The Penn State Safety Floor: Part II—Reduction of Fall-Related Peak Impact Forces on the Femur

Abstract

The goal of this study was to develop and validate a finite element model (FEM) for use in the design of a flooring system that would provide a stable walking surface during normal locomotion but would also deform elastically under higher loads, such as those resulting from falls. The new flooring system is designed to reduce the peak force on the femoral neck during a lateral fall onto the hip. The new flooring system is passive in nature and exhibits two distinct stiffnesses. During normal activities, the floor remains essentially rigid. Upon impact, the floor collapses and becomes significantly softer. The flooring system consists of a multitude of columns supporting a continuous walking surface. The columns were designed to remain stiff up to a specific load and, after exceeding this load, to deform elastically. The flooring returns to its original shape after impact. Part I of this study presented finite element and experimental results demonstrating that the floor deflection during normal walking remained less than 2 mm. To facilitate the floor's development further, a nonlinear finite element model simulating the transient-impact response of a human hip against various floor configurations was developed. Nonlinearities included in the finite element models were: changing topology of deformable-body-to-deformable-body contact, snap-through buckling, soft tissue stiffness and damping, and large deformations. Experimental models developed for validating the finite element model included an anthropomorphic hip, an impact delivery mechanism, a data collection system, and four hand-fabricated floor tiles. The finite element model discussed in this study is shown to capture experimentally observed trends in peak femoral neck force reduction as a function of flooring design parameters. This study also indicates that a floor can be designed that deflects minimally during walking and reduces the peak force on the femoral neck during a fall-related impact by 15.2 percent.

Effect of compliant flooring on impact force during falls on the hip

“…Our results are in general agreement with previous studies that employed mechanical systems to estimate the effect of compliant flooring on fall impact force, 10,11 although the comparison is made difficult by the fact that previous studies did not report the stiffness of their floor samples. The 8% attenuation we observed in the firm condition is similar to the 7% reduction observed by Gardner et al 11 for a pile carpet and underpad and the 11% reduction observed by Maki and Fernie 12 for 7 mmthick loop carpet.…”

“…8,9 Second, peak impact forces during simulated falls are reduced between 7 and 23% by compliant floor designs. [10][11][12] However, in the studies providing this evidence falls were simulated with a mechanical test system, which may not accurately measure the force attenuation provided by the floor during falls in humans. Furthermore, data on the stiffness of the tested floor conditions were not reported.…”

Load on Osseointegrated Fixation of a Transfemoral Amputee during a Fall

“…Thankfully, no injuries to the participant and damage to the fixation occurred indicating that the severity of the forward fall was low. Indeed, the maximum force on impact was approximately four times smaller than the force required for a femoral neck and intertrochantric fractures during sideways fall (40)(41)(42)(43)(44) . Furthermore, the transition between loading and descent phases might present different patterns on each axis depending on the severity and type of fall (e.g., backward, sideways).…”

Load on Osseointegrated Fixation of a Transfemoral Amputee During a Fall

“…The typical approach relies on simulation of the impact on the fixation using a jig and/or finite element models. [16][17][18][19][20] However, such experiments are only partially realistic since the load applied during a real fall is currently unknown.…”

“…Load during a fall of a transfemoral amputeefall. [16][17][18][19][20] Backward falls might create larger bending moments when the prosthetic leg remains tucked under the thigh during the impact.…”