Clinical use of the simple 3D-calculation in scoliosis

In this paper we show the clinical application of a simple method for calculating three-dimensional shape in scoliosis by the use of two tables based on normal standard X-rays in the anteroposterior and lateral projections. The three-dimensional alignment should be considered in both conservative and operative correction. In 57 patients with 87 scoliotic curves we measured the well-known Cobb angle (alpha) and determined the vertebral rotation according to the method of Nash and Moe. We compared this information with the results of the calculated three-dimensional angles of scoliosis (angle beta between the curvature plane and the sagittal plane, angle sigma as the true angle of scoliosis in this curvature plane). In 76 curves (87%) our method was practicable. The true angle sigma is always higher than the projected angle alpha, especially in the clinically relevant range of 20 degrees-40 degrees. Poor correlation is shown between the projected angle alpha and the true angle sigma (r = 0.41 for thoracic curves and r = 0.57 for lumbar curves) and almost no correlation between vertebral rotation and the true angle sigma (r = 0.10 for thoracic curves and r = 0.44 for lumbar curves) and the curvature plane (beta) (r = 0). The three-dimensional shape of scoliosis cannot be estimated by the well-established projected angles and indices and we recommend the use of our simple method for the radiological investigation of scoliotic patients.