Department of Orthopaedic Surgery, Spine Section, Bone and Joint Research Center, Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Taoyuan, Taiwan.
Graduate Institute of Biomedical Engineering, Chang Gung University, 33302, Taoyuan, Taiwan.
Sci Rep. 2022 Feb 17;12(1):2739. doi: 10.1038/s41598-022-06724-4.
Polymethylmethacrylate (PMMA) has been applied clinically and biomechanically repair loose pedicle screws. Controversies have arisen over data due to uncontrolled cement properties, various locations and sizes of fenestrated holes in repair screws, irregular holes and different bone densities of specimens. In this study, the pullout strength was compared for two techniques, the modified technique to use PMMA to augment a threaded hole and the traditional technique with retrograde injection of a PMMA filling, for standard loose screws in porcine vertebrae. Both techniques provided statistically significant results for sufficiently randomized specimens and experimental procedures. The difference in the pullout strength between conical and cylindrical screws for the aforementioned cement augmentation techniques was also investigated. Twenty-four single-level fresh-frozen lumbar vertebrae from L1 to L6 were harvested from four mature pigs. A total of 0.8 ml of PMMA was retrograde injected into screw holes with a 5.5 mm diameter, followed by insertion of a 5.0 mm diameter repair screw in the traditional group (n = 12). A stiff threaded PMMA hole was created with a 4.5 mm tapping screw before insertion of repair screws in the modified group (n = 12). Two screw geometries were randomly assigned as cylindrical (n = 6) and conical (n = 6) in each group. The correlations between filling techniques, screw geometries and axial pullout strength were analyzed. An appropriate screw trajectory and insertion depth were confirmed using X-ray imaging prior to pullout testing in both groups. For a given screw geometry (cylindrical or conical), the pullout force of the modified group was significantly higher than that of the traditional group. There was no significant difference in the pullout force between the screw geometries for a given filling technique. The cement augmentation technique is far more influential than the screw outer geometry. The modified PMMA technique created a greater anchor force than the traditional method and could be an alternative for revision of pedicle screw loosening.
聚甲基丙烯酸甲酯（PMMA）已在临床上和生物力学上应用于修复松动的椎弓根螺钉。由于未控制的水泥特性、修复螺钉上各种位置和大小的开窗孔、不规则孔和不同骨密度的标本，导致数据存在争议。在这项研究中，比较了两种技术的拔出强度，一种是改良技术，使用 PMMA 增强螺纹孔，另一种是传统技术，将 PMMA 填充物逆行注射到螺纹孔中，用于猪椎骨中的标准松动螺钉。对于足够随机的标本和实验程序，这两种技术都提供了统计学上显著的结果。还研究了上述水泥增强技术中锥形和圆柱形螺钉之间拔出强度的差异。从四只成熟猪中取出 L1 到 L6 的 24 个单节段新鲜冷冻腰椎。在传统组（n=12）中，用 5.5mm 直径的螺钉将 0.8ml 的 PMMA 逆行注射到直径为 5.5mm 的螺钉孔中，然后插入 5.0mm 直径的修复螺钉。在改良组（n=12）中，先用 4.5mm 的攻丝螺钉创建一个刚性螺纹 PMMA 孔，然后插入修复螺钉。在每组中，随机分配两种螺钉几何形状为圆柱形（n=6）和锥形（n=6）。分析了填充技术、螺钉几何形状和轴向拔出强度之间的相关性。在两组中，在拔出测试之前，使用 X 射线成像确认了适当的螺钉轨迹和插入深度。对于给定的螺钉几何形状（圆柱形或锥形），改良组的拔出力明显高于传统组。对于给定的填充技术，螺钉几何形状的拔出力没有显著差异。水泥增强技术的影响远远大于螺钉的外几何形状。改良的 PMMA 技术比传统方法产生更大的锚固力，可能是修复椎弓根螺钉松动的替代方法。
