Childhood obesity as a risk factor for bone fracture: a mechanistic study

Abstract

Objective: To investigate the risk of bone fracture sustained by obese children exposed to falls. The bone fracture risk of obese children would be greater than that of their nonobese counterparts was hypothesized.

Design and methods: Finite element-based computational models for children that reflected various levels of obesity by varying body mass and the thickness of the subcutaneous adipose tissue layer was developed. The models took account of both the momentum effect of variation of body mass and the cushion effect of variation of soft tissue thickness and examined these two contradictory effects on pelvic bone fracture risk through a set of sideways fall simulations with a range of impact speeds.

Results: The critical impact speed that yielded pelvic bone fracture decreased as the levels of obesity increased, which meant that the momentum effect of a greater body mass took precedence over the cushion effect of the soft tissue layer.

Conclusions: The result suggests that obese children have a greater risk of pelvic bone fracture than do their nonobese counterparts in sideways falls. A further implication is that current child safety devices, systems, and regulations will need to be revisited as the prevalence of child obesity increases.

Figure 1

Finite Element (FE) Model of the Pelvis-Femur Complex Including Skin, Subcutaneous Adipose Tissue (SAT), and Homogeneous Soft Tissue (HST). The points in the top row are the measuring points used to calculate pelvic compression and viscous criteria. (a) Pelvis bone surface extracting. (b) Normal model, TST=3.6 mm. (c) TST=8.6 mm. (d) TST=16.3 mm. (e) TST=24.7 mm. TST indicates nominal trochanteric SAT thickness.

Figure 2

Model Validation. The bold line indicates the simulation. All curves other than the bold line are from the experimental data by Ouyang et al. (24). (a) Impact force versus pelvic deformation. (b) Viscous criteria versus time.

Figure 3

Results of Sideways Fall Simulation Using the Pelvis-Femur Complex. (a) Impact force. (b) Viscous criteria. (c) Strain energy absorbed by subcutaneous adipose tissue (SAT) and skin. (d) A snapshot for sideways fall simulation and bone fracture. Color contour indicates von-Mises stress. (e) Comparison of critical impact speeds that yield bone fracture (mean values and ± standard deviations of the test results with the use of four different floor properties). TST indicates nominal trochanteric SAT thickness.

Figure 4

Results of Sideways Fall Simulation Using the Full-Body Model. (a) Impact force. (b) Viscous criteria. (c) Strain energy absorbed by subcutaneous adipose tissue (SAT) and skin. (d) A snapshot for sideways fall simulation and bone fracture. Color contour indicates von-Mises stress. (e) Comparison of critical impact speeds that yield bone fracture (mean values and ± standard deviations of the test results with the use of four different floor properties).