Use of Artificial Intelligence in Cobb Angle Measurement for Scoliosis: Retrospective Reliability and Accuracy Study of a Mobile App

Abstract

Background: Scoliosis is a spinal deformity in which one or more spinal segments bend to the side or show vertebral rotation. Some artificial intelligence (AI) apps have already been developed for measuring the Cobb angle in patients with scoliosis. These apps still require doctors to perform certain measurements, which can lead to interobserver variability. The AI app (cobbAngle pro) in this study will eliminate the need for doctor measurements, achieving complete automation.

Objective: We aimed to evaluate the reliability and accuracy of our new AI app that is based on deep learning to automatically measure the Cobb angle in patients with scoliosis.

Methods: A retrospective analysis was conducted on the clinical data of children with scoliosis who were treated at the Pediatric Orthopedics Department of the Children's Hospital affiliated with Fudan University from July 2019 to July 2022. Three measurers used the Picture Archiving and Communication System (PACS) to measure the coronal main curve Cobb angle in 802 full-length anteroposterior and lateral spine X-rays of 601 children with scoliosis, and recorded the results of each measurement. After an interval of 2 weeks, the mobile AI app was used to remeasure the Cobb angle once. The Cobb angle measurements from the PACS were used as the reference standard, and the accuracy of the Cobb angle measurements by the app was analyzed through the Bland-Altman test. The intraclass correlation coefficient (ICC) was used to compare the repeatability within measurers and the consistency between measurers.

Results: Among 601 children with scoliosis, 89 were male and 512 were female (age range: 10-17 years), and 802 full-length spinal X-rays were analyzed. Two functionalities of the app (photography and photo upload) were compared with the PACS for measuring the Cobb angle. The consistency was found to be excellent. The average absolute errors of the Cobb angle measured by the photography and upload methods were 2.00 and 2.08, respectively. Using a clinical allowance maximum error of 5°, the 95% limits of agreement (LoAs) for Cobb angle measurements by the photography and upload methods were -4.7° to 4.9° and -4.9° to 4.9°, respectively. For the photography and upload methods, the 95% LoAs for measuring Cobb angles were -4.3° to 4.6° and -4.4° to 4.7°, respectively, in mild scoliosis patients; -4.9° to 5.2° and -5.1° to 5.1°, respectively, in moderate scoliosis patients; and -5.2° to 5.0° and -6.0° to 4.8°, respectively, in severe scoliosis patients. The Cobb angle measured by the 3 observers twice before and after using the photography method had good repeatability (P<.001). The consistency between the observers was excellent (P<.001).

Conclusions: The new AI platform is accurate and repeatable in the automatic measurement of the Cobb angle of the main curvature in patients with scoliosis.

Keywords: artificial intelligence; deep learning; photogrammetry; scoliosis.

Figure 1

Network framework.

Figure 2

Cobb angle measured by the photography method.

Figure 3

Cobb angle measured by the photo upload method.

Figure 4

The mean signed differences between the Picture Archiving and Communication System (PACS) method and the photography method (A) and photo upload method (B).

Figure 5

The mean signed differences between the Picture Archiving and Communication System (PACS) method and photography method for mild scoliosis (A), moderate scoliosis (B), and severe scoliosis (C). The mean signed differences between the PACS method and photo upload method for mild scoliosis (D), moderate scoliosis (E), and severe scoliosis (F). The mean signed differences between the photography method and PACS method for moderate scoliosis with Cobb angles between 25° and 35° (G), and between 35° and 45° (H).

Figure 6

Lenke 5 scoliosis (A), with the upper and lower end vertebrae measured by the Picture Archiving and Communication System (PACS) method being T11 and L4, respectively (B). (C, D) The scoliosis curve depicted by the photo upload method shows that the maximum scoliosis angle is between T12 and L4.