Citation

Fleps I, Guy P, Ferguson SJ, Cripton PA, Helgason B. J. Bone Miner. Res. 2019; ePub(ePub): ePub.

Affiliation

Institute for Biomechanics, ETH Zürich, Zürich, Switzerland.

Copyright

(Copyright © 2019, American Society for Bone and Mineral Research)

DOI

10.1002/jbmr.3804

PMID

31163090

Abstract

The majority of hip fractures in the elderly are the result of a fall from standing or from a lower height. Current injury models focus mostly on femur strength while neglecting subject-specific loading. This article presents an injury modelling strategy for hip fractures related to sideways falls that takes subject-specific impact loading into account. Finite element models (FEMs) of the human body were used to predict the experienced load and the femoral strength in a single model. We validated these models for their predicted peak force, effective pelvic stiffness, and fracture status against matching ex vivo sideways fall impacts (N=11) with a trochanter velocity of 3.1 m/s. Furthermore, they were compared to sideways impacts of volunteers with lower impact velocities that were previously conducted by another group. Good agreement was found between the ex vivo experiments and the FEMs with respect to peak force (RMSE=10.7 %, R2=0.85) and effective pelvic stiffness (R² =0.92, RMSE=12.9 %). The FEMs were predictive for the fracture status of ten out of elven specimens. Compared to the volunteer experiments from low height, the FEMs overestimated the peak force by 25% for low BMI subjects and 8% for high BMI subjects. The effective pelvic stiffness values that were derived from the FEMs were comparable to those derived from impacts with volunteers. The force attenuation from the impact surface to the femur ranged between 27-54% and was highly dependent on soft tissue thickness (R² =0.86). The energy balance in the FEMS showed that at the time of peak force 79 - 93 % of the total energy is either kinetic or was transformed to soft tissue deformation. The presented FEMs allow for direct discrimination between fracture and non-fracture outcome for sideways falls and bridge the gap between impact testing with volunteers and impact conditions representative of real life falls. This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

Language: en

Keywords

Biomechanics, ORTHOPAEDICS; Fracture prevention, PRACTICE/POLICY-RELATED ISSUES; Fracture risk assessment, PRACTICE/POLICY-RELATED ISSUES