Quantification of skeletal, muscular and kinematics parameters in scoliosis : methodological and clinical studies

This dissertation presents new methods derived for precise evaluation of a number of anatomical and functional variables of the complex thoracospinal deformity in scoliosis. By consensus the scoliotic angle at the frontal plane is measured on radiographs using the Cobb method. Another way of measuring this angle, the Ferguson method, although evidently more accurate than the Cobb, is not in use. The Cobb method uses only the declination of the upper and the lower vertebra of the curve to measure the degree of the curve. The Ferguson method uses the centroid of these two vertebrae and of the apical one to define the angle. In a derived new method the geometrical, i.e., the true, centre of the three vertebrae is defined on antero-posterior radiographs of the spine to delineate the scoliotic angle. Comparison of the measurements by the three methods in three groups of radiographs with different degrees of scoliosis shows that the new method gives higher accuracy and better repeatability than the two other methods. Studies on the vertebral growth under normal and pathological conditions are based on measurements of the vertebral height at different points of interest on radiographs, since there is no method for evaluation of the vertebral volume. A new stereological method is presented which allows estimation of the vertebral volume in vivo. The volume of one isolated normal and one scoliotic vertebra was measured in a model study using frontal and lateral radiographs and one CT-scan of each. The height of the vertebrae was measured at five points on the radiographs and was expressed as weighted circumferential height. Then the area of the vertebral body was measured using a grid on the CT-scan of the vertebra and the volume was calculated using the Cavallieri method. The accuracy of the measurements with the new method was high compared with serial CT-scans of the whole vertebra. The applicability of the method was evaluated in a series of scoliotic patients who had undergone posterior spinal instrumentation and fusion. The results showed that the weighted circumferential height of the three vertebrae had increased significantly at the last follow up on average 3 years after the operation. Also the volume of the apical vertebra was found to have increased, though not significantly. It is concluded that the proposed method provides accurate evaluation of vertebral body volume changes. The role of the intercostal muscles in the development of the thoracospinal