Elsevier

Journal of Biomechanics

Volume 63, 3 October 2017, Pages 174-178
Journal of Biomechanics

Short communication
An ex vivo experiment to reproduce a forward fall leading to fractured and non-fractured radii

https://doi.org/10.1016/j.jbiomech.2017.08.013Get rights and content

Abstract

Forward falls represent a risk of injury for the elderly. The risk is increased in elderly persons with bone diseases, such as osteoporosis. However, half of the patients with fracture were not considered at risk based on bone density measurement (current clinical technique). We assume that loading conditions are of high importance and should be considered. Real loading conditions in a fall can reach a loading speed of 2 m/s on average. The current study aimed to apply more realistic loading conditions that simulate a forward fall on the radius ex vivo. Thirty radii from elderly donors (79 y.o. ± 12 y.o., 15 males, 15 females) were loaded at 2 m/s using a servo-hydraulic testing machine to mimic impact that corresponds to a fall. Among the 30 radii, 14 had a fracture after the impact, leading to two groups (fractured and non-fractured). Surfacic strain fields were measured using stereovision and allow for visualization of fracture patterns. The average maximum load was 2963 ± 1274 N. These experimental data will be useful for assessing the predictive capability of fracture risk prediction methods such as finite element models.

Introduction

Among the different bone fractures, those of the distal section of the radius occur earlier in life than other osteoporotic fractures and can be interpreted as a warning signal for later, more deleterious fractures (Melton et al., 2010). The gold standard method for clinical diagnosis of osteoporosis and evaluation of the risk for fracture is Dual X-ray Absorptiometry (DXA) (World Health Organization, 2004). It has been shown, however, that this measurement presents insufficient sensitivity, and indeed 50% of fractures occur in patients considered as non-osteoporotic (Siris et al., 2004).

Ongoing research has proposed different methods to improve sensitivity. One of these methods is analysis by micro-finite element models (µFEM) based on High Resolution peripheral Quantitative Computed Tomography (HR-pQCT) (Pistoia et al., 2002, Vilayphiou et al., 2011). All validation studies have shown that bone strength is better estimated by µFEM (R2 between 0.73 and 0.92) than by DXA measurements (R2 between 0.31 and 0.71) (van Rietbergen and Ito, 2015). Despite this good level of prediction of bone strength using µFEM, retrospective studies have not yet provided clear evidence that the output of µFEM provides better predictors of fracture risk than DXA measurements (van Rietbergen and Ito, 2015).

Currently, the assessment of bone fragility using HR-pQCT implies a finite element analysis under static axial loading (Pistoia et al., 2002, Macneil and Boyd, 2008, Varga et al., 2009, Hosseini et al., 2017). However, only 15% of fall cases are associated with an axial load on the radius (Melton et al., 2010) and asymmetrical body orientation influences loading of the radius (Burkhart et al., 2017). The most common angle between the floor and the arm found in the forward fall is 75° (Greenwald et al., 1998, Chiu and Robinovitch, 1998) and the average velocity when the subject hits the floor can reach 2 m/s (Tan et al., 2006, Troy and Grabiner, 2007). Thus, we assume that this dynamic loading should be considered for ex vivo experiments that result in fractured and non-fractured bones. Having these two groups in known loading conditions would be of interest to assess new methodologies to predict bone fracture risk.

Previous studies loaded radii until failure in all cases, with some under quasi-static conditions (Pistoia et al., 2002, Macneil and Boyd, 2008, Varga et al., 2009, Hosseini et al., 2017) and one using fall conditions (Burkhart et al., 2012). In this context, the aim of this study is to propose an ex vivo experiment to reproduce a forward fall loading condition, leading to fractured and non-fractured radii.

Section snippets

Methods

Thirty radii from elderly donors (50–96 y.o., 79 ± 12 y.o., 15 males, 15 females) were considered. The bones were provided by the Departement Universitaire d’Anatomie Rockefeller (Lyon, France) through the French program on voluntary corpse donation to science. First, during the dissection, 2/3 of the distal radius was cut and cleaned of soft tissues. Each radius was wrapped in a saline-moistened gauze and frozen at −20 °C before the experiments.

The day before the experiments, bones were thawed

Maximum loads from the experiment

Maximum loads are shown in Table 1 and correspond to the failure loads for the fractured cases. Fractures were not consistently associated with the largest loads and depended on bone strength. Stronger bones can indeed sustain larger loads before breaking.

Fracture cases and type of fracture

Among the 30 radii, 14 had a fracture after impact, and 16 did not fracture. In three cases over the 14 fracture cases the radius were not classified as osteoporotic according to DXA measurements.

The type of fracture is indicated in Table 1.

Discussion

This study provided experimental data reproducing a forward fall on the radius leading to fractured and non-fractured bones.

The average values of the experimental peak loads in the current study: 2963 (1274) N are in agreement with those reported in the literature: 2142 (1229) N (Burkhart et al., 2014). When observing the high-speed videos, it was found that among the 30 radii, some of them presented a sliding effect of the mold over the articular surface. This effect could be related to the

Conclusions

Thirty radii were tested under dynamic non-axial loading to reproduce a forward fall configuration. Most previous studies have evaluated bone strength of the radius under static conditions and until failure in all cases. The originality of the current study is related to the two groups of bones (fractured and non-fractured). Having these two groups with known loading conditions is of great interest to assess the predictive capability of finite element models and to check whether consideration

Acknowledgements

The authors would like to acknowledge Leila Ben Boubaker for her assistance during the experiments, Jean-Paul Roux, Yves Caire and Stéphane Ardizzone for their technical support. This work was done in the framework of LabEx PRIMES (ANR-11-LABX-0063).

Conflict of interest

There is no conflict of interest for any of the authors.

Cited by (5)

  • A credible homogenized finite element model to predict radius fracture in the case of a forward fall

    2022, Journal of the Mechanical Behavior of Biomedical Materials
    Citation Excerpt :

    Images were reconstructed with a field of view of 8.16 cm and a matrix of 544 × 544 to give a reconstructed isotropic voxel size of 150 μm. The experimental protocol used here was previously described in detail by Zapata et al. (2017). The day before the experiments took place, bones were thawed for 16 h at 4°C and then 6 h at room temperature.

  • Influence of loading conditions in finite element analysis assessed by HR–pQCT on ex vivo fracture prediction

    2022, Bone
    Citation Excerpt :

    Considering that forearm fractures were almost exclusively caused by a fall from a standing height in a forward direction [18–20] and that boundary conditions have a large effect on radius fracture load in continuum finite element models [21,22] loading orientation should be considered as a non-axial impact on the wrist, which differs from the axial compression utilized in HR–pQCT μFE analysis. In this context, the objective of this study is to compare the axial compression currently used with other loading modes to discriminate fractured radius from non-fractured radius obtained in a previous ex vivo experimental study reproducing a forward fall under dynamic loading conditions [23]. Thirty fresh–frozen cadaveric left radii from elderly donors (50–96 y.o., 79 ± 12 y.o., 15 males, 15 females) provided by the University Department of Anatomy Rockefeller (Lyon, France) were considered for this study (French Ministry of Education and Research, authorization no. DC–2015–2357).

  • Impact testing of snowboarding wrist protectors

    2023, Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology
View full text