Effect of zoledronic acid on spinal fusion outcomes in an ovariectomized rat model of osteoporosis

To evaluate the effect of zoledronic acid (ZA) on spinal fusion in ovariectomized (OVX) rats. Female SD rats (n = 50) were OVX or sham‐operated and randomized into five groups: Sham, OVX control, ZOL‐20 (20 µg/kg), ZOL‐100 (100 µg/kg), and ZOL‐500 (500 µg/kg). Eight weeks after OVX, bilateral lumbar spinal fusion was performed using autologous iliac bone with ZA or saline according to the grouping. The lumbar spines were harvested at 8 weeks and subjected to radiographic, manual palpation, micro‐computed tomographic (micro‐CT), and histological analysis. The manual palpation result differed significantly only between the ZOL‐500 (fused: partially fused: not fused, 9:0:0) and OVX control (4:2:3) (p < 0.05). The radiographic scales were also differed significantly only between these two groups. According to the micro‐CT results, the bone volume fraction (BV/TV) were significantly higher in all ZA‐treated groups (54.2%, 65.9%, and 73.6%) than OVX control (43.7%) (p < 0.01). At clinical dose or lower, ZA didn't alter the spinal fusion, but a higher dose increased the spinal fusion rate significantly. This study suggests ZA may have a positive effect on spinal fusion in the presence of osteoporosis, and spinal fusion surgery outcome is not likely to be altered by ZA at clinical dose. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1297–1304, 2015.