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The risk of hip fracture is reduced around 40 percent for elderly men and women with a compliant pavement
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.ORCID iD: 0000-0001-6923-4751
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.ORCID iD: 0000-0003-0125-0784
2022 (English)In: Article in journal (Other academic) Submitted
Abstract [en]

Older adults are at more significant risk of hip fracture when they fall. In addition to the higher risk of falls for the elderly, fear of falls can reduce this population's outdoor activity. Various preventive solutions were proposed to reduce the risk of hip fractures ranging from wearable hip protectors to indoor flooring systems. A previously developed rubberized asphalt mixture demonstrated the potential to reduce the risk of head injury. In the current study, the capability of the rubberized asphalt sample was evaluated for the risk of hip fracture for an average elderly man and an average elderly woman. A previously developed human body model was positioned in a fall configuration that would give the highest impact forces towards regular asphalt. Three different rubber contents with 14, 28, 33 % wt. were implemented as the ground alongside a reference non-rubberized (0%) asphalt mixture and regular and compliant playground rubber-composite materials. The whole-body model was simulated to fall on the rubberized asphalt mixtures with an initial vertical velocity of 3 m/s with a 10-degree trunk angle and +10 degree anterior pelvis rotation. The impact forces were measured on the femoral head, and a previously developed hip fracture risk function was used to compare the rubberized asphalt mixtures. It was found that the rubberized asphalt mixture with 33 % wt. rubber can reduce the impact forces up to 10 percent for the elderly male and female model compared to regular asphalt. The impact forces were most reduced for the compliant playground material, with a 23% reduction for the female model. The risk of injury for the asphalt mixture with 33% wt. rubber was reduced up to 18 percent for elderly women and 20 for elderly men, compared to regular asphalt. The compliant playground material had the most reduction of hip fracture risk for both sexes, 39 and 43 percent for elderly women and men, respectively.

Place, publisher, year, edition, pages
2022.
Keywords [en]
Hip fracture, Whole-body model, Fracture prevention, compliant pavement, Vulnerable Road User
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-311604OAI: oai:DiVA.org:kth-311604DiVA, id: diva2:1655142
Note

QC 20220504

This study was jointly supported by a grant from "BVFF – Bana väg för framtiden" (BVFF number 2016-025) and Sweden's innovation agency, Vinnova (D.nr.: 2013-04465, 2021-01598). The simulations were performed on resources provided by the Swedish National Infrastructure for Computing(SNIC) at the center for High-Performance Computing (PDC).

Available from: 2022-04-30 Created: 2022-04-30 Last updated: 2024-03-18Bibliographically approved
In thesis
1. Biomechanical Analysis of Fall Injuries using Finite Element Modeling
Open this publication in new window or tab >>Biomechanical Analysis of Fall Injuries using Finite Element Modeling
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A fall is a serious health issue for the elderly. Among different fall types, the sideways fall is considered to be more severe concerning the injury outcome. When elderlies experience an unintentional sideways fall, they can either resist the impact forces with the soft tissue force attenuation capacity and femoral strength or need external protections to reduce the injury risk. In this thesis, these two aspects were investigated. Finite element whole-body models are valuable tools for analyzing fall biomechanics and investigating the possible preventive measures more conveniently. The whole-body models were developed to investigate traffic accidents; however, a sideways fall has different kinematics than the other types of accidents. Consequently, it is necessary to enhance the whole-body models according to the major fall parameters leading to severe injury cases before assessing the external protection capabilities.The current thesis attempted to advance these two critical aspects regarding fall-induced injuries. A finite element whole-body model was chosen to study three critical parameters in fall biomechanics: body posture, soft tissue, and femoral strength. The whole body model was positioned in different body configurations relevant for the sideways fall to evaluate the body posture that could lead to the highest internal forces on the femoral head. Next, different soft tissue constitutive material models and soft tissue thicknesses were investigated to find a material model that could accurately reproduce the experimental results according to an objective rating method named CORrelation and Analysis (CORA). Finally, the separate and combined effects of geometrical and mechanical properties change due to aging on femoral strength were assessed for the elderly males and females. In the second aspect of the thesis, the shock-absorbing rubberized asphalt pavements' preventive capacity was examined. First, different rubberized asphalt mixtures were implemented in a bicycle and a pedestrian accident reconstruction cases to evaluate the head injury risks. Later, the asphalt mixtures were studied in a sideways fall scenario to evaluate the hip fracture risk in an elderly male and female.

The first aspect of the thesis presented the results and methods to improve the sideways fall analysis, and the second aspect of the thesis focused on assessing the rubberized asphalt mixtures for injury prevention purposes. The sideways fall with the upright trunk and a slightly forward-tilted pelvis could lead to the highest internal forces. A nonlinear Ogden material model for muscle tissue and a Mooney-Rivlin material model for adipose tissue scored better among different soft tissue material models in the side impacts to the hip segments. The geometrical and mechanical properties change due to aging leading to a different behavior for males and females, where females experience a higher rate of strength loss due to aging. Moreover, it was indicated that a rubberized asphalt mixture could reduce the head injury risk for pedestrians and cyclists and the hip fracture risk for the elderly. The amount of rubber in the asphalt mixtures needs to exceed a specific limit to observe rubberized asphalts' preventive effects. Consequently, it is necessary to optimize the mixtures' rubber content to improve its prevention capacity.

