IMPROVEMENT OF THE BONE-PIN INTERFACE WITH HYDROXYAPATITE COATING - AN IN-VIVO LONG-TERM EXPERIMENTAL-STUDY

The present study was designed to comparatively evaluate the bone-pin interface in a long-term unloaded experimental study in two groups of pins, uncoated and coated with hydroxyapatite. Forty pins made of stai nless steel were used. Half of the pins were plasma-sprayed with hydro xyapatite, and the other half remained uncoated. Four adult sheep were selected. Each sheep tibia was implanted with five pins. Two sheep we re euthanized 4 months after surgery and the remaining two 12 months a fter surgery. Extraction torque was higher in the hydroxyapatite-coate d pins compared with the uncoated ones at both 4 (p less than or equal to 0.0005) and 12 months (p less than or equal to 0.0005) after impla ntation. The histological patterns observed in the sheep euthanized 4 and 12 months after implantation were very similar. An extensive bony coverage of the hydroxyapatite-coated pins without any coating resorpt ion and delamination from the metallic substrate was observed. Fibrous tissue encapsulation was found in the uncoated pins. These results de monstrate that the hydroxyapatite coating significantly improved the b one-pin interface. A similar improvement of bone-pin interface rigidit y in many clinical situations is likewise possible.