In silico finite element modelling (FEM) in the realm of femur trauma

Introduction
Pertrochanteric femur fractures are bone traumas that are difficult to manage, with a substantial rate of union failure. Excessive stress exerted on the fragmented bones can cause nonunion, which requires salvage surgery. Bone stress as the underlying mechanism of nonunion is as yet unassessable, which makes it difficult to choose the method of restabilisation.

Aim of the research
We adopted an innovative method of in silico finite element modelling (FEM) to retrospectively simulate the pattern of stabiliser-bone stress distribution changes in proximal femur fractures, which may underlie the lack of osteosynthesis necessitating salvage surgery.

Material and methods
FEM concerned proximal femur A2 and A3 fractures in elderly patients who required restabilisation due to a failure to achieve union. The modelling was entirely virtual, with no patient involvement at any stage, and based on X-ray bone contour projections. We chose the non-standard ZESPOL method for restabilisation, in which the stabilising system is mounted about 10 mm apart from the bone surface.

Results
FEM showed the presence of substantial stabiliser-bone stress before achieving the union. ZESPOL stabilisation equalised and reduced stress, ending up in a full union.

Conclusions
An outstanding difference in stress distribution between the conditions of nonunion and union after salvage surgery reaffirms the conceptual basis for the stress-induced role in union failure. ZESPOL is viable stabilisation in difficult-to-treat conditions of pertrochanteric fracture nonunion. FEM can help in decision-making concerning the type of surgical repair needed for the optimal disburdening of compressive stress to accelerate osteosynthesis.