In vivo characterization of hydroxylapatite (HA) coated pyrolytic carbon implants

Low-temperature isotropic (LTI) pyrolytic carbon implants (Carbon Implants, Austin, TX) with smooth and grooved surfaces were evaluated using the canine transcortical plug model. The implants were evaluated with and without a 50-75 μm hydroxylapatite (HA) coating (Bio-Interfaces, Inc., San Diego, CA). Four adult mongrel dogs were used each receiving five transcortical implants bilaterally in the femur. The implants were evaluated mechanically and histologically at periods of 3, 4, and 6 weeks postoperatively. Mechanical pushout testing was performed to determine interface attachment strength and stiffness. Histologic sections were evaluated for interface tissue characterization, percent bone apposition, and mode of interface pushout failure. Statistical analysis revealed that RA coating significantly increased interface shear strength and stiffness of smooth pyrolytic carbon implants. A grooved surface texture resulted in improved mechanical attachment strength compared to smooth surface texture and was unaffected by the application of HA coating. Histologic evaluation showed a significant amount of direct implant-bone apposition with little or no fibrous tissue present. HA-coated implants had a significantly greater amount of direct bone apposition with both smooth and textured surfaces compared to uncoated implants