Standard orientation of the pelvis: validation on a model and ten patients.
OBJECTIVE
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.


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 degrees in the model study and better than 1.5 degrees in the patient study. Accuracy, expressed as angle between ideal and measured coordinate axes, was 0.1 degrees 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.


CONCLUSIONS
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.
Olivecrona
L
L
Department of Radiology, Karolinska University Hospital Solna, Stockholm, Sweden. charlotta.olivecrona@karolinska.se
Aspelin
P
P
Weidenhielm
L
L
Stark
A
A
Noz
M E
ME
Maguire
G Q
GQ
Zeleznik
M P
MP
Svensson
L
L
Olivecrona
H
H
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D010384:Pelvic Bones / Q000000981:diagnostic imaging*; D011187:Posture; D015203:Reproducibility of Results; D036542:Tomography, Spiral Computed