Age-related decrease in supratrochanteric torsion and increase in infratrochanteric torsion in healthy pediatric femurs: an MRI study.

The aim of the study was to evaluate the correlation between femoral anteversion, supratrochanteric torsion (STT), and infratrochanteric torsion (ITT) in healthy developing pediatric femurs using MRI. This study included 282 (164 males and 118 females) patients aged 1-18 years. The axial MRI of patients with benign tumoral lesions of the femur was retrospectively reviewed. The measurements were performed through axial images of contralateral healthy femurs. Femoral anteversion, STT, and ITT were measured twice by two orthopedic surgeons. The Pearson correlation coefficient was used to test for the correlation of age between STT, ITT, and femoral anteversion in children. All femoral anteversion, STT, and ITT measurements showed excellent intraobserver and interobserver reliability (P < 0.001). The mean STT changed from 68.5° to 37.2°  ±  4.2, the mean ITT changed from -37.4° to -21.2°  ±  4.2, and the mean femoral anteversion changed from 31.1° to 18.8°  ±  2.2 in patients aged 1-18 years. Through the linear regression model, STT, ITT, and femoral anteversion had a significant association (P < 0.001) with age. For an increase of one year in age, the corresponding STT decreased 1.32 times (P < 0.001, R2 = 0.510), the corresponding ITT increased 0.39 times (P < 0.001, R2 = 0.079), and the corresponding femoral anteversion decreased 0.94 times (P < 0.001, R2 = 0.507). ITT increases and STT decreases with age. The decrease in STT contributes more to femoral anteversion than does the increase in ITT. STT and ITT contribute to femoral anteversion with different patterns according to age.