A comparative finite element study of condylar fixation: preliminary results

The basis for fixation of condylar fractures is strongly determined by surgical decision using available technology. Recent developments of technology include the retrograde distal femoral nail (DFN), with condylar "bolts" (T2 SCN), and along with the dynamic condylar screw (DCS) and various combinations of additional screws and wire, these devices form the primary elements available for fracture fixation. This paper looks at the relative structural performance of these constructs under the action of an idealised loading condition -- axial load through the femoral head in line with the mechanical (c.f. anatomical) axis of the femur. The finite element method is used. The geometric models have been created using available published information, and meshing generated using tetrahedral elements. Some reasonable assumptions about the properties of cortical and cancellous bone have been made. The effect of good quality and poor quality cancellous bone has been considered. The results show the displacements of each device and some of the key stressed regions using each construct principle. The use of condylar bolts produces significant levels of stress within the bone before any patient-load is applied, but provides a stiffer construct for subsequent loading. Surgeons will make their own decisions about the appropriate construct for each patient, but this evaluation is intended to help with that decision making.