2017 ISAKOS Biennial Congress ePoster #501

 

Does Pelvic Rotation Alter Radiographic Measurements of Acetabular Coverage?

Ryan T. Li, MD, Pittsburgh, PA UNITED STATES
Heath Patrick Gould, MD, Baltimore, Maryland UNITED STATES
Emily Hu, BA, Cleveland, OH UNITED STATES
Raymond W Liu, MD
Michael J. Salata, MD

University Hospitals Case Medical Center, Cleveland, UNITED STATES

FDA Status Not Applicable

Summary

Pelvic rotation affects the both the lateral center edge angle and anterior center edge angle

Abstract

Introduction

Over-coverage and under-coverage of the femoral head by the acetabulum are both important factors in hip pathology. The lateral center edge angle (LCEA) measured on an AP pelvic radiograph and anterior center edge angle (ACEA) measured on a false profile radiograph are commonly used to assess acetabular coverage of the femoral head. While it is well known that certain hip parameters are susceptible to pelvic rotation, the LCEA and ACEA susceptibility to pelvic rotation have not been well determine. The objective of this study was to determine the tolerance of the LCEA and ACEA to pelvic rotation.

Methods

10 dry cadaveric pelves from the Hamann-Todd osteological collection were randomly selected, reconstructed and placed in anatomic position with corresponding proximal femurs. Conventional AP and false profile pelvic radiographs were taken with a fluoroscopic C-arm with 0 to 25° of rotation. LCEA and ACEA were measured by two individuals at each position for conventional and rotated AP and false profile radiographs, respectively. Statistical analysis was conducted to determine the error in ACEA and LCEA with pelvic rotation. Intraclass correlation coefficient was calculated to determine inter-rater and intra-rater reliability of measurements.

Results

The mean LCEA was 29.1° (95% CI 29.7°-36.9°). Mean ACEA was 38.9° (95% CI 34.1°-43.8°). ICC was 0.76 for inter-rater reliability and 0.84 for intra-rater reliability. There was significant change in the LCEA and ACEA with pelvic rotation at every position from 5 to 25 degrees. Over-rotation and under-rotation of an AP radiograph by 25 degrees produced 2.54 (95% CI 0.38-4.69) and 3.56 (95% CI 1.49-5.64) degrees of error in the LCEA respectively. Over-rotation and under-rotation of a false profile radiograph by 25 degrees produced 5.68 (95% CI 2.04-9.32) and 14.53 (95% CI 10.56-18.50) degrees of error in the ACEA respectively.

Conclusions

Rotation of an AP radiograph and false profile radiograph significantly alters measurement of both the LCEA and ACEA. However, the ACEA is significantly more susceptible to pelvic rotation of a false profile radiograph compared to the the LCEA and similar rotation of an AP radiograph. This study illustrates the importance of verifying the quality of a false profile radiograph when using ACEA to guide therapy for hip pathology.