title: An animal model for interface tissue formation in cemented hip replacements.
abstract: OBJECTIVE
  To create a model in sheep for investigation of early changes related to the formation of an interface membrane in hip prosthesis.
  
  
  METHODS
  Experimental study.
  
  
  METHODS
  Twenty-four female adult Swiss Alpine sheep.
  
  
  METHODS
  Sheep were divided into 2 groups of 12 for unilateral cemented total hip arthroplasty. In Group I, the prosthesis was fixed with retrograde cement gun injection to achieve a complete cement mantle, whereas in Group II a primary cement mantle defect was produced. Groups I and II were further divided into 2 sub-groups with study end points of 2 and 8.5 months after surgery. Radiographs were evaluated postoperatively and at euthanasia for migration of the femoral component and bone resorption. Histologic sections were evaluated semiquantitatively for changes in cell types and numbers, and bone reactions; and quantitatively for size of interface membrane and new bone formation.
  
  
  RESULTS
  Radiographically, there tended to be an increase in bone resorption and periosteal bone formation throughout the femoral shaft in Group II compared with Group I, but this was only statistically significant at the region of the femoral neck (R5) at both time periods (P<.05). Semiquantitative histologic evaluation revealed significant increases (P<.05) in cellularity, numbers of fibroblasts, giant cells, macrophages, and mononuclear cells, in Group II primarily at 2 months after surgery. This was also true for interface membrane formation and bone remodeling. Quantitative data showed an increased in the size of the interface membrane and area of bone formation at 8.5 months in Group II.
  
  
  CONCLUSIONS
  The cement defect model offered controlled and repeatable production of an interface membrane. The results suggest that a primary cement mantle defect could be a possible trigger for implant instability, eliciting a cascade of biomechanical and molecular events in bone tissue leading to aseptic loosening.
  
  
  CONCLUSIONS
  The results show the effect of defects in the cement mantle in promoting interface membrane formation. Long-term and biochemical studies are required to evaluate the relevance of this interface membrane formation.
authors.affiliation: Musculoskeletal Research Unit, Department of Veterinary Surgery, University of Zurich, Zurich, Switzerland. warrakel@uiuc.edu
authors.forename: Alexander O
authors.initials: AO
authors.lastname: El-Warrak
authors.forename: Marvin
authors.initials: M
authors.lastname: Olmstead
authors.forename: Detlef
authors.initials: D
authors.lastname: Apelt
authors.forename: Felix
authors.initials: F
authors.lastname: Deiss
authors.forename: Hubert
authors.initials: H
authors.lastname: Noetzli
authors.forename: Kathy
authors.initials: K
authors.lastname: Zlinsky
authors.forename: Monika
authors.initials: M
authors.lastname: Hilbe
authors.forename: Regula
authors.initials: R
authors.lastname: Bertschar-Wolfsberger
authors.forename: Ann L
authors.initials: AL
authors.lastname: Johnson
authors.forename: Joerg
authors.initials: J
authors.lastname: Auer
authors.forename: Brigitte
authors.initials: B
authors.lastname: von Rechenberg
mesh_terms: D000818:Animals; D019644:Arthroplasty, Replacement, Hip / Q000379:methods / Q000662:veterinary*; D001843:Bone Cements; D016723:Bone Remodeling; D005260:Female; D006622:Hip Prosthesis / Q000662:veterinary*; D008422:Materials Testing; D023421:Models, Animal; D011474:Prosthesis Design; D012756:Sheep
chemical_list: D001843:Bone Cements