Effect on pedicle screw stability of polymethylmethacrylate volume and distribution in synthetic bone block for patients with osteoporosis / 解放军医学杂志

ABSTRACT

Objective To compare the stability of injectable pedicle screw with different lateral holes augmented with different volume of polymethylmethacrylate (PMMA) in synthetic bone block used for patients with osteoporosis,and analyze the relationship between screw stability and injected volume and distribution pattern of PMMA.Methods The synthetic bone blocks used for patients with osteoporosis were randomly divided into groups A,B,C and D according to the screw difference,and the blocks in each group were then randomly divided again into subgroups 0,1,2 and 3 according to the difference of PMMA volume.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 of groups A-C respectively,and then different volumes of PMMA (0,1.0,1.5 and 2.0ml) were injected through screw into the blocks of subgroups 0,1,2 and 3 respectively.The pilot hole was filled with different volumes of PMMA (0,1.0,1.5 and 2.0ml) followed by insertion of screw in groups D0,D1,D2 and D3 respectively.X-ray examination was performed to evaluate the screw position and PMMA distribution,and axial pull-out test was performed to measure the maximum axial pullout strength (Fmax).Results X-ray examination revealed that PMMA wrapt the anterior 1/3 part of screw in groups A1-A3,wrapt the middle 1/3 part of screw in groups B1-B3 and groups C1-C3,and evenly wrapt the full length of screw in groups D1-D3.Two factor ANOVA showed that both volume and distribution of PMMA significantly influenced Fmax (P＜0.05),but no marked interaction existed between the two factors (P=0.877).Among groups with the same screw,no significant difference of Fmax was found between the groups injected of 1.0ml and 1.5ml PMMA and those of 1.5ml and 2.0ml PMMA (P＞0.05),but the Fmax was significantly higher in groups with injection of 2.0ml PMMA than that in groups with injection of 1.0ml PMMA (P＜0.05).Among the groups injected with same volume of PMMA,no significant differences on Fmax were found among the groups A0-D0,A2-D2 and A3-D3 (P＞0.05).The Fmax was significantly lower in group A1 than in group DI (P=0.026),and no significant differences existed between the other two groups injected with the same volume of PMMA (P＞0.05).Conclusion PMMA can significantly enhance the stability of different injectable pedicle screws in synthetic bone block used for patients with osteoporosis,and the stability is significantly correlated with injected volume and distribution pattern of PMMA.