Reliability of the measurement of thoracolumbar burst fracture kyphosis with Cobb angle, Gardner angle, and sagittal index

Introduction Kyphotic deformity plays a key role in our evaluation of patients with thoracolumbar burst fracture, and there are several variables available for kyphotic deformity assessment, including Cobb angle, Gardner angle, and sagittal index. However, it remains unknown about intra- and inter-observer variability of sagittal index. Aim The purpose of this study is to determine the reliability of the measurement for thoracolumbar burst fracture kyphosis using Cobb angle, Gardner angle, and sagittal index. Thirty-five patients with thorocolumbar burst fractures treated in our institute were identified. The lateral spine radiographs and midsagittal CT images of the 35 patients were measured on two separate occasions, in random order, by five attending spine surgeons using Cobb angle, Gardner angle, and sagittal index. Method We statistically assessed the agreement, the intra-observer and the inter-observer reliability of the three methods. The intra-observer reliability is always better than the inter-observer reliability, regardless of the parameter being measured or the imaging modality. Results Intra-class correlation coefficients (ICC) were the most consistent for Cobb angle, followed by Gardner angle and sagittal index. Midsagittal CT images had better intra- and inter-observer reliabilities than lateral plain radiography. Also, agreement was better using midsagittal CT images as compared with lateral plain radiography. Conclusion The results of our study suggest that Cobb angle is the most consistent in terms of intra- and inter-observer reliabilities in the assessment of thoracolumbar burst fracture kyphosis.