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Eur J Orthop Surg Traumatol. 2016 Jan;26(1):53-7. doi: 10.1007/s00590-015-1701-7. Epub 2015 Sep 16.

Reliability analysis of Cobb angle measurements of congenital scoliosis using X-ray and 3D-CT images.

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Department of Orthopedics and Spine Surgery, Meijo Hospital, 1-3-1, Sannomaru, Naka-ku, Nagoya, 460-0001, Japan.
Department of Orthopedic Surgery, Shriners Hospitals for Children-Philadelphia, Philadelphia, PA, USA.
Division of Orthopaedics, Children's Hospital of Philadelphia, Philadelphia, PA, USA.
Department of Pediatric Orthopaedic Surgery, Hospital la Conception, San German, PR, USA.
Department of Orthopaedic Surgery, Children's Hospital Boston, Boston, MA, USA.
Division of Pediatric Orthopaedics, Isaac Walton Killam Health Centre, Halifax, NS, Canada.
Department of Orthopaedic Surgery, Emory University School of Medicine, Emory Spine Center, Atlanta, GA, USA.
Department of Orthopaedic Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan.
South Texas Spinal Clinic, San Antonio, TX, USA.
Department of Pediatric Orthopaedic Surgery, Columbia University Medical Center, New York, NY, USA.
Campbell Clinic, University of Tennessee, Memphis, TN, USA.
Department of Orthopaedics, University of Utah, Salt Lake City, UT, USA.
Department of Orthopedics and Spine Surgery, Meijo Hospital, 1-3-1, Sannomaru, Naka-ku, Nagoya, 460-0001, Japan.



Therapeutic decisions for congenital scoliosis rely on Cobb angle measurements on consecutive radiographs. There have been no studies documenting the variability of measuring the Cobb angle using 3D-CT images in children with congenital scoliosis. The purpose of this study was to compare the reliability and measurement errors using X-ray images and those utilizing 3D-CT images.


The X-ray and 3D-CT images of 20 patients diagnosed with congenital scoliosis were used to assess the reliability of the digital 3D-CT images for the measurement of the Cobb angle. Thirteen observers performed the measurements, and each image was analyzed by each observer twice with a minimum interval of 1 week between measurements. The analysis of intraobserver variation was expressed as the mean absolute difference (MAD) and standard deviation (SD) between measurements and the intraclass correlation coefficient (IaCC) of the measurements. In addition, the interobserver variation was expressed as the MAD and interclass correlation coefficient (IeCC).


The average MAD and SD was 4.5° and 3.2° by the X-ray method and 3.7° and 2.6° by the 3D-CT method. The intraobserver and interobserver intraclass ICCs were excellent in both methods (X-ray: IaCC 0.835-0.994 IeCC 0.847, 3D-CT: IaCC 0.819-0.996 IeCC 0.893). There was no significant MAD difference between X-ray and 3D-CT images in measuring each type of congenital scoliosis by each observer.


Results of Cobb angle measurements in patients with congenital scoliosis using X-ray images in the frontal plane could be reproduced with almost the same measurement variance (3°-4° measurement error) using 3D-CT images. This suggests that X-ray images are clinically useful for assessing any type of congenital scoliosis about measuring the Cobb angle alone. However, since 3D-CT can provide more detailed images of the anterior and posterior components of malformed vertebrae, the volume of information that can be obtained by evaluating them has contributed greatly to the development of strategies for the surgical treatment of congenital scoliosis.


Children; Cobb angle; Computed tomography; Congenital scoliosis; Interobserver; Intraobserver; Measurement reliability; X-ray

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