Biomechanical testing of hip protectors and energy-absorbing floors for the prevention of fall-related hip fractures

The general objective of my thesis research was to characterize the stiffness and force distribution characteristics of the hip region during the impact phase of sideways falls, and to advance our understanding of the potential for external engineering interventions (e.g. hip protectors and compliant floors) to reduce hip fracture risk by reducing the force applied to the proximal femur during such falls. This thesis is comprised of five studies. In the first I characterized the degree of non-linearity in pelvic stiffness, and examined the influence of stiffness characterization methods on the accuracy of mathematical models (mass-spring and Voigt) in predicting impact dynamics during falls on the hip. In the second study I employed a pelvis release paradigm (a method of inducing low severity but clinically relevant falls) to examine whether soft shell hip protectors alter the distribution of force throughout the hip region during impact. The third study entailed a sensitivity analysis to determine the influence of mechanical test system properties on the force attenuation provided by hip protectors. In the fourth study I used pelvis release experiments to determine how the force applied to the pelvis is affected by body impact configuration and floor stiffness; I also examined the ability of a mass-spring model to predict these relationships. The final study used a mechanical fall simulator to assess the attenuation in femoral neck force provided by four low stiffness floors compared to a standard rigid floor, and assessed the influence of these floors on fall risk through a range of static and dynamic balance tests with fifteen elderly women. Overall, this thesis demonstrates that compliant floors and soft shell hip protectors substantially reduce the force applied to the proximal femur during the impact stage of sideways falls. Of equal importance, this work demonstrates the need for international standards for the biomechanical testing and market approval of these devices. These are essential steps for increasing the quality of hip protectors and compliant floors available in the marketplace, and consequently, for enhancing their ability to reduce hip fracture risk in vulnerable populations.