Effects of ingrowth, geometry, and material on stress transfer under porous-coated hip surface replacements.

Three different interface geometries for porous ingrowth surface replacements of the hip were examined using two-dimensional linear and nonlinear contact finite element analyses. The results indicate that incorporation of a nearly flat prosthesis interface between the surface replacement and the underlying cancellous bone may reduce stress shielding and improve stress transfer from the component. For all designs analyzed, the bone stress shielding was insensitive to component material stiffness when the elastic modulus was greater than 30 MPa. The use of titanium instead of cobalt-chrome (Co--Cr) as the prosthesis material therefore had a negligible effect on stress shielding.