Energy-shunting external hip protector attenuates the peak femoral impact force below the theoretical fracture threshold: An in vitro biomechanical study under falling conditions of thel elderly

Abstract

The first objective of this study was to design a hip protector that would effectively attenuate and shunt away from the greater trochanter the impact energies created in typical falls of the elderly. As the shock absorption material, the protector included the 12 mm-thick Plastazote, which was found to be the most efficient energy-absorbing material in our previous in vitro biomechanical tests. With an anatomically designed semiflexible outer shield of the protector (high density polyethylene), the impact surface was increased and the impact energy shunted away from the greater trochanter. In the second phase of the study, we determined the force attenuation capacity of this device in realistic (in vitro) falling conditions of the elderly. With the impact force of 6940 N used (a typical hip impact force measured in in vitro falling tests), the trochanteric soft tissue (25 mm-thick polyethylene foam) attenuated the peak femoral impact force to 5590 N and the tested protector to 1040 N. In the second series of this experiment, the peak femoral impact force was set to be so high (13,130 N) that the protector, if effective, should prevent the hip fracture in almost all cases. The trochanteric soft tissue attenuated this peak impact force to 10,400 N and the tested protector to 1810 N. Thus, the force received by the proximal femur still remained clearly below 4170 N, the average force required to fracture in vitro the proximal femur of the elderly in a fall loading configuration. In conclusion, our test results suggest that an anatomically designed energy-shunting and energy-absorbing hip protector can provide an effective impact force attenuation in typical falling conditions of the elderly. However, the efficacy of the protector in the prevention of hip fractures can only be evaluated in randomized clinical trials.

Hip protectors: recommendations for biomechanical testing—an international consensus statement (part I)

“…Hip protectors have traditionally incorporated plastic shells for enhanced energy shunting and force distribution [17, 18]. However, recent attention has shifted to soft shell (foam) protectors which lack a rigid shell and may provide better comfort and adherence [19–21].…”

The effect of positioning on the biomechanical performance of soft shell hip protectors

“…Previous biomechanical studies have reported that, when tested in mechanical systems that simulate a fall on the hip, hip protectors attenuate the peak force at the femoral neck by between 17% and 89%, and in some cases, reduce it to a value below the average fracture threshold (310071200 N) of elderly women (Laing and Robinovitch, 2008;van Schoor et al, 2006;Kannus et al, 1999;Parkkari et al, 1995). However, it remains unclear how hip protectors redistribute pressure over the hip region biomechanically.…”

Fractures in the elderly: when is hip replacement a necessity?

“…These devices consist of a contoured plastic or foam shield which can be worn in specially designed pockets in the underwear. The pad is designed to absorb or dissipate energy and is placed over the greater trochanter 11,12. Conflicting reports exist on the efficacy of hip protector pads in reducing the incidence of hip fractures 13–15.…”