Finite element models for fracture prevention in patients with metastatic bone disease. A literature review

Abstract

Patients with bone metastases have an increased risk to sustain a pathological fracture as lytic metastatic lesions damage and weaken the bone. In order to prevent fractures, prophylactic treatment is advised for patients with a high fracture risk. Mechanical stabilization of the femur can be provided through femoroplasty, a minimally invasive procedure where bone cement is injected into the lesion, or through internal fixation with intra- or extramedullary implants. Clinicians face the task of determining whether or not prophylactic treatment is required and which treatment would be the most optimal. Finite element (FE) models are promising tools that could support this decision process. The aim of this paper is to provide an overview of the state-of-the-art in FE modeling for the treatment decision of metastatic bone lesions in the femur. First, we will summarize the clinical and mechanical results of femoroplasty as a prophylactic treatment method. Secondly, current FE models for fracture risk assessment of metastatic femurs will be reviewed and the remaining challenges for clinical implementation will be discussed. Thirdly, we will elaborate on the simulation of femoroplasty in FE models and discuss future opportunities. Femoroplasty has already proven to effectively relieve pain and improve functionality, but there remains uncertainty whether it provides sufficient mechanical strengthening to prevent pathological fractures. FE models could help to select appropriate candidates for whom femoroplasty provides sufficient increase in strength and to further improve the mechanical benefit by optimizing the locations for cement augmentation.

Keywords: Bone metastases; Femoroplasty; Finite element analysis; Fracture risk; Prophylactic treatment.

Fig. 1

Two examples of metastatic bone lesions in the femur: (a) a lytic lesion in the femur neck and (b) a blastic lesion in the femur shaft.

Fig. 2

Illustration of the measurement of the axial cortical involvement of a metastatic lesion.

Fig. 3

Radiograph of a femur with an artificial defect in the neck, before (a) and after (b) augmenting the lesion with bone cement injected from the lateral aspect of the greater trochanter. Reprinted from Kaneko et al. (2007) with permission from Elsevier.

Fig. 4

Illustration of the two meshing approaches: (a) voxel-based FE mesh with brick shaped elements and (b) geometry-based mesh with tetrahedral elements.

Fig. 5

Basafa's optimization approach for cement placement. A representative model demonstrates the evolution of the cement distribution, starting from a completely filled proximal femur until the optimal distribution. Reprinted from Basafa and Armand (2014) with permission from Elsevier.