using radiographs. A large component of the deformity is a result of vertebral rotation causing one side of the trunk to become prominent, producing a rib or loin prominence. While vertebral rotation may be assessed from radiographs, the size of this prominence is less easily defined and as computed tomography (CT) and magnetic resonance imaging (MRI) are performed supine, at present, their exact relation to the erect clinical picture is unclear. All these factors combine, and a …