title: Influence of cement penetration and graft density on stem stability in impaction allografting: a finite element study.
abstract: BACKGROUND
  Excessive stem migration is often problematic after impaction allografting. The mechanisms responsible for migration are not known, but achieving a dense graft bed has traditionally been believed to be essential for stem stability. When the stem is cemented into the allograft bed, however, the graft becomes infiltrated with bone cement. Extensive cement penetration into the graft has been observed in previous studies, resulting in regions of cement-endosteum contact.
  
  
  METHODS
  This study explored the effects of graft density and cement penetration on stem motion using a finite element model that was validated against experimental data.
  
  
  RESULTS
  Cement penetration has a considerable stabilizing effect on stem motion, whereas graft density is important only when there is no cement-endosteum contact. Stem migration can be attributed primarily to slippage at the endosteum and stem-cement interfaces rather than to shear failure within the graft.
  
  
  CONCLUSIONS
  Partial cement penetration to the endosteum increases the likelihood of meeting clinical requirements of early implant stability, particularly when a dense graft bed cannot be achieved.
authors.affiliation: Division of Orthopaedic Engineering Research, The University of British Columbia, 3114-910 West 10th Avenue, Vancouver, BC, Canada V5Z 4E3.
authors.forename: Carolyne
authors.initials: C
authors.lastname: Albert
authors.forename: Bassam
authors.initials: B
authors.lastname: Masri
authors.forename: Clive
authors.initials: C
authors.lastname: Duncan
authors.forename: Thomas
authors.initials: T
authors.lastname: Oxland
authors.forename: Göran
authors.initials: G
authors.lastname: Fernlund
mesh_terms: D015519:Bone Density; D002484:Cementation / Q000379:methods*; D003198:Computer Simulation; D005269:Femur / Q000737:chemistry / Q000503:physiopathology* / Q000601:surgery*; D020342:Finite Element Analysis; D006622:Hip Prosthesis; D006801:Humans; D008954:Models, Biological; D009038:Motion; D013718:Tensile Strength