Patient-specific finite element computer models improve fracture risk assessments in cancer patients with femoral bone metastases compared to clinical guidelines.

Nico Verdonschot,Yvette Van Der Linden,Paulien Westhoff,Onarisa Ayu,Gerco Van Der Wal,Marianne De Jong,Loes Derikx,Arjonne Laar,Herman M Kroon,Esther Tanck,Tom Rozema,Florieke Eggermont,Sander Dijkstra

doi:10.1016/j.bone.2019.115101

Abstract

To determine whether patient-specific finite element (FE) computer models are better at assessing fracture risk for femoral bone metastases compared to clinical assessments based on axial cortical involvement on conventional radiographs, as described in current clinical guidelines. Forty-five patients with 50 femoral bone metastases, who were treated with palliative radiotherapy for pain, were included (64% single fraction (8Gy), 36% multiple fractions (5 or 6x4Gy)) and were followed for six months to determine whether they developed a pathological femoral fracture. All plain radiographs available within a two month period prior to radiotherapy were obtained. Patient-specific FE models were constructed based on the geometry and bone density obtained from the baseline quantitative CT scans used for radiotherapy planning. Femoral failure loads normalized for body weight (BW) were calculated. Patients with a failure load of 7.5 x BW or lower were identified as having high fracture risk, whereas patients with a failure load higher than 7.5 x BW were classified as low fracture risk. Experienced assessors measured axial cortical involvement on conventional radiographs. Following clinical guidelines, patients with lesions larger than 30mm were identified as having a high fracture risk. FE predictions were compared to clinical assessments by means of diagnostic accuracy values (sensitivity, specificity and positive (PPV) and negative predictive values (NPV)). Seven femurs (14%) fractured during follow-up. Median time to fracture was 8 weeks. FE models were better at assessing fracture risk in comparison to axial cortical involvement (sensitivity 100% vs. 86%, specificity 74% vs. 42%, PPV 39% vs. 19%, and NPV 100% vs. 95%, for the FE computer model vs. axial cortical involvement, respectively). Patient-specific FE computer models improve fracture risk assessments of femoral bone metastases in advanced cancer patients compared to clinical assessments based on axial cortical involvement, which is currently used in clinical guidelines.

Highlights

Patients with bone metastases carry a risk of pathological fractures. [1,2,3] If a pathological fracture occurs in a weight-bearing bone such as the femur, this leads to an immediate decrease in the patient’s mobility and self-care, and as a result in a reduced quality of life and possibly shortened survival [4,5]
A patient-specific finite element (FE) computer model based on quantitative CT scans (QCT) is a promising tool for fracture risk assessment. [14,15,16,17,18,19,20] In a recent cohort study [21], we showed that the fracture risk assessments of the FE models were superior to those of experienced clinicians that assessed fracture risk in a test set-up on digitally reconstructed radiographs (DRRs)
FE models were better at assessing fracture risk in comparison to the clinical guidelines: the fracture risk of more femurs, either high or low, was correctly assessed

Summary

Introduction

Patients with bone metastases carry a risk of pathological fractures. [1,2,3] If a pathological fracture occurs in a weight-bearing bone such as the femur, this leads to an immediate decrease in the patient’s mobility and self-care, and as a result in a reduced quality of life and possibly shortened survival [4,5]. Bone 130 (2020) 115101 fracture risk are treated with radiotherapy, usually a single fraction (SF) of 8 Gy, to relieve pain, whereas patients with an expected high fracture risk are considered firstly for preventive stabilizing surgery. In case of an expected high fracture risk, but the patient refuses surgery, radiotherapy in multiple fractions (MF) will be given, with the goal to prevent a pathological fracture by inducing remineralization [6,7,8]. Mirels et al.[11] developed a scoring system that is widely used for fracture risk assessment. This score combines ratings of pain, lesion type, size and location, and runs from 4 to 12. Patients who would never have developed a fracture during their remaining lifetime undergo surgery [7]

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