Comparison of two- and three-dimensional measurement of the Cobb angle in scoliosis

Ricarda Lechner,Dietmar Dammerer,Martin Thaler,Michael Liebensteiner,Christian Bach,David Putzer

doi:10.1007/s00264-016-3359-0

Ricarda Lechner, Dietmar Dammerer + Show 4 more

Open Access

https://doi.org/10.1007/s00264-016-3359-0

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Abstract

PurposeThe Cobb angle as an objective measure is used to determine the progression of deformity, and is the basis in the planning of conservative and surgical treatment. However, studies have shown that the Cobb angle has two limitations: an inter- and intraobserver variability of the measurement is approximately 3–5 degrees, and high variability regarding the definition of the end vertebra. Scoliosis is a three-dimensional (3D) pathology, and 3D pathologies cannot be completely assessed by two-dimensional (2D) methods, like 2D radiography. The objective of this study was to determine the intraobserver and interobserver reliability of end vertebra definition and Cobb angle measurement using X-rays and 3D computer tomography (CT) reconstructions in scoliotic spines.MethodsTo assess interoberver variation the Cobb angle and the end vertebra were assessed by five observers in 55 patients using X-rays and 3D CT reconstructions. Definition of end vertebra and measurement of the Cobb angle was repeated two times with a three-week interval. Intraclass correlation coefficients (ICC) were used to determine the interobserver and intraobserver reliabilities. 95% prediction limits were provided for measurement errors.ResultsIntraclass correlation coefficient (ICC) showed excellent reliability for both methods. The measured Cobb angle was on average 9.2 degrees larger in the 3D CT group (72.8°, range 30–144) than on 2D radiography (63.6°, range 24–152).ConclusionsIn scoliosis treatment it is very essential to determine the curve magnitude, which is larger in a 3D measurement compared to 2D radiography.

Highlights

Accuracy and consistency are crucial in the radiographic assessment of scoliosis
Scoliosis is a threedimensional (3D) deformity, whereas the Cobb angle measured in a plane X-ray is a two-dimensional (2D) value. 3D pathologies cannot be completely assessed by 2D methods, like radiography
For the definition of end vertebrae and Cobb angle, the intraobserver Intraclass correlation coefficients (ICC) was excellent in the radiographs and in the 3D reconstructions, except for the definition of the lower end vertebra of observer 2 in the 3D reconstructions (Table 3)

Summary

Introduction

Accuracy and consistency are crucial in the radiographic assessment of scoliosis. The findings of these measurements have significant implications for the treatment and management of patients [1]. Studies of interobserver and intraobserver reliability in measurement of the Cobb angle have shown a measurement error of approximately 3–5° [3,4,5,6]. Scoliosis is a threedimensional (3D) deformity, whereas the Cobb angle measured in a plane X-ray is a two-dimensional (2D) value. Accurate measurement of the radiological extent of the deformity is hardly possible. The aim of our study was to investigate Cobb angle measurement in 3D reconstructed images of the spine and to compare them with conventional supine radiographs, as well as to determine the interobserver and intraobserver variability associated with both techniques

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