Hydroxyapatite enhances long-term fixation of titanium implants

The aim of this study was to evaluate osseous integration of hydroxyapatite coated titanium implants over time as compared to pure titanium. In 20 rats the medullary cavity of both femoral bones was entered by an awl from the trochanteric area. With steel burrs it was successively reamed to a diameter of 2.0 mm. Nails with a diameter of 2.0 mm and with a length of 34 mm were inserted into the medullary cavity; a pure titanium nail on the left side and a titanium nail entirely plasma-sprayed with hydroxyapatite (HA) on the right side. The surface roughness of the pure titanium was characterized by Ra 2.6 microm and Rt 22 microm, and HA had a roughness of Ra 7.5 (arithmetical mean roughness) microm and Rt (maximum profile height) 52 microm. The rats were randomized to a follow-up of 6 and 12 months, respectively. At sacrifice the femoral bones were dissected free from soft tissues. The bones were radiographed and then immersed in fixative. A specimen-slice of about 5 mm thickness was prepared from the region under the trochanter minor with a water cooled band-saw. Sample preparation for undecalcified tissue followed the internal guidelines at the laboratories of Biomaterials/Handicap Research. At 6 months the median bone bonding contact of the implants was 40% (range 0-92) in the titanium group and 34% (0-86) in the HA group. At 12 months the median bone bonding contact was 51% (0-97) in the titanium group and 86% (72-98) in the HA group. In conclusion, we found a significant (p = 0.001) increase in bone bonding contact from 6 to 12 months of the HA coated nails and significantly (p = 0.043) enhanced bone bonding contact in HA coated nails at 12 months as compared to pure titanium nails.