BONE RESPONSE TO DIFFERENT HYDROXYAPATITE COATED SUBSTRATES

Abstract

Osseointegration has been shown to be directly affected by surface roughness and bioactive coatings. This report compares bone response to hydroxyapatite coatings on differing substrate treatments.

Titanium cylinders was implanted bilaterally in the distal femora of 30 rabbits. One of three surface treatments was applied to each implant: plasma sprayed titanium surface without hydroxyapatite coating (P), plasma sprayed titanium surface with hydroxyapatite coating (PHA), and acid-etched surface with hydroxyapatite coating (CHA). Osseointegration was measured at 6 and 12 weeks, by histomorphometry of scanning electron microscopy images of histologic sections taken through the implant at three levels: diaphysis, metaphysis, and intermediate. Bone growth was measured up to 3 mm from the edge of the implant to determine changes in patterns of bone growth.

Overall, bone response was greatest in the diaphyseal sections. Mean osseointegration was significantly different between hydroxyapatite coated and non-hydroxyapatite coated implants (CHA: 74+10%, PHA: 65+12%, and P: 39+10%, p< 0.01). Both hydroxyapatite coated implants demonstrated increased bone growth closer to the implant which dropped off with increasing distance from the implant. Lower and relatively unchanging levels of bone growth were seen in non-hydroxyapatite coated implants.

Osseointegration and bone growth was higher in both hydroxyapatite coated surfaces confirming previous reports. The differences in substrates (acid etched vs. plasma sprayed titanium) did not yield a significant difference in bone growth, suggesting that the hydroxyapatite coating provided a much larger benefit. This study supports the hypothesis that enhanced osseointegration is primarily due to the bioactive coating.