An animal model for interface tissue formation in cemented hip replacements.
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.
El-Warrak
Alexander O
AO
Musculoskeletal Research Unit, Department of Veterinary Surgery, University of Zurich, Zurich, Switzerland. warrakel@uiuc.edu
Olmstead
Marvin
M
Apelt
Detlef
D
Deiss
Felix
F
Noetzli
Hubert
H
Zlinsky
Kathy
K
Hilbe
Monika
M
Bertschar-Wolfsberger
Regula
R
Johnson
Ann L
AL
Auer
Joerg
J
von Rechenberg
Brigitte
B
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
D001843:Bone Cements