Experimental validation of finite element predicted bone strain in the human metatarsal

Anita Fung,Lindsay L Loundagin,W Brent Edwards

doi:10.1016/j.jbiomech.2017.06.010

Abstract

Metatarsal stress fracture is a common injury observed in athletes and military personnel. Mechanical fatigue is believed to play an important role in the etiology of stress fracture, which is highly dependent on the resulting bone strain from the applied load. The purpose of this study was to validate a subject-specific finite element (FE) modeling routine for bone strain prediction in the human metatarsal. Strain gauge measurements were performed on 33 metatarsals from seven human cadaveric feet subject to cantilever bending, and subject-specific FE models were generated from computed tomography images. Material properties for the FE models were assigned using a published density-modulus relationship as well as density-modulus relationships developed from optimization techniques. The optimized relationships were developed with a ‘training set’ of metatarsals (n=17) and cross-validated with a ‘test set’ (n=16). The published and optimized density elasticity equations provided FE-predicted strains that were highly correlated with experimental measurements for both the training (r2≥0.95) and test (r2≥0.94) sets; however, the optimized equations reduced the maximum error by 10% to 20% relative to the published equation, and resulted in an X=Y type of relationship between experimental measurements and FE predictions. Using a separate optimized density-modulus equation for trabecular and cortical bone did not improve strain predictions when compared to a single equation that spanned the entire bone density range. We believe that the FE models with optimized material property assignment have a level of accuracy necessary to investigate potential interventions to minimize metatarsal strain in an effort to prevent the occurrence of stress fracture.

Highlights

Stress fractures are common injuries in athletic and military populations
The published density-modulus equation provided finite element (FE)-predicted strains (Figure 4b) that were highly correlated with experimental measurements for both the training (r2=0.95) and test (r2=0.94) set (Table 2)
The published density-modulus equation provided metatarsal strain predictions that were highly correlated with experimental measurements (r2 0.94), in accordance with some of the better FE predictions reported in the literature for other bones (Barker et al, 2005; Gray et al, 2008; Schileo et al, 2007; Trabelsi et al, 2014)

Summary

Introduction

Stress fractures are common injuries in athletic and military populations. This type of fracture makes up 10% of athletic injuries (Matheson et al, 1987), and up to 31% of injuries experienced by military recruits (Milgrom et al, 1985). In the US Marine Corps, stress fractures are the single most costly injury ($5 million per year) due to lost training time, medical and rehabilitation expenses, and trainee attrition (Almeida et al, 1997). Mechanical fatigue is a well-accepted proposed mechanism in the pathophysiology of stress fracture (Burr et al, 1997; Carter et al, 1981; Schaffler et al, 1989). Mechanical fatigue is defined as the progressive loss of material stiffness and strength due to repetitive loading

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