Clinical use of the simple 3D-calculation in scoliosis

Abstract

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 wellknown Cobb angle (a) 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 β between the curvature plane and the sagittal plane, angle σ as the true angle of scoliosis in this curvature plane). In 76 curves (87%) our method was practicable. The true angle σ is always higher than the projected angle α, especially in the clinically relevant range of 20°–40°. Poor correlation is shown between the projected angle a and the true angle σ (r = 0.41 for thoracic curves and r = 0.57 for lumbar curves) and almost no correlation between vertebral rotation and the true angle σ (r = 0.10 for thoracic curves and r = 0.44 for lumbar curves) and the curvature plane (β) (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.