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Research Papers

Finite Element Modeling of the Influence of Hand Position and Bone Properties on the Colles’ Fracture Load During a Fall

[+] Author and Article Information
Drew Buchanan

Department of Mechanical Engineering, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085

Ani Ural1

Department of Mechanical Engineering, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085ani.ural@villanova.edu

1

Corresponding author.

J Biomech Eng 132(8), 081007 (Jun 18, 2010) (8 pages) doi:10.1115/1.4001681 History: Received July 28, 2009; Revised April 01, 2010; Posted April 28, 2010; Published June 18, 2010; Online June 18, 2010

Distal forearm fracture is one of the most frequently observed osteoporotic fractures, which may occur as a result of low energy falls such as falls from a standing height and may be linked to the osteoporotic nature of the bone, especially in the elderly. In order to prevent the occurrence of radius fractures and their adverse outcomes, understanding the effect of both extrinsic and intrinsic contributors to fracture risk is essential. In this study, a nonlinear fracture mechanics-based finite element model is applied to human radius to assess the influence of extrinsic factors (load orientation and load distribution between scaphoid and lunate) and intrinsic bone properties (age-related changes in fracture properties and bone geometry) on the Colles’ fracture load. Seven three-dimensional finite element models of radius were created, and the fracture loads were determined by using cohesive finite element modeling, which explicitly represented the crack and the fracture process zone behavior. The simulation results showed that the load direction with respect to the longitudinal and dorsal axes of the radius influenced the fracture load. The fracture load increased with larger angles between the resultant load and the dorsal axis, and with smaller angles between the resultant load and longitudinal axis. The fracture load also varied as a function of the load ratio between the lunate and scaphoid, however, not as drastically as with the load orientation. The fracture load decreased as the load ratio (lunate/scaphoid) increased. Multiple regression analysis showed that the bone geometry and the load orientation are the most important variables that contribute to the prediction of the fracture load. The findings in this study establish a robust computational fracture risk assessment method that combines the effects of intrinsic properties of bone with extrinsic factors associated with a fall, and may be elemental in the identification of high fracture risk individuals as well as in the development of fracture prevention methods including protective falling techniques. The additional information that this study brings to fracture identification and prevention highlights the promise of fracture mechanics-based finite element modeling in fracture risk assessment.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Traction-displacement relationship defining the cohesive zone model in shear and normal modes. Note that the subscript n refers to the normal direction and the subscripts t and s refer to the two in-plane shear directions. tn is the normal, ts and tt are the shear tractions transferred between the crack surfaces. δn is the normal, δs and δt are the shear crack opening displacements. δnu, δsu, and δtu denote the ultimate values of the crack opening displacements. Note that due to the assumption of same in-plane shear behavior in both directions, the variables associated with the t- and s-directions are equal. (b) Tetrahedral solid elements and the compatible wedge shaped cohesive element with six nodes.

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Figure 2

(a) A 2D anatomical sketch of the radius, ulna, scaphoid, and lunate. The dotted lines indicate the region that was modeled in the finite element simulations. (b) A sample 3D finite element mesh of the radius. The load is applied at the most distal surface of the bone. The load transferred from scaphoid and lunate is shown by the right (scaphoid) and left (lunate) sections on the top surface.

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Figure 3

Fracture load versus load angle between the resultant force and the (a) longitudinal, (b) dorsal, (c) lateral axes for all geometries. Note that all the load orientation cases were run for geometries 3 and 7. For the remaining geometries, only three cases were run. All plots are for uniform load distribution between scaphoid and lunate and with fracture properties for 50 years of age. The r2 values for geometries 3 and 7 in (a) and (b) correspond to quadratic fits of the data points. There was no statistically significant relationship in (c). Note that the inset shown in the figures denote the angle plotted in each figure, where A, D, and L axes labels refer to longitudinal, dorsal, and lateral directions, respectively.

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Figure 4

Fracture load versus load distribution ratio between lunate and scaphoid (lunate/scaphoid) for all geometries under a constant load orientation (corresponding to orientation 7 in Table 2) and with fracture properties for 50 years of age. Note that for geometries 3 and 7, all the load ratio cases were run. For the remaining geometries only three cases were run. The r2 values for geometries 3 and 7 correspond to linear fits of the data points.

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Figure 5

Fracture load versus load angle between the resultant force and the longitudinal axis for a load ratio of 0.25 and for 50, 70, and 90 years of age. All fits are quadratic with r2 values of 0.96, 0.96, and 0.94, for 50, 70, and 90 years, respectively.

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Figure 6

Fracture load versus cortical polar moment of inertia for two different load ratios (lunate/scaphoid) and load angles between the resultant force and the longitudinal axis using fracture properties for 50 years of age. Note that the first number next to each line denotes the load angle between the longitudinal axis and the resultant force, and the second number denotes the load distribution ratio between lunate and scaphoid (lunate/scaphoid). The solid lines denote the mean polar moment of inertia for men (right) and women (left) (46), whereas the dotted lines indicate the standard deviation of the mean values.

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