Predicting the stiffness and strength of human femurs with real metastatic tumors

Zohar Yosibash; Romina Plitman Mayo; Gal Dahan; Nir Trabelsi; Gail Amir; Charles Milgrom

doi:10.1016/j.bone.2014.09.022

Predicting the stiffness and strength of human femurs with real metastatic tumors

Bone. 2014 Dec:69:180-90. doi: 10.1016/j.bone.2014.09.022. Epub 2014 Oct 2.

Authors

Zohar Yosibash¹, Romina Plitman Mayo², Gal Dahan², Nir Trabelsi³, Gail Amir⁴, Charles Milgrom⁵

Affiliations

¹ Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel. Electronic address: zohary@bgu.ac.il.
² Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
³ Department of Mechanical Engineering, Shamoon College of Engineering, Beer-Sheva, Israel.
⁴ Department of Pathology, Hadassah University Hospital, Jerusalem, Israel.
⁵ Department of Orthopaedics, Hadassah University Hospital, Jerusalem, Israel.

PMID: 25284156
DOI: 10.1016/j.bone.2014.09.022

Abstract

Background: Predicting patient specific risk of fracture in femurs with metastatic tumors and the need for surgical intervention are of major clinical importance. Recent patient-specific high-order finite element methods (p-FEMs) based on CT-scans demonstrated accurate results for healthy femurs, so that their application to metastatic affected femurs is considered herein.

Methods: Radiographs of fresh frozen proximal femur specimens from donors that died of cancer were examined, and seven pairs with metastatic tumor were identified. These were CT-scanned, instrumented by strain-gauges and loaded in stance position at three inclination angles. Finally the femurs were loaded until fracture that usually occurred at the neck. Histopathology was performed to determine whether metastatic tumors are present at fractured surfaces. Following each experiment p-FE models were created based on the CT-scans mimicking the mechanical experiments. The predicted displacements, strains and yield loads were compared to experimental observations.

Results: The predicted strains and displacements showed an excellent agreement with the experimental observations with a linear regression slope of 0.95 and a coefficient of regression R(2)=0.967. A good correlation was obtained between the predicted yield load and the experimental observed yield, with a linear regression slope of 0.80 and a coefficient of regression R(2)=0.78.

Discussion: CT-based patient-specific p-FE models of femurs with real metastatic tumors were demonstrated to predict the mechanical response very well. A simplified yield criterion based on the computation of principal strains was also demonstrated to predict the yield force in most of the cases, especially for femurs that failed at small loads. In view of the limited capabilities to predict risk of fracture in femurs with metastatic tumors used nowadays, the p-FE methodology validated herein may be very valuable in making clinical decisions.

Keywords: Femur; Metastatic tumors; p-FEMs.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Aged
Bone Neoplasms / physiopathology*
Bone Neoplasms / secondary*
Female
Femur
Finite Element Analysis
Fractures, Bone / etiology
Fractures, Bone / physiopathology
Humans
Male
Middle Aged
Risk Factors
Stress, Mechanical