Distal femoral aspect ratios throughout childhood: an MRI study of normative data and sex comparisons.

Abstract

The ratio of anteroposterior (AP) to medial-lateral (ML) dimensions of the distal femur in adults differs by sex. The average AP/ML dimension ratios are 0.82 for females and 0.79 for males. How and when this difference develops is not yet understood. In this study, the distal femoral dimensions and physeal development of 345 participants younger than 21 years of age were evaluated by MRI. Regression analysis indicated a significant increase in the AP/ML ratio with increasing age for both sexes. In girls, the ratio increased from 0.63 at ages 0-5 years to 0.76 at 15-20 years. In boys, the ratio increased from 0.61 to 0.73 over the same age groups. Female distal femur dimensions are narrower than that of males from birth. Throughout childhood, both sexes show gradual increases in AP/ML ratios. After closure of the physes, the AP/ML ratio in children approaches adult values, with females continuing to have relatively narrower dimensions than males.