Predicting the strength of femoral shafts with and without metastatic lesions.

To evaluate a potential tool for assessing the risk of a pathologic fracture of the femoral shaft, we examined whether fracture loads computed by our computed tomography scan-based finite element models are predictive of measured fracture loads. We also evaluated whether the precision of the computed fracture loads for shafts with metastases is altered if models are generated using mechanical property-density relationships for bone without metastases. We investigated whether femoral shafts with a hemispheric defect and shafts with metastases have qualitatively similar structural behavior. Using identical four-point bending loading conditions, we computed and measured fracture loads of femoral shafts with and without metastases and with a burred hemispheric defect to simulate a tumor. Finite element model fracture loads were strongly predictive of the measured fracture loads (range, 0.92-0.98) even when the models of bones with metastases used mechanical property relationships for bone without metastases. Specimens with hemispheric defects behaved structurally differently than specimens with metastases, indicating that these defects do not accurately simulate the effects of metastases. Results of our study show that these computed tomography scan-based finite element models can be used to estimate the strength of femoral shafts with and without metastases. These models may be useful for assessing the risk of pathologic fractures of femoral shafts.