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Does Increased Coefficient of Friction of Highly Porous Metal Increase Initial Stability at the Acetabular Interface?
Ashton H Goldman1, Lucas C Armstrong1, John R Owen1
1Orthopaedic Research Laboratory, Department of Orthopaedic Surgery and Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, Virginia.
Background:
Highly porous metal acetabular components illustrate a decreased rate of aseptic loosening in short-term follow-up compared with previous registry data. This study compared the effect of component surface roughness at the bone-implant interface and the quality of the bone on initial pressfit stability. The null hypothesis is that a standard porous coated acetabular cup would show no difference in initial stability as compared with a highly porous acetabular cup when subjected to a bending moment. Second, would bone mineral density (BMD) be a significant variable under these test conditions.
Methods:
In a cadaveric model, acetabular cup micromotion was measured during a 1-time cantilever bending moment applied to 2 generations of pressfit acetabular components. BMD data were also obtained from the femoral necks available for associated specimen.
Results:
The mean bending moment at 150 μm was not found to be significantly different for Gription (24.6 ± 14.0 N m) cups vs Porocoat (25 ± 10.2 N m; P > .84). The peak bending moment tolerated by Gription cups (33.9 ± 20.3 N m) was not found to be significantly different from Porocoat (33.5 ± 12.2 N m; P > .92). No correlation between BMD and bending moment at 150 μm of displacement could be identified.
Conclusion:
The coefficient of friction provided by highly porous metal acetabular shells used in this study did not provide better resistance to migration under bending load when compared with a standard porous coated component.
