Density predicts the activity-dependent failure load of proximal femora with defects

Abstract 

Objective. To determine whether the load-bearing capacity of human proximal femora with metastatic defects can be predicted from the bone mineral content. Design. The bone mineral content (BMC) of the total proximal femur was measured by dual-energy X-ray absorptiometry (DXA). The femurs were loaded so as to simulate stair ascent or external rotation. Patients. Simulated lytic defects were created using specialized cutting tools in the intertrochanteric region of 32 human cadaveric femora. Bone density measurements were made before and after creating defects. Results. A linear relation could be used to predict failure load from BMC or bone mineral density. The slope of the linear relation was greater for loads representing external rotation than for loads representing stair ascent. The linear relations suggest that the BMC measurements account for both the density of the host bone and the amount of bone removed by the defect. Conclusions. The data suggest that between 70% and 80% of the variation in failure load of human femora with lytic metastatic defects can be predicted from the BMC and that relations between BMC and failure load are sensitive to the type of loading. Combined with information on the loads associated with the activities of daily living, these data may be used to help identify patients in whom prophylactic stabilization might prevent a pathologic fracture.