Short communicationAn ex vivo experiment to reproduce a forward fall leading to fractured and non-fractured radii
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.
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