Wearable Hip Protectors: Validation of a Novel Test System and Evaluation Utilizing Pressure Sensing Methods
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Hip fractures are strongly associated with sideway falls to the hip, poor response time, lack of soft tissue energy absorption, and subpar proximal femur strength (Cummings and Nevitt, 2001). Hip protectors are a common intervention aimed to lower the femoral neck loads below the fracture threshold and reduce the risk of hip fracture (Robinovitch et al., 2009). These protective devices typically consist of a padded material embedded in undergarments which absorb or shunt impact energies. Lack of testing standards for these protective devices have resulted in many unregulated hip protectors produced, a wide range of biomechanical test results represented by various test systems, and inconclusive clinical trials (Combes and Price, 2014; Kannus et al., 1999; Laing et al., 2011; van Schoor et al., 2006). The International Hip Protector Research Group (IHPRG) have consolidated evidence-based recommendations for the specifications and parameters for a biomechanical hip protector test system (Robinovitch et al., 2009). A drop tower and surrogate pelvis test system was developed to evaluate various hip protectors in a simulated sideways fall from a range of impact velocities. This test system was validated using the IHPRG recommendations and compared with femoral neck loads for unpadded and padded conditions in Laing et al. (2011). After testing combinations from 3 different foam products and 2 different trochanteric soft tissue thicknesses (TSTT), the selected baseline hip form consisted of a FlexFoam-iT! V product at a 24 mm TSTT. When tested at a 3.4 m/s impact velocity, this baseline hip form had an average peak femoral neck force of 2145 N and an average peak neck force attenuation of 20.1% and 25.9% for Hipsaver and Safehip Air-X protectors respectively, which closely matched the test system used in Laing et al. (2011). The test system with this baseline hip form was then verified to have excellent reliability between trials (ICC = 0.99 average across impact velocities) and poor reliability between hip forms (ICC range = -0.18 to 0.404 between impact velocities). Additionally, the hip form did not incur any visible interior or exterior damage after being drop tested for 60 repeated impacts at the specified various velocities. Only a few studies had previously looked into pressure distribution of hip protectors during simulated falls. Limitations in literature include the evaluation of pressure only at the outer surface of the hip protector and at low impact velocities. The Tekscan I-Scan pressure mapping system allowed for measurements directly at the hip protector-skin interface for impact velocities up to 3.4 m/s. The goal of this study was to look at significant differences between hip protector conditions for various force and pressure-related outcome variables, investigate which pressure-related variables were related to the traditional biomechanical effectiveness metric, and to provide initial insight regarding the protective mechanism of hip protector designs. Significant differences between the unpadded and the four hip protectors were seen except for total force at 3.4 m/s. Significant associations were observed between peak neck force attenuation and average pressure at 2.8 m/s and contact area at 2.8 m/s and 3.4 m/s. Although peak pressure was independent on peak neck force attenuation, it can be used to distinguish the mechanism of hip protectors where high peak pressure relates to energy-shunting and lower peak pressure relates energy-absorbing. The initial insights show potential for further investigation to use pressure-related variables in hip protector testing and design.
Cite this work
Frederick Goh (2017). Wearable Hip Protectors: Validation of a Novel Test System and Evaluation Utilizing Pressure Sensing Methods. UWSpace. http://hdl.handle.net/10012/12135