Femoral anteversion in the hip: comparison of measurement by computed tomography, magnetic resonance imaging, and physical examination.

Purpose: The purpose of this study was to evaluate the correlation between computed tomography (CT) and magnetic resonance imaging (MRI) measurements of femoral anteversion, as well as the relation of anteversion with physical examination and radiographic findings.
Methods: Preoperative CT and MRI measurements of anteversion along with clinical examination were performed on 129 consecutive hips before hip arthroscopy for nonarthritic hip injuries. All anteversion measurements were performed by 2 musculoskeletal radiologists. The radiographic findings and physical examination findings were analyzed for statistically significant correlations. For statistical analysis purposes, the patients were divided into 3 groups according to the mean CT anteversion measurement: group I (low), less than 10°; group II (medium), 10° to 22°; and group III (high), greater than 22°.
Results: High interobserver correlation was found for femoral anteversion measurement by CT and MRI (r = 0.95 and r = 0.86, respectively; P < .0001 for both). CT and MRI measurements showed high correlation with each other (r = 0.80, P < .0001). However, in 96% of the cases, the CT measurement was larger, with a mean difference of 8.9° (range, -37° to 1.5°). A significant correlation coefficient was found between internal rotation and anteversion angles as measured by CT (r = 0.36, P < .0001). However, no correlation was found with other hip movement measurements. Abnormal femoral acetabular bony architecture of the hip was found in 64% of the patients; isolated cam impingement was more prevalent in group I, whereas isolated pincer impingement was more prevalent in group III (P = .01).
Conclusions: Although high correlation was found between anteversion angle measurements by CT and MRI, significant discrepancies in the absolute anteversion number between the 2 techniques suggest that they may not be interchangeable. Furthermore, CT was found to have higher interobserver reliability than MRI. There was a significant correlation between CT and examination of internal rotation of the hip. Clinically, the findings of the study show that the diagnosis of excessive femoral anteversion or retroversion should have different thresholds according to MRI and CT measurements; moreover, the diagnosis should not rely exclusively on either examination or radiologic criteria.
Level of Evidence: Level III, retrospective comparative study.
(Copyright © 2012 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)