CT and MRI lower extremity torsional profile studies: measurement reproducibility

Assessment of lower extremity (LE) torsional profile using computed tomography (CT) imaging is a well-recognized imaging method that supplements the clinical examination. Magnetic resonance imaging (MRI) is another advanced imaging modality that can be used as an alternative, since there are many growing concerns of radiation exposure with traditional CT studies, particularly in the skeletally immature population.

Sixty-two patients between the ages of 7 and 19 years were included. Thirty-four had CT and 28 had MRI for assessment of LE torsional profile. All patients had clinical evidence of torsional malalignment. CT and MR images were randomized and de-identified. Two observers measured femoral anteversion and tibial torsion based on previously published methodologies. This exercise was repeated 2 weeks later and the data were tabulated and statistical analysis was performed. Radiation exposure for the patients studied by CT was estimated.

The mean age of the patients was 14.4 years (range 9.5-18.9 years) and 13.8 years (range 7.3-18.9 years) for the CT and MRI groups, respectively. Inter-observer reliability for both CT and MRI studies were excellent. The intra-class correlation coefficient (ICC) for femoral anteversion and tibial torsion studied by CT and MRI for both observers at both times were excellent. The radiation exposure for CT examination averaged 0.3-0.5 mSv, compared to none with the MRI method.

MRI provides a reproducible method for assessing the torsional profile in children and adolescents using similar anatomic landmarks for measurements as those used on CT torsional profile. In circumstances where MRI methods are readily available (and affordable), the CT torsional profile can be replaced with MRI methods, in the current era of growing concerns of radiation hazards and increasing awareness about radiation safety.

Diagnostic Level III.