The Influence of Alendronate Treatment and Bone Graft Volume on Posterior Lateral Spine Fusion in a Porcine Model

Abstract

An experimental animal study with randomized, paired control design was conducted using a porcine model. The aim of this study was to evaluate the influence of alendronate treatment and the significance of different amounts of bone graft on posterior lateral spine fusion. Treatment with bisphosphonates inhibits osteoclast-induced bone resorption and increases bone quality and density. It has been widely used clinically for treatment of osteoporosis. Bisphosphonates have been reported to elongate the callus remodeling process during fracture healing. Bisphosphonate treatment may modify bone graft healing and the remodeling process in spine fusion. The bone resorption phase exists during the healing process. Extensive bone graft resorption could reduce the basis for new bone formation, which could be an important factor for failure of spine fusion. Furthermore, different amounts of initially applied bone graft may influence spine fusion rate and bone graft incorporation process. Twenty-two pigs were included in the study. Eleven pigs in the treatment group received alendronate 10 mg/day p.o. for 3 months after surgery. The other 11 pigs received no bisphosphonate and served as control group. Posterior lateral fusion with the CD Horizon system was performed on the lumbar spine using different amounts of autograft (4 g on one side and 8 g on the other side) in all animals. The fusion was evaluated using radiograph, CT scan, and histomorphometry at 3 months after operation. There was no statistical difference in either fusion rate or fusion mass volume between the two groups. The fusion rate based on radiograph was 75% on the 8-g autograft side and 45% on the 4-g side (P < 0.05). The mean volume of fusion mass was 2.36 cm3 on the 4-g side and 3.29 cm3 on the 8-g side (P < 0.01). No difference was found in either trabecular bone volume or fusion rate between treatment and control groups using histologic evaluation.The treatment group showed a higher fibrous tissue volume(P < 0.05), higher proportion of woven bone structure(P < 0.001), and lower bone marrow volume (P = 0.088) in the fusion mass. Different amounts of bone graft did not change the tissue composition of the fusion mass. Alendronate treatment in this study decreased fusion mass remodeling without inhibiting fusion rate. Increased amounts of autologous bone graft could improve the fusion rate in this experimental spine fusion study.