Measurement of Femoral Version by MRI is as Reliable and Reproducible as CT in Children and Adolescents With Hip Disorders.

BACKGROUND: Femoral version measurement techniques based on magnetic resonance imaging (MRI) studies have been developed as an alternative to the high levels of ionizing radiation associated with computed tomography (CT)-based methods. Previous studies have not evaluated the reliability, repeatability, and accuracy of MRI-based femoral version measurements in an adolescent population. METHODS: Subjects who underwent MRI and CT studies for clinical suspicion of hip pain secondary to hip dysplasia or femoroacetabular impingement between 2011 and 2013 were identified. Rapid sequence femoral version images were obtained from MRI Hip dGEMRIC and/or postarthrogram studies. Femoral version images were also obtained from bilateral CT lower extremity, without contrast, studies. Measurements were made by 1 fellowship-trained, pediatric hip preservation attending surgeon, 2 pediatric orthopaedic surgical fellows, and 1 fellowship-trained musculoskeletal radiologist on 2 separate occasions. Linear mixed models were used to estimate the reliability and repeatability associated with CT-based and MRI-based measurements (intraclass correlation coefficients) and to estimate the agreement (CT-MRI) between the 2 techniques. RESULTS: The mean age of 36 subjects was 15.4 years (±4.1 y). Interrater reliability was 0.91 (95% CI, 0.86-0.95) for the CT technique compared with 0.90 (95% CI, 0.86-0.94) for the rapid sequence MRI technique. Intrarater reliability for the CT technique was 0.96 (95% CI, 0.91-0.98) compared with 0.95 (95% CI, 0.90-0.97) for the MRI technique. The agreement between the MRI-based and CT-based techniques (bias: 1.9 degrees, limits of agreement: -11.3 to 14.9 degrees) was similar to the agreement between consecutive MRI measurements (bias: 0.4 degrees, limits of agreement: -7.8 to 8.6 degrees) as well as consecutive CT measurements (bias: 0.5 degrees, limits of agreement: -8.8 to 9.9 degrees). CONCLUSIONS: The interrater and intrarater reliability and repeatability estimates (intraclass correlation coefficient values) associated with both techniques was excellent (>0.90). Acquirement of axial images at the pelvis and knee during MRI for investigation of adolescents with hip pain allows for reliable measurement of femoral version. LEVEL OF EVIDENCE: Level II-diagnostic study.