The effect of surface immobilized bisphosphonates on the fixation of hydroxyapatite-coated titanium implants in ovariectomized rats.

Immobilized bisphosphonates (BPs) have been introduced to improve implant fixation, however, no information could be found about the efficiency of this approach in osteoporotic bone. This study was designed to evaluate the bone response to surface immobilized BPs on implants inserted in tibiae of ovariectomized (OVX) rats. Three months after bilateral ovariectomy, 40 rats were randomly assigned into four groups for implantation of hydroxyapatite-coated titanium implants with or without immobilized BPs: (1) control group (without BP treatments); (2) pamidronate (PAM) group (1mg/ml of PAM immersing); (3) ibandronate group (1mg/ml of ibandronate immersing); and (4) zoledronic acid (ZOL) group (1mg/ml of ZOL immersing). After implantation periods of 3 months, the peri-implant-bone density, trabecular microstructure, bone-implant interface and mechanical fixation of implants were evaluated by dual energy X-ray absorptiometry, micro-computed tomography, histology and push-out test. We found that three BPs triggered pronounced bone-implant integration and early bone formation around implants in OVX rats, with a rank order of ZOL>ibandronate>PAM. These results provide new evidence that immobilized BPs have positive effects on implant fixation in osteoporotic bone, in addition to their well-documented potency to inhibit implant loosening in normal bone.