Biomechanical comparison of hard and soft hip protectors, and the influence of soft tissue

Introduction: Hip protectors appear to be promising in preventing hip fractures. Currently, many different hip protectors exist, and it is not clear which hip protector has the best biomechanical properties. Therefore, the objective of this study was to compare the force attenuation capacity of 10 different hip protectors. Both hard hip protectors, which primarily shunt away energy, and soft hip protectors, which primarily absorb energy, were included. Methods: Using a drop weight impact testing system and a surrogate femur, a weight of 25 kg was dropped from a height of 8 cm causing a force of almost 7806 N on the bare femur, which simulates a severe fall. After this calibration test, soft tissue and the different hip protectors in combination with the soft tissue were tested. Each test was repeated six times. To simulate normal-weight elderly people, a 1/2-inch-thick layer of foam was chosen, reducing the force by 18%. To examine the influence of soft tissue thickness, soft tissue was also simulated by a 1-inch-thick layer of foam, reducing the force by 49%. Results: In the 1-inch soft tissue test, all hip protectors were capable in reducing the impact to below the average fracture threshold of elderly people (3100 N), although the hard types performed significantly better than the soft ones (P < 0.001). In the 1/2-inch soft tissue test, only the hard hip protectors were capable of attenuating the peak force to below the average fracture threshold of 3100 N (hard vs. soft hip protectors: P < 0.001). Conclusions: This study showed that the hard, energy-shunting hip protectors were superior to the soft, energy-absorbing ones, especially in a simulation of normal-weight elderly people. With increased soft tissue thickness, soft hip protectors were also capable in reducing the impact to below the average fracture threshold of 3100 N.