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

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 fall-induced hip fracture risk.