Finite element modelling of butterfly fractures in a long bone

Abstract

Butterfly fracture occurs most frequently among the various long bone fracture pattern during blunt force trauma such as traffic accidents. It is also a factor of interest in forensic investigation to construct the crime scene. It is hypothesized that bending is the main reason behind the formation of butterfly fractures. However, there is no simple relationship between bending and butterfly fracture as bending can cause other fracture patterns such as transverse and oblique fracture patterns.

The objective of this project is to investigate the effect of loading conditions to form butterfly fracture in long bone using finite element method (FEM). Modelling was carried out in ABAQUS/CAE and the problem was solved using ABAQUS/Explicit. Brittle cracking and concrete damaged plasticity were used as the material behaviour of the cortical bone in the simulation. The FEM model underwent three-point and four-point bending with various bluntness of impactors. Furthermore, the effect of axial loading is studied.

In this report, significant advancement is made to produce butterfly fracture in long bone. The results supported that failure originates at the tension side of the long bone during bending. Asymmetrical material properties are likely to allow tension failure before compression failure at the point of impact. The presence of axial loading or arc-shaped long bone may assist in the branching of the main crack and provide a bigger wedge. Blunt impacts seem to be more likely to produce butterfly facture. Lastly, with minimum interference from the site of impact, a complete butterfly fracture can be produced.