Factors That Influence Bone-Ingrowth Fixation of Press-Fit Acetabular Cups.

Abstract

» In order to obtain long-term osseointegration, a press-fit acetabular cup must gain initial rigid stability with limited micromotion. In addition, the implant surface must promote ingrowth and maintain contact with viable bone.» Two-dimensional (2D) ongrowth surfaces that have been plasma-spray-coated (heated titanium alloy powder that is flame-sprayed on the substrate) and blasted with grit (surface roughness 4 to 6 µm) achieve fixation via bone interlocking into irregularities in the surface of the implant. Tridimensional ingrowth surfaces, such as titanium fiber mesh (titanium fiber diffusion-bonded to the substrate) and sintered cobalt-chromium and titanium beads, yield secure fixation when bone forms in the voids of the 3-dimensional (3D) surface.» Porous metals that mimic the trabeculae of bone and have a modulus of elasticity similar to bone have higher coefficients of friction than older designs and have demonstrated excellent osteoconductive properties. Not only do these highly porous 3D ingrowth surfaces have a high coefficient of friction, they have demonstrated higher initial stability compared with 2D ongrowth surfaces and older 3D ingrowth surface designs.» Acetabular cups promote biologic fixation with various tridimensional metal surfaces. Materials including porous Trabecular Metal (Zimmer Biomet) have been proven to achieve good osseointegration in patients with poor host bone, including patients with previous radiation exposure, osteonecrosis, or metabolic bone disease, or those who are undergoing revision surgery.