Bone response to porous tantalum implants in a gap-healing model.

OBJECTIVES: The objective of this study was to determine the relative osteogenic behavior of titanium implants with or without a porous tantalum modification when placed with a gap between the implant and existing bone. MATERIALS AND METHODS: A gap-healing model in the rabbit tibia was used for placement of titanium implants. Forty-eight rabbits received 96 implants, with 48 of the implants containing a porous tantalum middle section and the remaining 48 implants were composed of solid titanium. After 4, 8, and 12 weeks of healing, biomechanical stability was measured with removal torque testing, implant-adherent cells were isolated for analysis of osteogenic gene expression, and histomorphometric analysis was performed on sections of the implants and surrounding bone. RESULTS: Increased osteogenic activity at 4 weeks was demonstrated by upregulation of key osteogenic genes at implants containing porous tantalum which was accompanied by greater bone-implant contact at 4, 8, and 12 weeks and significantly greater removal torque at 8 and 12 weeks. CONCLUSIONS: Implants containing porous tantalum demonstrated increased peri-implant bone formation within this gap-healing model as shown by significant differences in biomechanical and histomorphometric outcomes. Such implants may represent an alternative to influence bone healing in surgical sites with an existing gap.