title: Predicting the stiffness and strength of human femurs with real metastatic tumors.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel. Electronic address: zohary@bgu.ac.il.
authors.forename: Zohar
authors.initials: Z
authors.lastname: Yosibash
authors.affiliation: Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
authors.forename: Romina
authors.initials: R
authors.lastname: Plitman Mayo
authors.affiliation: Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
authors.forename: Gal
authors.initials: G
authors.lastname: Dahan
authors.affiliation: Department of Mechanical Engineering, Shamoon College of Engineering, Beer-Sheva, Israel.
authors.forename: Nir
authors.initials: N
authors.lastname: Trabelsi
authors.affiliation: Department of Pathology, Hadassah University Hospital, Jerusalem, Israel.
authors.forename: Gail
authors.initials: G
authors.lastname: Amir
authors.affiliation: Department of Orthopaedics, Hadassah University Hospital, Jerusalem, Israel.
authors.forename: Charles
authors.initials: C
authors.lastname: Milgrom
mesh_terms: D000368:Aged; D001859:Bone Neoplasms / Q000503:physiopathology* / Q000556:secondary*; D005260:Female; D005269:Femur; D020342:Finite Element Analysis; D050723:Fractures, Bone / Q000209:etiology / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013314:Stress, Mechanical
keywords: Femur; Metastatic tumors; p-FEMs