Augmentation of Pedicle Screw Stability With Calcium Sulfate Cement in Osteoporotic Sheep Biomechanical and Screw-bone Interfacial Evaluation

Study Design: Augmentation of pedicle screws with calcium sulfate cement (CSC) was performed in osteoporotic sheep. Biomechanical tests, micro-computed tomography (CT) analysis, and histological observation were performed. Objective: To investigate the long-term biomechanical performance of pedicle screws augmented with CSC in vivo and evaluated the screw-bone interfacial bonding with micro-CT and histological techniques. Summary of Background Data: There is little information on the long-term biomechanical performance and screw-bone interfacial bonding of pedicle screws augmented with CSC in osteoporosis in vivo. Methods: Twelve months after ovariectomy, bilateral pedicles of lumbar vertebrae (L1 to L5) of 6 female sheep were fixed with pedicle screws. One pedicle of each vertebral body was treated with a screw augmented with CSC (CSC group) and the contralateral pedicle was treated with a screw without any augmentation (control group). Three months later, the sheep were killed and biomechanical tests, micro-CT analysis, and histological observation were conducted on the isolated specimen vertebrae. Results: Twelve months after ovariectomy, animal model of osteoporosis was established successfully. Both the axial and vertical stabilities of the pedicle screws in CSC group were significantly enhanced compared with those in the control group (P < 0.05). Micro-CT reconstruction and analysis showed that there were more bone trabeculae around the screws in CSC group compared with those in control group (P < 0.05), and the bone trabeculae were significantly denser than those in control group (P < 0.05). Histological observation showed that CSC was completely degradated and bone trabeculae around the screws in CSC group were more and denser than that in the control group. Bone trabeculae held the screws tightly without any interspaces between screw and bone, which formed strong bonding between bone and screw. Conclusions: CSC can significantly improve screw-bone interfacial bonding and strengthen the long-term stability of pedicle screws in osteoporotic sheep. Augmentation with CSC may be a potentially useful method to increase the stability of pedicle screws in patients with osteoporosis.