Purpose: To validate an image post‐processing method for re‐orienting the pelvis in CT volumes to a standardized orientation in a model and in 10 patients.
Material and Methods: Twenty‐four CT volumes of a pelvic model and 10 pairs of postoperative total hip arthroplasty (THA) patient CT scans were rotated to a defined pelvic standard orientation and the rotation was recorded. For precision, a test‐retest procedure was used. For accuracy, three exactly represented coordinate points were used. For clinical application, the standard orientation was used for calculating the direction of acetabular cup migration from a previous model study.
Results: Precision of pelvic standard orientation, calculated as maximal directional error, was better than 1° in the model study and better than 1.5° in the patient study. Accuracy, expressed as angle between ideal and measured coordinate axes, was 0.1° for x, y, z axes. No measurable systematic errors were found. When applied to acetabular cup migration in the model, standardization of pelvic orientation had no significant effect on the measurements.
Conclusion: Reorienting the pelvis during image post‐processing was shown to be accurate. It enables measurements relative to the pelvis and minimizes the dependency of patient positioning.
