Solution deposition of hydroxyapatite on a highly porous titanium surface enhances osseointegration

Implants with a highly porous coating of Tritaniurn Dimensionalized Metal(TM) have the advantage of simulating the trabecular structure of bone to provide maximum available porous space for bone ingrowth. Plasma-sprayed hydroxyapatite coatings work well on non-porous substrates but do not coat the inner surfaces of open-porous substrates. Solution deposition can produce a consistent bioceramic coating of precise thickness on porous surfaces. This report compares bone response to a highly porous titanium surface with a solution deposited coating of hydroxyapatite. Ti6AL4V rods were implanted bilaterally in the intramedullary canals of 40 rabbit femurs. The implants had a 1.5 mm CPTi coating, which was > 65% porous with pore sizes of 250400 microns. (Tritanium Dimensionalized MetalTM). Twenty implants (T-HA) were coated with hydroxyapatite by a solution deposition method (Peri-Apatite (R)). The other 20 implants (T) had no hydroxyapatite coating. Implants were provided with a final diameter of 5 min and length of 23 mm (Howmedica Osteonics, Mahwah, NJ). Rabbit femurs were harvested at 6 and 12 weeks after surgery sectioned at two levels: in the diaphyseal and metaphyseal portion of the femoral canal. Scanning electron images (SEM) in backscattered mode were digitally captured. Osseointegration was measured by automated computerized histomorphometry of the SEM images. Mean bone ingrowth at both time points was significantly different between hydroxyapatite-coated and non-hydroxyapatite coated implants (p < 0.01). The hydroxyapatite coating had a significant benefit on the bone growth into porous titanium surfaces. Bone ingrowth was substantially higher at all time points in the hydroxyapatite-coated surface relative to the uncoated surface and in both diaphyseal and metaphyseal cross-section levels. The finding of a higher percentage of bone growth deeper in the pores of the surface is encouraging. This signifies that the solution deposited Peri-Apatite coating is capable of depositing a bioactive coat of hydroxyapatite in the depths of the porous surface. This depth of penetration is not achievable by conventional plasma-sprayed deposition of hydroxyapatite. Implants with a Tritanium Dimensionalized Metal(TM) surface and a solution deposited Peri-Apatite coating have the potential to develop into attractive alternatives for noncemented total hip arthroplasty.