Validation of postural radiographs as a way to measure change in pelvic obliquity

OBJECTIVE: To evaluate the validity of using postural radiographs to assess change in pelvic obliquity. DESIGN: Blinded comparison of reference lines and instrument development of postural radiographs. SETTING: Veterans Administration hospital. PARTICIPANTS: Thirty-nine subjects with no history of low back pain. INTERVENTION: Repeated postural radiographs without heel lifts and with (1/4)-in (6.35-mm) and (1/2)-in (12.7-mm) heel lifts. MAIN OUTCOME MEASURE: The change of pelvic obliquity as measured by the intersulcate, interalar, and sacral surface lines on postural radiographs. RESULTS: A (1/4)-in heel lift resulted in changes of 4.6+/-4.0mm, 3.6+/-3.1mm, and 5.8+/-3.9mm and a (1/2)-in heel lift in changes of 7.8+/-4.3mm, 7.8+/-4.6mm, and 5.2+/-3.8mm for the intersulcate, interalar, and sacral surface lines, respectively. Pearson correlation coefficients were used to correlate the change in pelvic obliquity with the corresponding heights of heel lifts; for the (1/4)-in heel lift, they were.67,.88, and.71, and for (1/2)-in heel lift they were.73,.79, and.87 for the intersulcate, interalar, and sacral surface lines, respectively (all P<.001). CONCLUSION: All the reference lines seem to be valid measures of change of pelvic obliquity relative to the size of the lifts (ie, the changes in pelvic obliquity seem to be causally related and correlated with the lifts). These results also suggest that postural radiographs can be used to determine the magnitude of pelvic obliquity.