Pathologic femoral fractures in patients with metastatic cancer are associated with high morbidity and mortality. Clinical predictions of impending fractures are inaccurate and often lead to overtreatment or underestimation. If the specific fracture risk could be assessed, patients with an impendingfracture could be saved from a traumatic event, while others with a non-impending fracture could be spared from unnecessary prophylactic treatment.
This study was aiming to investigate the effect of metastatic lesions on the biomechanical behaviour of the proximal femur. In more detail, a quantitative computed tomography (QCT)-based homogenized voxel finite element (hvFE) model was developed allowing a patient-specific pathologicfracture prediction.
First, regions in the femur, most affected by metastatic lesions, were identified by reviewing clinical data of patients, who suffered a pathologic fracture. Sixteen pairs human femora were used for data collection of the study. One femur of each pair remained intact while a defined lesion, based on clinical findings, was milled out in either the superolateral or inferomedial portion of theneck of the contralateral femur. Prior to the biomechanical experiment, the femora were scanned with QCT. All femora were loaded in a mechanical setup mimicking one-legged stance. Stiffness, ultimate load, and fracture location were evaluated. In parallel, nonlinear hvFE models were generated from QCT images of the specimens and loaded in the same way as in the experiments. Data from the experiments and simulations were compared statistically to validate the hvFE model. A first finding was that the most affected region in reviewed patients was the superolateral- and inferomedial femoral neck, causing a higher stiffness reduction in specimens with the inferomediallesion. The mean ultimate load in experiments was 40% and 75% lower for specimen with the superolateral and inferomedial lesions, respectively, compared to intact specimens. The hvFEmodel predicted both stiffness and ultimate load for tested specimens in high correlation with experimental data and with higher accuracy than clinical guidelines. In addition, the model predicted qualitatively well the failure location.
Lesions in the femoral neck lead to a reduction of structural integrity, whereby their site has a predominant effect on the magnitude of the reduction, underlining the inaccuracy of current predictive clinical guidelines. The automated subject-specific QCT-based hvFE model could predict the effectof metastatic lesions in the proximal femur better than clinical guidelines. Furthermore, it provided qualitative information about stiffness, ultimate load, and failure location in pathologic femora.