Correlation of the cross-over ratio of the cross-over sign on conventional pelvic radiographs with computed tomography retroversion measurements
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To find a correlation between the cross-over ratio of the cross-over sign on conventional anteroposterior (AP) pelvic radiographs and retroversion measurements (‘roof-edge angle’ and ‘equatorial-edge angle) on computed tomography (CT) scans. This would facilitate the interpretation of the cross-over sign regarding the amount of acetabular retroversion.
Materials and methods
Correctly projected AP pelvic radiographs (2,925 hips) were examined for the presence of the cross-over sign (COS), and the overlap ratio of the COS was measured. On CT scans of the same patients the ‘roof-edge angle’ (RE angle) and the ‘equatorial-edge angle’ (EE angle) were also calculated.
A statistically significant but only weak relationship could be found between the overlap ratio of the COS and the ‘roof-edge angle’ (P < 0.0001; correlation coefficient −0.486) and between this ratio and the ‘equatorial-edge angle’ (P < 0.0001; correlation coefficient −0.395).
A relationship between the overlap ratio and orientation measurements on CT scans could be found, but it was less strong than expected.
KeywordsHip Acetabulum Retroversion Impingement Cross-over sign Computed tomography Pelvic radiographs
The authors acknowledge the help given by Prof. Dr. Burkhardt Seifert (Biostatistics Unit, Institute of Social and Preventive Medicine, University of Zurich) with the statistical analysis.
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