Intra- and Interrater Reliability of Cobb Angle Measurements on the Plane of Maximum Curvature Using Ultrasound Imaging Method

Abstract Study Design Retrospective reliability study. Objectives To investigate the intra- and interrater reliability of Cobb angle measurements on the plane of maximum curvature (PMC) using ultrasound (US) images on children with adolescent idiopathic scoliosis (AIS). Summary of Background Data Cobb angle measurement on posteroanterior (PA) radiographs is the gold standard to assess curve severity. However, the PA Cobb angle does not reflect the true three-dimensional deformity. Methods One hundred one children with AIS (87 F; 14 M) (age: 13.7 ± 1.7 years) were recruited and 157 curves were recorded by clinicians on radiographs. Three raters, R1, R2, and R3 with 0, 4, and 20+ years of experience, respectively, measured the PA Cobb, vertebral axial rotation (VAR), PMC Cobb, and PMC orientations on US images. The true PMC orientations were determined using 3D reconstructions on the PA and lateral EOS radiographs. The reliability of R1 measurements on PMC orientations were validated using intermethod (US vs. EOS measurements) with the intraclass correlation coefficients (ICCs). Inter- and intrarater reliabilities, standard error measurements, and Bland-Altman’s bias were used to report the PMC Cobb and VAR measurements. Results Intermethod, inter-, and intrarater ICC(2,1) values for all reliability assessments were greater than 0.9. The mean absolute differences and the standard error measurements for both PMC Cobb and VAR were less than 4° and 0.5°, respectively. The PMC orientation was strongly correlated (r 2 = 0.88) between both measurement modalities. There appeared to be a positive association between the difference of PMC and PA Cobb when the PA Cobb and the maximum VAR were greater than 30° and 14°, respectively. Conclusion The PMC Cobb and VAR can be measured reliably on US images. Future studies should validate the PMC Cobb angle and to include a wider Cobb angle range on participants.