Quantification of bone ingrowth within bone-derived porous hydroxyapatite implants of varying density

Hydroxyapatite has been investigated for use in the osseous environment for over 20 years and the biocompatibility of the ceramic and its osseoconduct ive behavior is well established. Therefore, the use of porous hydroxyapati te for the repair of osseous defects seems promising with potential for com plete penetration of osseous tissue and restoration of vascularity througho ut the repair site. However, there have been few systematic studies of the effects of physical properties such as macropore size and pore connectivity on the rate and quality of bone integration within porous hydroxyapatite i mplants. This paper quantifies the early biological response to a well-char acterized series of implants with uniform microstructure and phase composit ion, but differing macrostructures and demonstrates the dependence of the r ate of osseointegration on the apparent density of porous hydroxyapatite as a function of pore connectivity. Furthermore, compression testing establis hed that bony ingrowth has a strong reinforcing effect on porous hydroxyapa tite implants, which is more pronounced in the lower density implants, as a result of a greater relative volume of bone ingrowth. (C) 1999 Kluwer Acad emic Publishers.