In summary, the current thesis presented a method to improve the whole-body models according to the sideways fall requirements and assessed the protective capacity of the rubberized asphalt mixtures against head and hip injuries.

Abstract [sv]

Ett fall är ett allvarligt hälsoproblem för äldre. Bland olika falltyper anses fallet i sidled vara allvarligare vad gäller skadeutfallet. När äldre drabbas av ett oavsiktligt fall i sidled kan de antingen stå emot slagkrafterna med mjukvävnadskraftens dämpningsförmåga och lårbensstyrka eller behöva yttre skydd för att minska skaderisken. I denna avhandling har dessa två aspekter undersökts. Finite element helkroppsmodeller är värdefulla verktyg för att analysera falls biomekanik och lämpligt för att undersöka möjliga förebyggande åtgärder mer bekvämt. Helkroppsmodellerna utvecklades för att undersöka trafikolyckorna; ett fall i sidled har dock en annan kinematik än de andra typerna av olyckor. Följaktligen är det nödvändigt att förbättra helkroppsmodellerna enligt de viktigaste fallparametrarna, vilket leder till allvarliga skadefall, innan man bedömer de yttre skyddsförmågan.

Den aktuella avhandlingen försökte föra fram dessa två kritiska aspekter angående fallinducerade skador. En finite element helkroppsmodell valdes för att studera tre kritiska parametrar i falls biomekanik: kroppshållning, mjukvävnad och femoral styrka. Helkroppsmodellen placerades i olika kroppskonfigurationer som är relevanta för fallet i sidled för att utvärdera kroppshållningen som kunde leda till de högsta inre krafterna på lårbenshuvudet. Därefter undersöktes olika konstitutiva materialmodeller för mjukvävnad och mjukdelstjocklekar för att hitta en materialmodell som exakt kunde återge de experimentella resultaten enligt en objektiv klassificeringsmetod som heter CORrelation and Analysis (CORA). Slutligen utvärderades de separata och kombinerade effekterna av förändringar av geometriska och mekaniska egenskaper på grund av åldrande på lårbensstyrkan för äldre män och kvinnor. I den andra aspekten av avhandlingen undersöktes de stötdämpande gummerade asfaltbeläggningarnas förebyggande kapacitet. Först implementerades olika gummerade asfaltblandningar i rekonstruktionsfallen för en cykel och en fotgängarolycka för att utvärdera riskerna för huvudskador. Senare studerades asfaltblandningarna i ett sidledes fallscenario för att utvärdera risken för höftfraktur hos en äldre man och kvinna.

Den första aspekten av avhandlingen presenterade resultaten och metoderna för att förbättra analysen av sidledsfall, och den andra aspekten av avhandlingen fokuserade på att bedöma de gummerade asfaltblandningarna i skadeförebyggande syfte. Fall i sidled med upprätt bål, och ett något framåtlutat bäcken kan leda till de högsta inre krafterna. En ickelinjär Ogden-materialmodell för muskelvävnad och en Mooney-Rivlin-materialmodell för fettvävnad fick bättre poäng bland olika mjukdelsmaterialmodeller i sidokollisioner mot höftsegmenten. De geometriska och mekaniska egenskaperna förändras på grund av åldrande vilket leder till ett annorlunda beteende för män och kvinnor där kvinnor upplever en högre grad av förlust i styrka på grund av åldrande. Dessutom indikerades att en gummerad asfaltblandning kunde minska risken för huvudskador för fotgängare och cyklister och risken för höftfraktur för äldre. Mängden gummi i asfaltblandningarna behöver överskrida en specifik gräns för att observera gummerad asfalts förebyggande effekt. Följaktligen är det nödvändigt att optimera blandningarnas gummihalt för att förbättra dess förebyggande förmåga.

Sammanfattningsvis presenterade den aktuella avhandlingen en metod för att förbättra helkroppsmodellerna enligt kraven på sidledes fall och bedömde skyddsförmågan hos de gummerade asfaltblandningarna vid huvud- och höftskador.

Place, publisher, year, edition, pages
Sweden: KTH Royal Institute of Technology, 2022. p. 56
Series
TRITA-CBH-FOU ; 2022:29
Keywords
Fall induced injury, finite element analysis, rubberized asphalt mixture, shock-absorbing pavement, hip fracture, elderly, sideways fall, whole-body model
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-311606 (URN)978-91-8040-211-8 (ISBN)
Public defence
2022-05-23, Rappesalen, Alfred Nobels Allé 10, Huddinge, 14:00 (English)
Opponent
Supervisors
Note

The thesis was carried out at the Neuronic Engineering unit, KTH Royal Institute of Technology in Stockholm, Sweden. The thesis was funded by "BVFF – Bana väg för framtiden" (BVFF number 2016-025).

QC 2022-05-02

Available from: 2022-05-02 Created: 2022-04-30 Last updated: 2022-06-25Bibliographically approved

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Sahandifar, PooyaKleiven, Svein

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