| Objective To compare the stability of injectable pedicle screw with different volumes and distributions of polymethylmethacrylate (PMMA) in severely osteoporotic (OP) synthetic bone and analyze the relationship between screw stability and volume and distribution of PMMA. Methods Severely OP synthetic bone were randomly divided into group A, B, C, D with different kinds of screws, and then blocks in each group were randomly divided into subgroups 0, 1, 2, 3 with different volumes of PMMA. A pilot hole was prepared in advance using the same method in all samples. Pedicle screws of type A-C were directly inserted into vertebrae in groups A-C respectively, and then different volumes of PMMA (0, 2.0, 2.5, 3.0 mL) were injected through screw into blocks in subgroups 0, 1, 2, 3 respectively. The pilot hole was filled with different volumes of PMMA (0, 2.0, 2.5, 3.0 mL) followed by insertion of screw in groups D0, D1, D2 and D3 respectively. X-ray examination was performed to evaluate the distribution of PMMA, and axial pull-out test was performed to measure the maximum axial pullout strength (Fmax). Results X-ray examination revealed PMMA surrounding the anterior 1/3 part of screw in groups A1-A3, surrounding the middle 1/3 part of screw in groups B1-B3 and groups C1-C3, and surrounding the full length of screw evenly in groups D1-D3. Two factors like volume and distribution of PMMA showed significant influence on Fmax(P<0.05), and there was no significantly correlated influence between volume and distribution of PMMA (P>0.05). Among groups with the same screw, there were no significant differences in Fmax between groups with injection of 2.0 mL and 2.5 mL PMMA and between groups with injection of 2.5 mL and 3.0 mL PMMA (P>0.05). Fmax in groups with injection of 3.0 mL PMMA was significantly higher than that in groups with injection of 2.0 mL PMMA (P<0.05). Fmax in group A1 was significantly lower than that in group D1 (P<0.05), and there were no significant differences between other two groups with the same volume of PMMA (P>0.05). Conclusion PMMA can significantly enhance the stability of different injectable pedicle screws in severely OP synthetic bone, and the volume and distribution of PMMA significantly influence the screw stability. Injection of 3.0 mL PMMA through injectable screw with 180°-four lateral holes in group A or injectable screw with 180°-six lateral holes in group B is considered the preferred choice in severely OP synthetic bone. |
