title: Cortical screw pullout strength and effective shear stress in synthetic third generation composite femurs.
abstract: BACKGROUND
  The use of artificial bone analogs in biomechanical testing of orthopaedic fracture fixation devices has increased, particularly due to the recent development of commercially available femurs such as the third generation composite femur that closely reproduce the bulk mechanical behavior of human cadaveric and/or fresh whole bone. The purpose of this investigation was to measure bone screw pullout forces in composite femurs and determine whether results are comparable to cadaver data from previous literature.
  
  
  METHODS
  The pullout strengths of 3.5 and 4.5 mm standard bicortical screws inserted into synthetic third generation composite femurs were measured and compared to existing adult human cadaveric and animal data from the literature.
  
  
  RESULTS
  For 3.5 mm screws, the measured extraction shear stress in synthetic femurs (23.70-33.99 MPa) was in the range of adult human femurs and tibias (24.4-38.8 MPa). For 4.5 mm screws, the measured values in synthetic femurs (26.04-34.76 MPa) were also similar to adult human specimens (15.9-38.9 MPa). Synthetic femur results for extraction stress showed no statistically significant site-to-site effect for 3.5 and 4.5 mm screws, with one exception. Overall, the 4.5 mm screws showed statistically higher stress required for extraction than 3.5 mm screws.
  
  
  CONCLUSIONS
  The third generation composite femurs provide a satisfactory biomechanical analog to human long-bones at the screw-bone interface. However, it is not known whether these femurs perform similarly to human bone during physiological screw "toggling."
authors.affiliation: Martin Orthopaedic Biomechanics Lab, St. Michael's Hospital, Toronto, ON, Canada.
authors.forename: Radovan
authors.initials: R
authors.lastname: Zdero
authors.forename: Shaun
authors.initials: S
authors.lastname: Rose
authors.forename: Emil H
authors.initials: EH
authors.lastname: Schemitsch
authors.forename: Marcello
authors.initials: M
authors.lastname: Papini
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000592:standards*; D002102:Cadaver; D004867:Equipment Design; D005269:Femur / Q000033:anatomy & histology / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D016268:Internal Fixators / Q000592:standards*; D008422:Materials Testing; D013314:Stress, Mechanical