Biomechanical model of a high risk impending pathologic fracture of the femur: lesion creation based on clinically implemented scoring systems

Abstract

Background: Multiple classifications combine objective and subjective measures to predict fracture risk through a metastatic lesion. In our literature review, no studies have attempted to validate this predicted fracture risk from a biomechanical perspective. The study goal was to evaluate proximal femur strength after creating osteolytic defects. We report a standardized technique to re-create a metastatic lesion.

Methods: Eight femoral matched pairs were procured and a standardized technique was used to create an osteolytic femoral neck defect in one femur with the contralateral specimen serving as the control. Femurs were loaded to failure in a material testing machine at 2 mm/s. Failure load (N) and location of failure were documented. 3D finite element (FE) femur models with and without the lesions were developed to predict von Mises stresses in the femoral neck and compare between the two models.

Findings: Femurs containing the osteolytic defect failed at significantly lower loads than the intact specimens in a reproducible manner (intact: 10.69 kN (3.09 SD); lesion: 5.56 kN (2.03 SD), p<0.001). The average reduction in failure load was 48%, and the fracture pattern was consistent in all specimens. FE model comparison similarly predicted significantly higher von Mises stress at the lesion.

Interpretation: Our methods and pathologic fracture model represent the clinical parameters of metastatic bone disease and suggest a significant reduction in structural integrity of the lesion-containing femur. Prophylactic surgical fixation may be warranted clinically to reduce the risk of pathologic fracture. Our model technique is reproducible and may be used in future studies.