Keywords: medical, bone, femur, fracture, gamma nail, finite element, Delaunay triangulation, tetrahedral elements.

Medical engineering is an area of research that is growing in importance in order to increase understanding of the human body and improve medical techniques and care. 85% of femoral fractures occur as a result of low energy trauma in patients over 50 years of age [1]. One of the principal causes of mortality and morbidity among the elderly is the fracture of the proximal femur [2] and the treatment of choice is surgical, with the trochanteric gamma nail being the preferred implant.

The work presented in this paper aims to improve on an existing three dimensional finite element (FE) femoral model which incorporates a trochanteric gamma nail [3,4,5]. The main modification of this work includes the insertion of an initial fracture into the bone material of the femur that is to be repaired by the implanted trochanteric gamma nail. The initial fracture passes only through the bone material and not the implant. Since the outer elements of the bone share nodes with the implant, it was necessary to identify the nodes of the implant and exclude them from the fracture surface. This was done using a recursive colouring procedure.

Two initial undisplaced fractures were modelled to asses the suitability of the implant for repairing each fracture type. The types of fractures modelled were inter-trochanteric and sub-trochanteric fractures. The modified models were then run to investigate the likelihood of re-fracture and the subsequent fracture patterns produced by impact from a fall. The results show that due to the fracture patterns and higher stresses produced, an inter-trochanteric fracture is less stable and more at risk of sever re-fracture following a fall.

Continuing and further work includes refining the pre-processing code in order to take greyscale values for each point in the geometry directly from CT scan voxel data instead of interpolating between z-layer contours. This will improve the CPU time and increase the accuracy of the model.

1

D.G. Dunlop and I.J. Brenkel, "The supracondylar intramedullary nail in elderly patients with distal femoral fractures", Injury, 1999. 30(7): pp. 475-484. doi:10.1016/S0020-1383(99)00136-9

2

D. Testi, M. Viceconti, F. Baruffaldi and A. Cappello, "Risk of fracture in elderly patients: a new predictive index based on bone mineral density and finite element analysis", Computer Methods and Programs in Biomedicine, 1999. 60: pp. 23-33. doi:10.1016/S0169-2607(99)00007-3

3

C.A. Pridham, "Tetrahedral finite element (FE) meshes to model femoral fractures generated from CT scans form the Visible Human Project", MRes Thesis, University of Wales, Swansea, 2004.

4

T.D. Fawcett, "Creating and validating heterogeneous tetrahedral finite element models of the femur from Computed Tomography (CT images)", MRes Thesis, University of Wales, Swansea, 2004.

5

M. Barclay, "Bone fracture in the femur: Numerical model with the inclusion of a gamma nail implant", MRes Thesis, University of Wales, Swansea, 2006.

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