A histomorphometric and biomechanical study of the effect of delayed titanium implant placement in irradiated rabbit bone

Background: The time interval from irradiation to implant surgery has been considered an impact factor for implant integration in irradiated bone and the importance of a long interval between the radiation trauma and reconstructive bone surgery has been suggested. Purpose: The present study was undertaken to histomorphometrically and biomechanically analyze the effect of delayed implant placement on bone healing around titanium implants in irradiated bone. Materials and Methods: Rabbits were given a single dose of 15 Gy Cobalt⁶⁰ radiation to one hind leg, the other hind leg serving as a control. Titanium screws were inserted into the femur and tibia directly and at 12 weeks and 52 weeks after irradiation. The implants were evaluated after a healing time of 8 weeks. The torques necessary for removal of the implants were measured. Histomorphometry with respect to bone‐metal contact and amount of bone surrounding the implants was performed. Results: The biomechanical force necessary to unscrew the titanium implants in the irradiated bone was significantly increased after a resting period of 1 year between irradiation and implant placement, compared to direct implant placement. The histornorphometric evaluation showed an improvement of bone healing around the implants in the irradiated bone, both after a resting period of 12 weeks and after 1 year compared to direct implant placement. Conclusions: It is concluded that a relatively long interval between irradiation and reconstructive bone surgery will improve osseointegration of titanium implants in irradiated rabbit bone.