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

Wearable hip protectors represent a promising strategy for reducing risk for hip fracture from a sideways fall. However, small changes in pad positioning may influence their protective benefit. Using a mechanical hip impact simulator, we investigated how three marketed soft shell hip protectors attenuate and redistribute the impact force applied to the hip, and how this depends on displacement from their intended position by 2.5 or 5 cm superiorly, posteriorly, inferiorly or anteriorly. For centrally-placed protectors, peak pressure was reduced 93% below the unpadded value by a 16 mm horseshoe-shaped protector, 93% by a 14 mm horseshoe protector, and 94% by a 16 mm continuous protector. In unpadded trials, 83% of the total force was applied to the skin overlying the proximal femur (danger zone). This was lowered to 19% by the centrally placed 16 mm horseshoe protector, to 34% by the 14 mm horseshoe, and to 40% by the 16 mm continuous protector. Corresponding reductions in peak force delivered to the femoral neck (relative to unpadded) were 45%, 38%, and 20%, respectively. The protective benefit of all three protectors decreased with pad displacement. For example, displacement of protectors by 5 cm anteriorly caused peak femoral neck force to increase 60% above centrally-placed values, and approach unpadded values. These results indicate that soft shell hip protectors provide substantial protective benefits, but decline in performance with small displacements from their intended position. Our findings confirm the need for correct and stable positioning of hip protectors in garment design.