Accuracy and applicability of measurement of the scoliotic angle at the frontal plane by Cobb's method, by Ferguson's method and by a new method

Abstract

A new method for the measurement of scoliotic curves in antero-posterior (AP) radiographs is presented, in which the centre of the surface image of the vertebral bodies of the apical and two end vertebrae of the curvature are defined on the basis of geometric principles. Measurements using the Cobb, the Ferguson, and the new method were performed on ten AP radiographs from each of three groups of young patients with right convex thoracic idiopathic scoliosis with Cobb angles of between 7 and 15 degrees, 16 and 45 degrees and 46 and 80 degrees, respectively. Measurements using the Cobb method yielded significantly higher values than measurements using either the Ferguson method or the new method. In curves with Cobb angles of between 7 and 15 degrees, the values using Ferguson's method were significantly lower than those using the new method; the difference increased significantly in curves with a Cobb angle of 16 degrees or more. The level of significance of the intra- and interobserver differences between the new, the Cobb and the Ferguson methods was significantly higher in curves with a Cobb angle of 16 degrees or more. It is argued that measures of the scoliotic angle obtained by the new method are of greater clinical relevance than those obtained by the two other methods. Unlike the Cobb method, the new method takes into consideration the translation of the apical vertebra in relation to the end vertebrae and not only the tilt of the end vertebrae of the curve. As compared to the Ferguson method, the new method is based on standardised geometric principles, and is not influenced by changes in the shape of the vertebral body. Moreover, the repeatability of the new method is greater than that of both the Cobb method and the Ferguson method. Therefore, it is believed that the new method provides a more accurate measure of the scoliotic curve than do the two other methods, and it is to be preferred over the other two methods in longitudinal evaluation of the development of the curve.

Comparison of scoliosis measurements based on three-dimensional vertebra vectors and conventional two-dimensional measurements: advantages in evaluation of prognosis and surgical results

“…Various methods for measuring frontal curvature have been developed like the Greenspan index [1], Diab method [2] or Centroid method [3]. On Ferguson's proposal, the earliest measuring technique evaluated the angle formed by the lines connecting the central points of the upper and lower end-vertebrae of the curve with the central point of the apical vertebra [4].…”

Variability of Manual and Computerized Methods for Measuring Coronal Vertebral Inclination in Computed Tomography Images

“…Such measurements are biased by the selection of the most tilted endplates, errors in drawing lines and systematic errors of inaccurate measuring devices (Capasso et al, 1992). As a result, the reported intra-observer SD between 1.5 • and 8.5 • , and inter-observer SD between 2.5 • and 8.8 • (Chen et al, 2007;Jeffries et al, 1980;Oda et al, 1982;Goldberg et al, 1988;Dutton et al, 1989;Ylikoski and Tallroth, 1990;Carman et al, 1990;Pruijs et al, 1994;Loder et al, 1995;Diab et al, 1995;Shea et al, 1998;Facanha-Filho et al, 2001;Loder et al, 2004;Wills et al, 2007;Gstoettner et al, 2007;De Carvalho et al, 2007;Tanure et al, 2010) span across a relatively large range of values. Adam et al (2005) evaluated the Cobb angle in CT images by extracting reformatted cross-sections, resulting in intra-and inter-observer variability of 3.4 • and 2.7 • SD, respectively.…”

Reliability analysis for manual measurement of coronal plane deformity in adolescent scoliosis. Are 30 × 90 cm plain films better than digitized small films?

“…Studies of inter-observer and intra-observer variability in measurement of this angle [3,7,9,15,16,20] have revealed that errors in radiographic measurements are typically ±5°and are comparable with thresholds of change that can influence treatment decisions [19]. Recent studies [4,5,8,14,18] demonstrate computer-assisted methods to reduce technical errors and the need for memorization of measurement and classification procedures.…”