Grayscale inversion radiographic view provided improved intra- and inter-observer reliabilities in measuring spinopelvic parameters in asymptomatic adult population

BACKGROUND: Recently, a grayscale inversion view was reported to improve intra- and inter-observer reliabilities in measuring coronal curvature with Cobb and pedicle methods in scoliosis patients. However, the grayscale transformation has never been applied to the measurements of spinopelvic parameters. The purpose of this study was to compare the measurement reliabilities of the spinoplevic sagittal parameters between the ‘Standard View’ and the ‘Grayscale Inversion View’ in normal adult populations. METHODS: A total of 30 asymptomatic subjects aged between 30 and 40 years were included in this study. Whole-spine posteroanterior radiographs were used to measure the spinoplevic sagittal parameters including thoracic kyphosis (TK), lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic incidence (PI), sacral slope (SS) and pelvic tilt (PT) in both standard view and grayscale inversion view. Two independent observers measured the parameters twice at a 2-week interval. Intra- and inter-observer reliabilities were compared between the two radiographic views. The absolute differences between the two sets of measurements on each view were calculated and compared. RESULTS: The intra-class correlation coefficients (ICCs) of PI, PT and SVA were greater in the grayscale inversion view than in the standard view (0.972 vs 0.817, 0.937 vs 0.833 and 0.964 vs 0.901 for observer 1, respectively; 0.990 vs 0.826, 0.995 vs 0.842 and 0.969 vs 0.919 for observer 2, respectively). Overall, the improvement of ICC was greater in parameters of sagittal pelvic alignment than in those of sagittal spinal alignment. As for the mean absolute differences between two measurements, significant differences existed between the two views in terms of PI, PT and SVA (p = 0.014, 0.016 and 0.011 for observer 1, respectively; p = 0.014, 0.025 and 0.046 for observer 2, respectively). CONCLUSIONS: A grayscale inversion view provided improved intra- and inter-observer reliabilities in measuring spinoplevic alignment when compared with a standard view. This view was more useful in subjects whose pelvic anatomical structures can’t be identified clearly on the standard X-ray view.