MECHANICAL AND HISTOLOGICAL FIXATION OF HYDROXYLAPATITE-COATED PYROLYTIC CARBON AND TITANIUM-ALLOY IMPLANTS - A REPORT OF SHORT-TERM RESULTS

Historically, pyrolytic carbon has been a material for cardiovascular applications, but it has several properties suited for orthopedic uses as well. Pyrolytic carbon has an elastic modulus similar to bone and is highly fatigue resistant, but has not been used in orthopedics beca use of poor fixation to bone. Plasma sprayed hydroxylapatite (HA) has significantly improved the bonding of bone to titanium alloy implants. The effect of plasma-sprayed HA on pyrolytic carbon implants was inve stigated in this study. Cylindrical samples were implanted through a s ingle cortex in Beagle femurs. The animals were sacrificed after 8 wee ks, and a mechanical push-out test was performed on the implants immed iately after explantation. Samples were microradiographed, stained for histology, and examined histomorphometrically. Interface strength for each type of implant was calculated. Pyrolytic carbon showed almost n o attachment strength with an average strength value of 1.59 MPa. HA-c oated pyrolytic carbon (8.71 MPa) yielded the same interfacial strengt h as HA-coated titanium (8.71 MPa). Histology revealed that bone was i n direct apposition to all implants, both HA coated and noncoated. Fai lures occurred between the core material and the coating, or within th e coating, but not at the bone/HA interface. Histomorphometry results confirmed that the two types of HA-coated implants had more bone appos ition than the uncoated pyrolytic carbon implants. It was concluded th at a plasma sprayed HA coating significantly improves the bone fixatio n of pyrolytic carbon. (C) 1995 John Wiley & Sons, Inc.