In Vivo Study of Pedicle Screw Augmentation Using Bioactive Glass in Osteoporosis Sheep

Abstract

STUDY DESIGN: Augmentation of pedicle screws with bioactive glass (BG) was performed in osteoporotic ovine spine in vivo. Biomechanical tests, micro-computed tomography (CT) analysis, and histologic observation were performed. OBJECTIVE: To investigate the biomechanical stability of pedicle screws augmented by BG in osteoporotic sheep and observe the bone-screw interface histologically. SUMMARY OF BACKGROUND DATA: There is little information on the long-term biomechanical performance and screw-bone interfacial bonding of pedicle screws augmented with BG in osteoporotic spine in vivo. METHODS: Twelve months after ovariectomy combined with methylprednisolone injection, 8 adult female sheep were randomly divided into 2 groups (3- and 6-mo time point groups). In each time point group, pedicles were randomly selected from the lumbar spine (L1-L6) and implanted with (1) pedicle screw alone; (2) pedicle screw augmented by polymethylmethacrylate; or (3) pedicle screw augmented by BG. Three and 6 months after implantation, animals were labeled with tetracycline and calcein before being killed. Then vertebrae with pedicle screws were obtained, and a micro-CT scan, histologic analysis, and biomechanical tests were performed. RESULTS: Three months after implantation, micro-CT reconstruction showed that microstructural parameters of the BG group were significantly better compared with those in the other 2 groups (P<0.05). Histologic observation revealed that bone trabeculae around the screws in the BG group were more in number and denser than those in the control group. The average mineral apposition rate of the bone in the BG group was also higher than that in the other 2 groups (P<0.05). The mechanical properties in the BG group were also significantly higher than that in the control group. Six months after implantation, similar results except mineral apposition rate can be obtained among different groups. CONCLUSIONS: BG can significantly improve bone microstructure of the interface in osteoporosis condition and increase the hold strength of the pedicle screw.