Force attenuation properties of various trochanteric padding materials under typical falling conditions of the elderly



The purpose of this study was to determine and compare the force attenuation properties of various external trochanteric padding materials under in vitro conditions simulating characteristic falling of the elderly. The selected materials had to be practically suitable for external hip padding so that the main criteria for the materials were good energy absorbing capacity, good durability, low weight, good recovery after compression, easy availability, and reasonable price. Eight materials met these requirements. The first six were flexible cross-linked polyethylene foams with densities from 30 to 200 kg/m3. The seventh material was Plastazote polyethylene foam, and the eighth foam was made of ethylene-vinyl acetate (EVA) copolymer. With a pendulum effective mass of 39 kg, impact velocity of 3.0 m/s, and impact force of 8.2 kN, the force attenuation provided by the 20 mm thick hip-padding materials was quite small, ranging from 22 to 38%. With all these materials the peak femoral force remained above 5 kN, more than two times above the femoral fracture threshold (2 kN). In the second set of experiments, the impact force was gradually reduced until the tested materials lowered the impact force below the fracture threshold. With the most efficient material this critical falling velocity was found to be 1.6 m/s. To go below the fracture threshold with the realistic impact velocity of 3.0 m/s, the padding materials had to be 100-140 mm thick. In conclusion, our test results strongly suggest that using reasonable thicknesses of the currently available hip padding materials, the impact forces clearly remain above the fracture threshold, and therefore, prevention of hip fractures by external protectors should be based on other ideas (increase in the impact surface and/or shunting of impact energy away from the greater trochanter) than hip padding alone.