Validation study of the CT-based cross-sectional evaluation of muscular atrophy and fatty degeneration around the pelvis and the femur.

BACKGROUND Muscle atrophy and degeneration around hip joint have been evaluated using computer tomography (CT) or magnetic resonance imaging two-dimensionally (2D). However, it is unclear how these 2D measurements of muscle atrophy and degeneration reflect their three-dimensional (3D) measurements. The purpose of this study is to examine the validity of the 2D evaluation of muscular atrophy and fatty degeneration compared to 3D evaluation. METHODS The study included computed tomography (CT) images of 20 patients with unilateral hip joint disorders. We manually segmented the edges of 14 muscles around the pelvis and the femur. The correlation coefficient between the 3D and 2D measurements at the anatomic landmarks was calculated. Furthermore, the 2D evaluation was performed at 1 cm interval from each anatomic landmark to determine the cross-section that correlated most strongly with the 3D measurements. A strong correlation in Spearman's rank correlation coefficient (r) was defined as r > 0.7. RESULTS Nine (64%) and 10 (71%) muscles had a strong correlation coefficient between the 3D and 2D anatomic landmark measurements of muscular atrophy and degeneration, respectively. The maximum distance between the cross-section with the highest correlation coefficient and the anatomical landmark was 11 cm. CONCLUSIONS More than half of muscles exhibited a strong correlation between the 3D and 2D anatomic landmark measurements of muscular atrophy and degeneration. To improve the correlation coefficient, the position of the cross-section was needed to be changed.