Comparison of force attenuation properties of four different hip protectors under simulated falling conditions in the elderly: an in vitro biomechanical study.

The purpose of this in vitro biomechanical study is to determine the force attenuation capacity of four different hip protectors (KPH1, KPH2, Safehip, and Safetypants) in falling simulations in elderly subjects (falls to the side). The simulated falling conditions were created by a biomechanical testing system, which consisted of an impact pendulum, surrogate pelvis and femur, and two load cells. Three series of impact experiments were conducted in an ascending order (low, moderate-, and high-force experiments), each exceeding the literature-provided average (+/- 1 SD) fracture threshold (3100 +/- 1200 N) of the proximal femur of elderly women with a mean age of 71 years. Using a low impact force of 4330 N, the trochanteric soft tissue (20-mm-thick polyethylene foam) attenuated the peak femoral impact force to 3740 N and, accordingly, the KPH1 protector to 590 N, KPH2 to 510 N, Safehip to 1080 N, and Safetypants to 790 N. Thus, in this low force experiment, all tested protectors could reduce the peak impact force entered into the proximal femur below the aforementioned average fracture threshold area (3100 +/-1200 N) of the proximal femur of elderly women. With a moderate impact force of 7230 N, the soft tissue attenuated the peak femoral impact force to 6130 N, and the protectors to 780 N, 760 N, 2240 N, and 2760 N, respectively. Thus, with this impact force, only the KPH hip protectors could reduce the impact force clearly below the fracture threshold area. In the final series of the experiment, the peak femoral impact force was set to be so high (10,840 N) that the protector, if effective, should prevent the hip fracture in almost all cases and situations. The trochanteric soft tissue attenuated this peak impact force to 9190 N, and the tested protectors to 1360 N, 1170 N, 4640 N, and 5770 N. Thus, with the KPH protectors the force received by the proximal femur remained below the average force required to fracture the proximal femur of elderly women, whereas with the two other protectors the impact force entered into the proximal femur clearly exceeded this threshold value. In conclusion, the test results showed that, of the four tested hip protectors, the anatomically designed energy-shunting and energy-absorbing KPH protectors can provide an effective impact force attenuation in a sideways-fall simulation in the elderly, whereas the force attenuation capacity of the two other protectors seems more limited. However, the true efficacy of any protector in the prevention of hip fractures can only be evaluated in randomized clinical trials.