The Influence of Alendronate on Spine Fusion in an Osteoporotic Animal Model

Study Design. A posterolateral lumbar fusion model in osteoporotic rats. Objective. To assess the effect of alendronate on spine fusion in an osteoporotic animal model. Summary of Background Data. The effect of alendronate on spine fusion is still controversial. Also, there are no studies using an osteoporotic animal model to assess the effect of alendronate on spine fusion. Methods. Forty-six female Sprague-Dawley rats underwent either sham-operation (sham) (N = 24) or bilateral ovariectomy (OVX) (N = 22). Eight weeks after the first surgery, animals underwent intertransverse spine fusion at L4-L5. Animals received saline or alendronate 70 mu g/kg/wk by subcutaneous administration once a week for 8 weeks after spinal arthrodesis. All animals were divided into four groups: sham-control, sham-alendronate, OVX-control, and OVX-alendronate. After that the animals were killed and the fusion mass was assessed by radiographic, peripheral quantitative computed tomography (pQCT) scanning, and biomechanical and histologic analysis. Results. In the radiographic study and the pQCT scanning, the area of fusion masses of animals treated with alendronate was considerably larger and denser than that of the control animals in both sham and OVX groups. In the biomechanical study, the ultimate load of the fusion mass of alendronate-treated animals was higher than that of control animals in the osteoporotic groups. Histologic analysis of sagittal sections of fusion mass revealed greater new bone formation in alendronate-treated animals in osteoporotic models and significant inhibition of osteoclasts among the grafted area of alendronate-treated animals compared with the control models. Conclusion. Alendronate was effective for radiologic, biomechanical, and histologic success of spine fusion in an osteoporotic animal model. Though much of the graft bone was not resorbed, alendronate increased biomechanical strength with ingrowth of new bone formation in osteoporotic animals. This study suggests the alendronate may improve spine fusion healing in the presence of osteoporosis.