Assessing the child with scoliosis: the role of surface topography.

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. 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. Interpretation of these results is diYcult 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. In addition significant positioning, and intraobserver and interobserver errors have been observed in calculation of the Cobb angle. 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 diYcult 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 clinician can have no clear picture of what the deformity of a patient with an observed Cobb angle of 30 degrees will actually be. A curve of 60 degrees will not be twice as bad as a curve of 30 degrees and a surgical correction of 50% according to the Cobb angle may not halve the deformity. Even when using low dose postero-anterior and lateral radiographs, concern exists about the repeated exposure of children to ionising radiation. Recent work has suggested significant excess in breast cancer deaths, with a standardised mortality ratio of 4.1 for a woman receiving 50 or more radiographs, with a lag time of 30 years. 6 Clearly a safe, reliable, truly three dimensional investigation would be highly useful in the assessment of the child with scoliosis.