Influence of Physical Activity in Morphologic Variation of Proximal Femur Among Prepubertal Boys

Research analyzing the influence of physical activity (PA) on skeletal have been focused on bone material properties such as bone mass and few studies were conducted on bone morphologic properties.

Purpose To analyze the influence of PA on morphologic variation of proximal femur in pre-pubertal boys, probably the most active group in non athletic population. Methods: Participants were 68 boys (age: 8.6±0.4 yrs; bone age: 8.9±1.1 yrs; height: 1.33±0.06 m; BMI: 18.0±2.9 Kg/m²). Analysis of the proximal femur was performed in DXA 2D images with a morphometric approach using 18 anatomical and Type III landmarks in order to quantify shape differences among participants. PA was assessed with the Actigraph accelerometer (model WAM 7164) over seven days. The outcome variable was the number of minutes per day the child engaged in moderate and vigorous PA. A cut point of 1952 counts/min was used to represent moderate and vigorous PA.

Results Exploratory relative warp (RW) analysis performed with TPDRelw 1.45 (Rohlf 2007), showed that the first RW (RW1) represented the major axis of shape variation, which explained 65.5% (SV=0.72627) of the total variance of proximal femur. This deformation along the RW1 axis was mainly described by differences in relative positioning of Ward’s area. Two main specimen clusters were founded one in the negative extreme of RW1 and the other on the opposite part. Consequently a more detailed description on RW1 and its observed shape differences was conducted. In the negative extreme of the RW1 it was observed that Ward’s area was located at the middle of the upper limit of femoral neck width. In the positive extreme of the RW1, Ward’s area was positioned on the neck axis under the lower limit of femoral neck length. Regression analysis using shape variables as dependent and moderate plus vigorous PA as independent variable demonstrated that PA accounted for 4% of the variance explained (F=3.3841, df=32; p<0.01).

Conclusion Proximal femur morphologic variation in pre-pubertal boys seemed to be mainly due to differences in the position of Ward’s area, the region of femoral neck with the lowest bone mineral density. Although statistically significant, PA only accounted for 4% of all shape variation of proximal femur.