Predicting pathologic fracture risk in the management of metastatic bone defects.

Guideliues 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 counter to engi­neering practice, and do not accurately pre­dict the risk of fracture for many patients. To serve as a basis for improved guidelines, 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 ofload­ing. For a diaphyseal defect that destroys 50% of the cortex, strength reductions of be­tween 60% and 90% can occur. The load­bearing capacity of a long bone with a diaphy­seal defect also can be predicted using com­puter models if the geometry of the defect and properties of surrounding bone are known. Similarly, new methods that apply basic engi­neering principles to computed tomography data allow prediction of the load-bearing ca-