EFFECT OF CALLUS OSSIFICATION AND EXTRAOSSEOUS FORMATION ON THE MECHANICAL PERFORMANCE OF INTERNAL FIXATION SYSTEMS

An investigation into the effect of extraosseous formation around an internal fixation plate (long bone mid-shaft) and callus ossification on the localalized stress distribution in the periosteum is performed. An analytical model of the system is developed; predicted trends are compared with Finite Element (FE) model predictions. Both models are described and the limitations relevant to their predictions are discussed. Two load cases are examined: pure bending and bending coupled with compression. Both models indicate that the presence of the plate results in stress shielding for both load cases. For the pure bending case, the analytical model predicts that the extraosseous formation serves to reduce the level of stress shielding caused by the plate, while the FE model predicts an increase. Both models predict that the presence of callus serves to further increase stress shielding, however the magnitude of the effect of the callus on the tension side of the bone differs substantially between models. Further refinement of both models is recommended.