PREDICTING PATHOLOGICAL FRACTURE RISK IN THE MANAGEMENT OF METASTATICBONE DEFECTS

Guidelines for the prediction of pathologic fracture would facilitate the management of patients with metastatic bone defects. Unfortunately , existing clinical guidelines have not been validated, often run coun ter to engineering practice, and do not accurately predict the risk of fracture for many patients. To serve as a basis for improved guidelin es, a factor of risk for a pathologic fracture is defined as the load applied to a bone divided by the load at which the bone fails. Failure loads for bones with metastatic defects have been measured in vitro, and depend on defect geometry, bone properties, and the type of loadin g, For a diaphyseal defect that destroys 50% of the cortex, strength r eductions of between 60% and 90% can occur. The load-bearing capacity of a long bone with a diaphyseal defect also can be predicted using co mputer models if the geometry of the defect and properties of surround ing bone are known. Similarly, new methods that apply basic engineerin g principles to computed tomography data allow prediction of the load- bearing capacity of vertebrae with simulated defects. By contrast, the data presented here suggest that by using plane radiographs or comput ed tomographic (CT) examinations, experienced orthopaedic surgeons can not accurately estimate the strength reductions or load-bearing capaci ty for proximal femurs with intertrochanteric defects, By combining ne w methods to predict the load-bearing capacity with estimated loads fo r activities of daily living, it is possible to calculate a factor of risk for pathologic fractures.