A patient-specific mechanical modeling of metastatic femurs

Computed tomography-based finite element (FE) models were widely used to assess the femur strength. In the case of metastatic femurs, the usually-adopted linearly-elastic constitutive description leads to neglect of any specific material property of metastasis, as well as the biomechanical interaction between the lesion and the surrounding tissue. Experimental evidence showed that the metastatic tissue is characterized by a porous solid matrix with interstitial fluids, that induces mechanical alterations in the bone adjacent to the metastasis. Such an aspect is fundamental for describing growth and remodelling processes. As such, a refinement of local constitutive description for the metastasis could be necessary to obtain a comprehensive understanding of femoral mechanical behavior and to identify failure scenarios, as well as to detect localized effects. In this work, a clinical case related to a patient with both femurs affected by multiple metastases is numerically analyzed. Healthy bone tissue and metastases were described by a linearly poroelastic approach. The bone-metastasis interaction was modelled through a Gaussian-shaped graded transition of material properties in the bone around the metastasis. A progressive damage procedure was implemented by a displacement-driven incremental approach and considering a strain-based failure criterion. The results showed that the proposed approach impact the macro-scale femoral mechanical response in terms of femur strength and damage patterns, highlighting local strain accumulations connected to the lesion evolution. The proposed strategy may improve the femur strength prediction, allowing the development of an accurate fracture risk indicator for metastatic femurs to be used in clinical practice.