Comparison of Cobb Angles in Idiopathic Scoliosis on Standing Radiographs and Supine Axially Loaded MRI


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Abstract

Study Design.Prospective, patient controlled.Objective.To compare Cobb angles in idiopathic scoliosis between standing radiographs and a nonradiographic procedure.Summary of Background Data.Repeated radiographic examinations at young age may increase the risk for breast cancer in adulthood. MRI images the spine satisfactorily but is cumbersome in standing. A harness supplying axial load to a lying subject simulates the standing radiograph appearance of the lumbar spine.Methods.Thirty patients with idiopathic scoliosis greater than 20° performed a routine posteroanterior and lateral standing thoracolumbar spine radiograph and an MRI in supine position without and with axial loading.Results.Mean Cobb angle for the major curve was 31° on standing radiographs, 23° on nonloaded supine MRI, and 31° on supine loaded MRI. Axially loaded, compared with nonloaded, MRI increased the Cobb angle by 8°. The mean difference between standing radiograph and supine axially loaded MRI was 0°, with an intermethodologic variation(s) of 3.4°. Radiographic and MRI (axially loaded) Cobb angles correlated positively (r = 0.78).Conclusions.Axial loading on supine MRI produces coronal Cobb angles similar to standing radiographs. This is a way to acquire reliable Cobb angles without radiation in the monitoring of idiopathic scoliosis.

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