The effect of pelvic tilt on radiographic markers of acetabular coverage

Radiographic indices of acetabular coverage are crucial to objectively characterize femoroacetabular impingement and plan bony decompression. It is established that changes in pelvic inclination result in alterations of acetabular crossover; however, it is unclear what influence this has on other measures of acetabular anatomy.

The objective of the present study was to determine if, and to what degree, a variation in pelvic tilt alters 4 measures of acetabular anatomy: the angle of Sharp, Tönnis angle, percentage of acetabular crossover, and lateral center edge angle (LCEA). The hypothesis was that pelvic tilt would significantly alter all measures of acetabular coverage.

Descriptive laboratory study.

Fluoroscopic images of 8 adult hemipelvises were obtained at 7 positions of rotation in the sagittal plane to investigate the change of each measurement in response to pelvic orientation. Two reviewers obtained measurements from each image at 2 separate time points.

Each increment of pelvic inclination resulted in increased measures of acetabular coverage for all measurements, whereas each increment of decreased pelvic inclination resulted in decreased measures of acetabular coverage for all measurements. Significant differences in the measured LCEA, acetabular crossover, and Tönnis angle were identified at each increment of tilt as compared with neutral radiographs. No significant differences could be identified for the angle of Sharp.

Pelvic tilt significantly alters the measures of LCEA, crossover, and Tönnis angle in this cadaveric study. Pelvic inclination results in increased measures of acetabular coverage, whereas decreasing inclination decreases each measure.

Given the known individual and positional pelvic tilt variability, standing anteroposterior pelvic radiographs may provide a more physiological representation of acetabular coverage in the young adult population.