Background: The anti-osteoporotic drug raloxifene reduces the risk of vertebral fractures by increasing bone mass density. We investigated whether raloxifene offers any benefits in augmenting early fixation of orthopedic implants in the setting of impaction bone grafting. Methods: 24 non-weight-bearing grafted gap implants were inserted bilaterally into the tibia of 12 dogs. The 2.5-mm periimplant gap was filled with either raloxifene-impregnated or untreated bone allograft. Implants were harvested after 28 days. Implant fixation was assessed by mechanical testing and histomorphometric evaluation. Results: Raloxifene-treated allograft reduced early implant fixation compared to untreated allograft, as measured by inferior maximum shear strength (p < 0.001) and apparent shear stiffness (p = 0.001). We found that the raloxifene group had more newly formed bone in the gap around the implant (p = 0.02), but also less allograft (p = 0.03). Interpretation: The accelerated allograft resorption in the raloxifene group explained the impaired early fixation, despite its stimulation of new bone formation. Our results with local and possible high-dose treatment are not consistent with current theory regarding the mechanism of how systemic raloxifene administration counteracts the decrease in BMD in postmenopausal women. Instead of being solely anti-resorptive as generally held, our results indicate a possible anabolic side of raloxifene.
Bibliographical noteFunding Information:
We thank laboratory technician Jane Pauli for invaluable assistance during preparation of specimens for mechanical and histological evaluation. We also thank Professor Karl Anker Jørgensen and Dr Hao Jiang of the Department of Chemistry at Aarhus University for help with NMR stability testing. The project was supported unconditionally by the Orthopaedic Research Fund of Aarhus University Hospital, the Institute of Clinical Medicine at Aarhus University, the Danish Rheumatism Association, and the Housing Cooperatives Humanitarian and Cultural Fund, Agriculture and Food, Denmark. The project was also partly supported by NIH grant AR-42051. Implant coating was provided unconditionally by DePuy Inc., Warsaw, IN.
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