CLINICAL RESEARCH Pelvic Rotation and Tilt Can Cause Misinterpretation of the Acetabular Index Measured on Radiographs

Background Radiographic diagnosis and followup studies of developmental dysplasia of the hip are commonly performed by measuring the acetabular index on radiographs using Hilgenreiner’s method. The outcome of the measurement, however, depends on the orientation of the subject’s pelvis relative to the xray source. The influence of pelvic rotation and tilt on the measurement error has been evaluated separately but not in combination. Questions/purposes We asked whether (1) combinations of pelvic rotation and tilt introduced systematic error in acetabular index measurement in a reproducible way, and (2) ratios proposed to evaluate either pelvic rotation (Rrotation) or pelvic tilt (Rtilt) are influenced by pelvic tilt and rotation, respectively. Methods Radiographic measurements of the acetabular index, Rrotation, and Rtilt were performed on digitally reconstructed radiographs of one high-resolution Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. Each author certifies that his or her institution approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.