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Imaging in scoliosis
  1. ROSALIND J JEFFERSON, Specialist Registrar, Department of Paediatrics
  1. Wycombe General Hospital
  2. High Wycombe, UK

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    Editor,—I read with interest the article “Imaging in scoliosis”. In addition to the radiological techniques described, I would include surface shape measurement as a simple, safe, repeatable, and clinically relevant assessment.

    Associated with the bony deformity there is a cosmetic problem; indeed, idiopathic scoliosis is primarily a cosmetic disorder. The first sign commonly noticed by the clinician or patient is an asymmetry of backshape, resulting from axial rotation of the spine and rib cage. Treatment is aimed at the reversal or arrest of the progression of this visible deformity as well as that of the underlying skeletal abnormality.

    Quantitative assessment of scoliosis is necessary both to assess the severity of the condition, and to monitor its progression. The Cobb angle is a reasonably consistent uniplanar measure of spinal deformity, but indicates neither the vertebral rotation/rib prominence which causes the cosmetic deformity, nor any associated changes in kyphosis/lordosis, thus representing only a partial record of the overall disease.

    Methods of evaluating back shape or cosmetic deformity in scoliosis include measurement of simple parameters such as the height difference between left and right sides of the back during the forward bend test. However, they too attempt to reduce a complex three dimensional shape to a single number which inadequately represents the full clinical deformity. Furthermore, being posture dependent, the consistency of measurement is poor.

    An advancement involves optical measurement techniques, with the advantage of avoiding contact with the patient. The Moire fringe technique1 produces an instant graphical representation of the whole back, rather like a contour map, but even a small movement of the subject causes the appearance of the picture to change dramatically. The integrated shape imaging system (ISIS) shape measurement and analysis system2 uses totally safe visible light to scan the back in one second and produces a printed computer analysis of three dimensional backshape within five minutes. Patient posture is not critical and the system can be operated in a normal office environment. An ISIS scan provides the clinician with a repeatable objective assessment of the surface shape of the back in three planes, and consecutive scans can be examined for any indication of progression. Used as a regular screening aid, it has been estimated to reduce the number of spinal radiographs, and thus radiation dose, by as much as 75%. Chief indications for radiographs become at initial presentation to exclude bony anomalies, preoperatively to assess fusion levels, and postoperatively to check instrumentation and fission mass.

    Although the exact relation between back surface shape and skeletal deformity is not well defined, surface shape measurements such as ISIS have been shown to be valuable in assessing the progression of a scoliotic curve, the effect of treatment on backshape, and in giving a reliable indication of the need for spinal surgery.3

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