Does Pelvic Rotation Alter Radiologic Measurement of Anterior and Lateral Acetabular Coverage?

The purpose of this study was to determine the radiologic tolerance of the lateral center edge angle (LCEA) and anterior center edge angle (ACEA) to pelvic rotation.

Eleven dry cadaveric pelvises from an osteological collection were reconstructed and placed in anatomic position with corresponding bilateral proximal femurs. Conventional anteroposterior (AP) and false-profile (FP) pelvic radiographs were taken at 5° increments with fluoroscopy from 0° to 25° of rotation. LCEA and ACEA were measured for conventional and rotated AP and FP fluoroscopic views, respectively. Statistical analysis was conducted to determine the error in ACEA and LCEA with pelvic rotation.

The mean LCEA was 29.1° (95% confidence interval [CI], 25.5°-32.7°). Mean ACEA was 38.9° (95% CI, 34.1°-43.8°). There was significant change in the LCEA past 10° of rotation (P = .041). There was significant change in the ACEA with 5^o or more of rotation (P < .001). The FP view rotated 40° from an AP view produced 6.8° (95% CI, 4.7-8.9) of error, whereas one rotated 90° from an AP view produced 13.2° (95% CI, 11.2°-15.3°) of error in the ACEA. An AP view rotated 25° toward the x-ray beam produced 2.3° (95% CI, 1.1°-3.4°) error, whereas one rotated 25° away from the beam produced 2.6° (95% CI, 1.5°-3.8°) of error.

Rotation of AP and FP radiographs significantly affects the measured values of the LCEA and ACEA, respectively. The ACEA experiences more dramatic changes with rotation of the FP view compared with the LCEA with the same amount of rotation of an AP view. This study illustrates the importance of verifying the quality of the FP radiograph when using ACEA to guide therapy for hip pathology.

This study emphasizes the importance of evaluating pelvic rotation when using the center edge angle to assess femoral head coverage.