What Is the Actual 3D Representation of the Rib Vertebra Angle Difference (Mehta Angle)?. Issue 2 (15th January 2018)

• Record Type: Journal Article
• Authors: Brink, Rob C.; Schlösser, Tom P.C.; van Stralen, Marijn; Vincken, Koen L.; Kruyt, Moyo C.; Chu, Winnie C.W.; Cheng, Jack C.Y.; Castelein, René M.
• Is Part Of: Spine. Volume 43:Issue 2(2018)
• Publication Date: 2018-01-15
• Subjects: adolescent idiopathic scoliosis -- Mehta angle -- rib vertebra angle difference -- RVAD -- three-dimensional analysis; Spine -- Abnormalities -- Periodicals; Spine -- Diseases -- Periodicals; Spine -- Surgery -- Periodicals; 616.73005
• DOI: 10.1097/BRS.0000000000002225
• Languages: English
• ISSNs: 0362-2436

Abstract

Abstract : Study Design: Cross-sectional study. Objective: To establish the relevance of the conventional two-dimensional (2D) rib vertebra angle difference (RVAD) and the relationship with the complex three-dimensional (3D) apical morphology in scoliosis. Summary of Background Data: The RVAD, also known as Mehta angle, describes apical rib asymmetry on conventional radiographs and was introduced as a prognostic factor for curve severity in early onset scoliosis, and later applied to other types of scoliosis as well. Methods: An existing idiopathic scoliosis database of high-resolution computed tomography scans used in previous work, acquired for spinal navigation, was used. Eighty-eight patients (Cobb angle 46°–109°) were included. Cobb angle and 2D RVAD, as described by Mehta, were measured on the conventional radiographs and coronal digitally reconstructed radiographs (DRR) of the prone computed tomography scans. A previously validated, semiautomatic image processing technique was used to acquire complete 3D spinal reconstructions for the measurement of the 3D RVAD in a reconstructed true coronal plane, axial rotation, and sagittal morphology. Results: The 2D RVAD on the x-ray was on average 25.3° ± 11.0° and 25.6° ± 12.8° on the DRR ( P = 0.990), but in the true 3D coronal view of the apex, hardly any asymmetry remained (3D RVAD: 3.1° ± 12.5°; 2D RVAD on x-ray and DRR vs. 3D RVAD: P < 0.001). 2D apical rib asymmetry in the anatomical coronal plane did not correlate with the same RVAD measurements in the 3D reconstructed coronal plane of the rotated apex ( r = 0.155; P = 0.149). A larger 2D RVAD was found to correlate linearly with increased axial rotation ( r = 0.542; P < 0.001) and apical lordosis ( r = 0.522; P < 0.001). Conclusion: The 2D RVAD represents a projection-based composite radiographic index reflecting the severity of the complex 3D apical morphology including axial rotation and apical lordosis. It indicates a difference in severity of the apical deformation. Level of Evidence: 4