X-RAY-DIFFRACTION OF BONE AT THE INTERFACE WITH HYDROXYAPATITE-COATEDVERSUS UNCOATED METAL IMPLANTS

The microstructural characteristics of the newly formed bone tissue at the interface with hydroxyapatite-coated and uncoated stain less stee l pins used in an external fracture fixation system have been evaluate d. The bone far from the interface was used as a control. Pins were tr ansversally inserted into the diaphyses of sheep tibiae and were loade d in for six weeks. Three sheep received coated pins and two received uncoated pins. Crystallographic habit and mineralization of the implan t-facing bone were evaluated. Moreover, lattice parameters of bone apa tite were measured and hydroxyapatite (HA) coating degradation was inv estigated, by means of conventional and microbeam X-ray diffraction (X RD). In coated pins, six weeks after the implantation the newly formed bone tissue at the interface did not reach complete maturation, but t he presence of the implant did not alter the apatite lattice structure ; the lattice parameters did not show statistically significant variat ions with respect to those observed in the control bone. In uncoated p ins, bone tissue rarely appeared totally mineralized and lattice param eters were significantly different with respect to those observed in t he bone far from the implant. HA particles were observed spreading in the bone-facing coated pins; the XRD pattern of bone apatite surroundi ng HA particles was unmodified. It was concluded that HA coatings impr oved the bone remodelling process during pin fixation in comparison to uncoated pins and did not alter the crystallographic habit of apatite . (C) 1998 Chapman & Hall.