Relationship between Quantec measurement and Cobb angle in patients with idiopathic scoliosis

The Quantec Spinal Imaging System (QSIS) is a raster stereography used to measure three-dimensional trunk images. The Q angle, a coronal plane measurement generated by the Quantec Spinal Imaging System (QSIS), was compared with the Cobb angle in assessment of scoliosis curve magnitude. One hundred forty-nine patients with idiopathic scoliosis were evaluated using both the Quantec system and plane radiographs. The Cobb and Q angles demonstrated significant correlation in the thoracic region (r = 0.65, p < 0.05), lumbar region (r = 0.63, p < 0.05), and in the thoracolumbar region (r = 0.70, p < 0.05). The difference between the Q and Cobb angles was small when the Cobb angle was <21 degrees with less than 6 degrees of axial surface rotation, as measured by the QSIS method. For smaller curves with minimal rotation, there is close correlation between the Cobb angle and the Quantec angle.