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A Computer-aided Cobb Angle Measurement Method and its Reliability

Zhang, Junhua PhD*; Lou, Edmond PhD; Shi, Xinling MSc*; Wang, Yuanyuan PhD; Hill, Douglas L. MBA; Raso, James V. MASc; Le, Lawrence H. PhD§; Lv, Liang MM

doi: 10.1097/BSD.0b013e3181bb9a3c
Original Articles

Study Design Development of a computer-aided Cobb measurement method and evaluation of its reliability.

Objectives To reduce the variability of Cobb angle measurement by developing the computer-aided method and to investigate if the developed method is sensitive to observer skill levels or experiences.

Summary of Background Data Therapeutic decisions for scoliosis heavily rely on the Cobb angle measured from consecutive radiographs. The manual Cobb measurement is subject to human errors. The observer error is 3 to 10 degrees resulted from different end-vertebrae selection and/or manually drawing variable best-fit lines to the endplates of the end-vertebrae.

Methods A fussy Hough transform technique was used to develop a computer-aided method to detect the vertebral endplates. The Cobb angle, upper end-vertebra, and lower end-vertebra were then measured automatically. The computer-aided method was tested twice by each of 3 observers in 84 posteroanterior radiographs from patients with adolescent idiopathic scoliosis. The intraobserver and interobserver errors were analyzed.

Results Both the intraobserver and interobserver reliability analyses resulted in the intraclass correlation coefficients higher than 0.9 for the Cobb angle. The average intraobserver and interobserver errors were less than 3 degree for the Cobb angle, and less than 0.3 levels for both the upper and lower end-vertebral identification. There were no significant differences in the measurement variability between groups of curve location (thoracic, thoracolumbar, and lumbar), curve direction (right and left), curve magnitude (curves less than 25 degree, between 25 and 45 degrees, and more than 45 degree), and observer experience (experienced observer and inexperienced observers).

Conclusions Compared with the documented results, variability of the Cobb measurement is reduced by using the developed computer-aided method. This method can help orthopedic surgeons measure the Cobb angle more reliably during scoliosis clinics.

*Department of Electronic Engineering, Yunnan University, Yunnan, China

Department of Rehabilitation Technology, Glenrose Rehabilitation Hospital, Alberta, Canada

Department of Electronic Engineering, Fudan University, Shanghai, China

§Department of Radiology and Diagnostic Imaging, University of Alberta, Alberta, Canada

Department of Radiology, the First People's Hospital of Yunnan Province, Yunnan, China

Supported by the General Program of Basic Applied Research of Yunnan Province (2008CD079).

Reprints: Junhua Zhang, PhD, Department of Electronic Engineering, Yunnan University, No. 2 Cuihu Road, Kunming 650091, China (e-mail:

Received for publication May 28, 2009

accepted August 5, 2009

© 2010 Lippincott Williams & Wilkins, Inc.