聚甲基丙烯酸甲酯强化和修复椎弓根螺钉的生物力学研究

Augmentation and restoration of pedicle screw fixation with polymethylmethacrylate: an in vitro biomechanical study

目的评价聚甲基丙烯酸甲酯(polymethylmethacrylate ,PMMA)强化和修复椎弓根螺钉固定的生物力学效果。方法8具成人新鲜腰椎骨L3～5,随机选择一侧椎弓根放置直径为6.0mm的CCD(compactCD)椎弓根螺钉 ,另一侧以直径为3.5mm的钻头导孔 ,均不穿透椎体前皮质。在材料试验机上进行椎弓根螺钉拔出实验 ,拔出速率为5mm/min。然后沿椎弓根孔道注入PMMA粉和水按体积1∶2混合的PMMA强化修复材料3～5ml,双侧椎弓根分别使用与前相同的CCD椎弓根螺钉 ,室温下1h后再行前述拔出实验。沿椎弓根螺钉长度方向锯开标本 ,观察PMMA在螺钉孔道中的分布范围。结果CCD椎弓根螺钉在正常椎弓根内的最大拔出力为 (825.5±254.7)N ;在经强化后的正常椎弓根内和在修复失效的椎弓根内 ,CCD椎弓根螺钉最大拔出力分别为 (1711.1±488.8)N和 (1832.4±497.4)N ,高于正常椎弓根螺钉的最大拔出力 ,差异有显著性意义(P<0.01)。PMMA在螺钉周围的分布与其注入时的粘稠度有关 ,未见椎管内或椎弓根外有PMMA分布。结论沿椎弓根孔道注入PMMA可显著增加椎弓根螺钉的拔出力 。

Objective To evaluate pedicle screw fixation strength following augmentation and restoration with polymethylmethacrylate (PMMA). Methods Compact CD (CCD) screws of 6.0 mm diameter was implanted into the pedicle unilaterally. And a pilot hole was created using 3.5 mm drill contralaterally on eight fresh human lower lumbar vertebrae (L 3-5).Neither the screws nor the drillings penetrated the anterior cortex of the vertebral bodies. The screws were pulled out from the vertebrae at 5 mm/min. The screw track and the pilot hole were filled with 3-5 ml of PMMA. Then, the screws were implanted bilaterally, and the PMMA was allowed to harden for 1 hour. Morphology of PMMA around the screws was observed by section of the vertebrae along the screw. Results Pullout force of pedicle screw fixation in normal vertebrae was (825.5±254.7) N and (1 711.1±488.8)N following augmentation with PMMA. Restoration of a pullout pedicle screw fixation with PMMA was able to salvage pullout force to (1 832.4±497.4) N. The pullout forces following augmentation and restoration were significantly greater than that in normal vertebrae. Morphology of PMMA around the screws was related to the viscosity of PMMA during injection. No PMMA was found in vertebral canal or surface of pedicle. Conclusion Augmentation and restoration with PMMA offered a significantly increase of strength for pedicle screw fixation, and could be used clinically in case of failure of pedicle screw fixation.