Prediction of impact force in sideways fall by image-based subject-specific dynamics model

Abstract

The impact force applied to the greater trochanter during sideways fall is a critical factor for determining whether or not a hip fracture would occur. However, the impact force is subject-dependent as it is related to the subject's anthropometric parameters and the kinematic variables in fall. It cannot be accurately predicted by the currently available dynamics models. We developed and validated a method for constructing subject-specific dynamics models to more accurately predict the impact force. The anthropometric parameters required in the model were obtained from the subject's whole body DXA (dual energy X-ray absorptiometry) image. The subject-specific dynamics models were then validated by protected fall tests using young volunteers. The effects of anthropometric parameters on the impact force were investigated using 90 clinical DXA images obtained from a local osteoporosis clinic center. The impact forces predicted by subject-specific dynamics models had much better agreement with the experimental data, compared with those predicted by the existing empirical functions. The parametric study results indicated that although body weight and height are the dominant parameters affecting the impact force, other parameters such as the hip vertical velocity before impact also have considerable effects. This finding suggests that the existing empirical functions that only consider body weight and height may not be able to accurately predict the impact force. As whole body DXA images are readily available in osteoporosis clinic centers, the proposed method may have potential applications in the clinic to improve the assessment of fallinduced hip fracture risk.

A biomechanical sorting of clinical risk factors affecting osteoporotic hip fracture

“…However, other parameters also have effects on the impact force, for example, the soft tissue over the hip is able to attenuate the impact energy during sideways fall [109,113]; even the body configuration just Fig. 1 Load-strength ratio, major and sublevel biomechanical variables before touching the ground may change the magnitude of impact force [8,112,116]. A more accurate way is to determine the impact force by fall simulation using a dynamics model constructed from the subject's whole body medical image [8,111,113,114].…”

“…1 Load-strength ratio, major and sublevel biomechanical variables before touching the ground may change the magnitude of impact force [8,112,116]. A more accurate way is to determine the impact force by fall simulation using a dynamics model constructed from the subject's whole body medical image [8,111,113,114]. It should be realized that assumptions, for example, the fall type and direction, have been introduced in both fall tests and dynamics simulations, which may be very different from those in a real-world fall.…”

“…Therefore, risk prediction is more challenging than risk assessment. In risk assessment, reasonable assumptions can be introduced to simplify fall dynamics, for example, it can be assumed that the fall is a sideways fall from a standing height with specified floor/ground conditions [8]. In risk prediction, the real impact force is very difficult if it is not impossible to determine, as the impact force depends on a number of subject-specific anthropometric parameters and situationdependent environmental conditions, as well as uncertainties in the variables.…”

“…For assessment purpose, the impact force can be estimated from fall test [14, 17, [106][107][108][109][110] or determined by fall dynamics simulation [8,[111][112][113][114]. Empirical formulas established from experimental data have been proposed to estimate the impact force using the subject's body weight and height [107,110,115].…”

“…Other risk factors that may have substantial contribution to osteoporotic fracture have not been considered, for example, accident fall and the associated impact force [8][9][10][11][12][13][14][15][16][17][18][19][20], geometric parameters of the proximal femur [21][22][23][24][25][26][27][28][29][30][31][32], other chronic medications [33][34][35][36][37] and dietary habits [38][39][40][41][42][43], and lifestyle [44] and health status [45,46]. Even economic status may influence bone density [47].…”