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

Abstract

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.

Keywords: Grayscale inversion view; Spinopelvic parameters; Standard view.

Fig. 1

Methods of measurements of spinopelvic parameters on the standard view (a, c) and the grayscale inversion view (b, d). Thoracic kyphosis was defined as the value of angle between the upper endplate of the T5 and the lower endplate of T12. Lumbar lordosis was defined as the value of angle between the superior endplate of L1 and the superior endplate of S1. Sagittal vertical axis was defined as the horizontal distance between the postero-superior corner of the sacrum and the C7 plumb line. Pelvic incidence was defined as the value of the angle between the line perpendicular to the superior plate of S1 at its midpoint and the line connecting this point to the center of the line connecting the centers of the femoral heads. Sacral slope was defined as the value of the angle between the superior plate of S1 and a horizontal line. Pelvic tilt was defined as the value of the angle between the vertical and the line connecting the midpoint of the sacral plate to the axis of the femoral heads

Fig. 2

An illustration of the spine showing the lines and angles

Fig. 3

An illustrative figure demonstrating the profiles of two femoral heads and the postero-superior corner of the sacrum on the standard view (a) and the grayscale inversion view (b). Compared with the standard view, the profiles of femoral heads and the postero-superior corner of the sacrum look much distinct on the grayscale inversion view