Effects of alendronate on lumbar posterolateral fusion using hydroxyapatite in rabbits

There are controversies regarding the effect of alendronate on spine fusion. In order to study the effects of alendronate on fusion with porous hydroxyapatite, a total of 47 rabbits underwent posterolateral lumbar fusion. The rabbits received saline (control group), alendronate 0.5 mg/kg/week (low-dose group), or alendronate 1 mg/kg/week (high-dose group) per oral beginning 2 weeks before surgery. All animals were euthanized 12 weeks after surgery, and the extent of fusion was assessed by radiographs, manual palpation, computed tomography (CT) scan, mechanical testing, and histologic examination. The fusion rates by manual palpation, radiography, and CT scan were similar in all groups. There was no significant difference in pixel optic density from the CT scan. Biomechanical testing showed the tensile strength of the control group was higher than that of the treatment group including the low- and high-dose group. In histologic examination, the fusion masses of control animals were characterized by a higher predominance of well-incorporated, trabeculated bone with a prominent marrow element. The treatment group showed a higher proportion of woven bone structures and thicker bony trabeculae. There was no significant difference in the fusion rate, but the tensile strength of treatment group was significantly lower. Histologic examination showed that alendronate inhibited bone resorption and remodeling.