MEASUREMENT OF VERTEBRAL ROTATION IN ADOLESCENT IDIOPATHIC SCOLIOSIS USING 3-DIMENSIONAL MAGNETIC-RESONANCE-IMAGING

Study Design. This report examines a technique for measurement of axia l vertebral rotation using magnetic resonance imaging. Objectives. To assess the reproducibility of three-dimensional magnetic resonance ima ging in the measurement of vertebral rotation at individual endplates in patients with adolescent idiopathic scoliosis. Summary of Backgroun d Data. Deformity in the sagittal and coronal planes in patients with adolescent idiopathic scoliosis can be readily assessed from plain rad iographs, but the degree of deformity in the axial plane is more diffi cult to determine. Plain film techniques have inherent inaccuracies be cause of loss of definition of anatomic landmarks, and the use of com puted tomography is limited by the high radiation dose associated. Mag netic resonance imaging provides a means of imaging scoliotic deformit y that allows multiplanar reconstruction and that involves no use of i onizing radiation. Methods. Ten patients with adolescent idiopathic sc oliosis were imaged in a Siemens 1-Tesla Impact scanner. Three-dimensi onal volume images of the apical five vertebrae were obtained in the a xial plane and were postprocessed through multiplanar reconstruction. Sections through the superior and inferior endplates of each vertebra were selected in the sagittal and coronal planes, allowing axial recon structions to be obtained in the plane of each endplate. Vertebral rot ation was measured by identifying datum points on the inner surfaces a nd at the junction of the laminas and comparing the angle subtended by these points with a vertical drawn by the computer. Measurements were obtained from the single scanning sequence on two occasions by one ob server and on one occasion by a second observer. Interobserver and int raobserver error was evaluated and correlation with readings obtained from plain films using Perdriolle's torsiometer method assessed. Resul ts. The interobserver variation had a mean of 3.02 degrees (range, 0-1 0 degrees) and a 95% confidence interval of [2.51 degrees, 3.53 degree s]. The intraobserver variation had a mean of 2.56 degrees (range, 0-7 degrees) and a 95% confidence interval of [1.83 degrees, 3.29 degrees ]. The mean difference between measurements obtained :from-magnetic re sonance imaging and plain film was 3.29 degrees (range, 0-12 degrees) with a 95% confidence interval of [1.43 degrees, 5.15 degrees]. Conclu sions. The degree of vertebral rotation can be accurately and reproduc ibly assessed by three-dimensional sional magnetic resonance imaging. Measurements can be made through individual endplates that allow asses sment of the relative amount of intervertebral and intravertebral defo rmity.