Reliability Of Cobb Angle Measurements In Severe Congenital Scoliosis

BackgroundThe Cobb angle is commonly used for quantitative assessment of the lateral curvature of the spine in the frontal plane and is usually considered as the golden standard for diagnosis and follow-up of patients with scoliosis. This measurement is also valuable in the planning of surgical procedures, monitoring and management of spine deformities, and determining the severity of the curvature. Because of multiple vertebral malformation in congenital scoliosis, is the measurements with Cobb method reliable and credible? Review of the literature, only refer to two related articles. The first one was published in 1995. The author argued that the intraobserver and interobserver margins of error in measurement are larger than those in AIS. More accurate and precise methods of assessment are needed. Another one published in JBJS demonstrated opposite conclusion against the previous one that the Cobb method was clinically advantageous and appropriate to assess the scoliotic curvature. But in the article, almost all the cases included were less than 90 degrees. Is the Cobb method in X-ray film accurate and reliable in severe congenital scoliosis? In the first part, we chose congenital scoliosis with Cobb angle greater than 90 degrees, and the coronal plane radiographs were measured and analyzed.Three-dimensional and multiplanar reformatted CT imaging allows better visualization and understanding of the deformities of scoliosis and supplementary useful information may be obtained which was obscure or unrecognized with X-ray film, especially for patients with severe deformities. Vertebral anatomy were clearly saw on the three-dimensional and multiplanar reformatted CT imaging, to identify the vertebral endplate, so in theory, the Cobb angle by measuring on the three-dimensional reconstruction of CT may be significantly better than one on the X-ray film. But the CT three-dimensional reconstruction were taken in the supine condition, X-ray films were taken in the standing position. Because of lack of the gravity, the Cobb angle of the spinal deformity was less on the supine position than one on the standing position. We choose severe congenital scoliosis which flexibility is poor. Whether the measurement on the three-dimensional and multiplanar reformatted CT imaging could reflect the severity of scoliosis using the Cobb method or not? We choose 51 severe congenital scoliosis, in order to analysis the reliability of Cobb method on X-ray film or CT scan, and to find a reliable method for measuring severe congenital scoliosis.Part I: Reliability Analysis of The Cobb Angle in Severe Congenital Scoliosis On X-ray FilmMaterial and MethodsOne hundred and forty five patientswere collected from 2012 to 2015. These X-ray films were measured two times by the two senior and experienced doctors. Calculate the average value. Fifty one patients(34 females and 17 males, average age 17.3years) were included, with Cobb angle more than 90 degrees. The same set of fifty one radiographs was measured by five different observers: two highly experienced scoliotic surgeons, one spine surgeon, two traumatic orthopedics doctor. Each observer measured the radiographs twice, with an interval of at least three weeks between the two measurements. Intraclass Correlation Coefficient was assessed comparing intra- and interobserver differences.ResultsThe statistical results for the intraobserver analysis are shown. ICC of observer A is 0.909, observer B 0.892, observer C 0.648, observer D 0.540 and observer E 0.813. ICC between different observers was 0.816.Interobserver difference was analysed. ICC between observer A and B was 0.818. ICC between observer A and C was 0.248. ICC between observer A and D was 0.475. ICC between observer A and E was 0.822. ICC between observer B and C was 0.073. ICC between observer B and D was 0.343. ICC between observer B and E was 0.778. ICC between observer C and D was 0.348. ICC between observer C and E was 0.254. ICC between observer D and E was 0.589.ConclusionThe results showed that Cobb method in severe congenital scoliosis is not as reliable as those in AIS. These margins of error in measurement are large between interobserver and intraobserver, especially for little experienced observer.Part II:Reliability Analysis of The Cobb Angle in Severe Congenital Scoliosis on 3D Reconstruction ImagingMaterial and MethodsThe patients were the same as ones in the previous study. 3D Reconstruction Imaging was necessary. One highly experienced observer not measuring Cobb angle selected one image which showed the coronal main curve distinctly. The same set of fifty one radiographs was measured by five different observers: two highly experienced scoliotic surgeons, one spine surgeon, two traumatic orthopedics doctor. Each observer measured the radiographs twice, with an interval of at least three weeks between the two measurements. Intraclass Correlation Coefficient was assessed comparing intra- and interobserver differences.ResultsThe statistical results for the intraobserver analysis are shown. ICC of observer A is 0.979, observer B 0.978, observer C 0.961, observer D 0.948 and observer E 0.976. ICC between different observers was 0.969. Interobserver difference was analysed. ICC between observer A and B was 0.910. ICC between observer A and C was 0.795. ICC between observer A and D was 0.915. ICC between observer A and E was 0.929. ICC between observer B and C was 0.878. ICC between observer B and D was 0.934. ICC between observer B and E was 0.946. ICC between observer C and D was 0.843. ICC between observer C and E was 0.863. ICC between observer D and E was 0. 939.ConclusionThe results showed that Cobb angle measurements may be reproduced in the 3D Reconstruction Imaging reliably, in similar conditions to those found in clinical practice, suggesting that the digital method is clinically advantageous and appropriate to assess the scoliotic curvature in the frontal plane.