Citation

Laing AC, Robinovitch SN. J. Biomech. 2010; 43(10): 1898-1904.

Affiliation

Injury Prevention and Mobility Laboratory, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada V5A 1S6; Department of Kinesiology, University of Waterloo, 200 University Ave West, Waterloo, Ontario, Canada N2L 3G1.

Copyright

(Copyright © 2010, Elsevier Publishing)

DOI

10.1016/j.jbiomech.2010.03.025

PMID

20398905

Abstract

The force applied to the proximal femur during a fall, and thus hip fracture risk, is dependent on the effective stiffness of the body during impact. Accurate estimates of pelvis stiffness are required to predict fracture risk in a fall. However, the dynamic force-deflection properties of the human pelvis have never been measured in-vivo. Our objectives were to (1) measure the force-deflection properties of the pelvis during lateral impact to the hip, and (2) determine whether the accuracy of a mass-spring model of impact in predicting peak force depends on the characterization of non-linearities in stiffness. We used a sling and electromagnet to release the participant's pelvis from heights up to 5cm, simulating low-severity sideways falls. We measured applied loads with a force plate, and pelvis deformation with a motion capture system. In the 5cm trials peak force averaged 1004 (SD 115)N and peak deflection averaged 26.3 (5.1)mm. We observed minimal non-linearities in pelvic force-deflection properties characterized by an 8% increase in the coefficient of determination for non-linear compared to linear regression equations fit to the data. Our model consistently overestimated peak force (by 49%) when using a non-linear stiffness equation, while a piece-wise non-linear fit (non-linear for low forces, linear for loads exceeding 300N) predicted peak force to within 1% at our highest drop height. This study has important implications for mathematical and physical models of falls, including mechanical systems that assess the biomechanical effectiveness of protective devices aimed at reducing hip fracture risk.

Language: en