空心侧孔椎弓根螺钉添加聚甲基丙烯酸甲酯骨水泥的生物力学研究

Biomechanical study on screws with hollow lateral holes infused with polymethylmethacrylate in pedicle of vertebral arch

目的 为改善椎弓根螺钉的稳定性 ,探讨空心侧孔椎弓根螺钉置入时添加聚甲基丙烯酸甲酯 (polymethylmethacrylate,PMMA)骨水泥强化椎弓根螺钉固定的生物力学效果。 方法 采用 8具新鲜成人尸体T11～L4 共 48个椎体 ,随机选择 32个椎体 ,其中 10个椎体一侧椎弓根放置直径 6 .5mm的空心侧孔椎弓根螺钉 ,另一侧放置实心螺钉 ,行最大轴向拔出力 (F -max)试验 (对照组 )。拔出螺钉后分别向空心和实心螺钉道注入PMMA 3～ 5ml,拧入螺钉 ,行拔出试验 (修复组 )。另选 10个椎体置入空心侧孔螺钉和实心螺钉 ,用直径 3.5mm的钻头分别导孔 ,注入PMMA和拧入螺钉 ,再行拔出试验 (强化组 ) ,并观察PMMA的分布范围。另外 12个椎体做空心侧孔椎弓根螺钉的周期抗屈试验。 10个空心侧孔螺钉和 10个实心螺钉分别做三点弯屈 (3pBend)试验。 结果 空心侧孔椎弓根螺钉对照组拔出力为 (85 5 .0± 2 0 7.5 )N ,修复组为 (192 4.4± 383.2 )N ,强化组为(1943.3± 5 35 .8)N ;实心螺钉对照组拔出力为 (82 9.2± 2 2 0 .9)N ;修复组为 (185 3.5± 387.4)N ,强化组为 (186 6 .1± 431.7)N。向空心侧孔螺钉中空部分注入PMMA ,未见椎弓根外或椎管内有PMMA溢出。周期抗屈试验中 ,添加PMMA可使空心侧孔螺钉耐受更大的负荷或在同等负荷?

Objective To evaluate the biomechanical effect of screws with hollow lateral holes infused with polymethylmethacrylate (PMMA) in pedicle of vertebral arch in strengthening the fixation. Methods A total of 32 fresh thoracolumbar vertebrae of 8 human bodies were employed in this study. Screws with hollow lateral holes of 6.5 mm in diameter were implanted into the pedicle of vertebral arch unilaterally (Group A), and massive screws of equivalent diameter were implanted into the pedicle of vertebral arch contralaterally (Group B) on 10 fresh thoracolumbar vertebrae (T 11 L 4). Then the screws of both groups were pulled out and F max test was employed. The hollow part of the screws and the screw track in Group A were filled with 3 5 ml PMMA. Then the screws were implanted unilaterally (Group C), and the screws with the screw track in Group B filled with prosthetic materials were implanted ultralaterally (Group D). Screws with hollow lateral holes were implanted into the pedicle of vertebral arch unilaterally, and massive screws of equivalent diameter were implanted into the pedicle of vertebral arch contralaterally on other 10 fresh thoracolumbar vertebrae. Then the screws were drilled for holes with the drilling bit for 3.5 mm in diameter. And then the drilled holes were filled with PMMA (Group E)and were twisted with screws (Group F), respectively. Periodical bending resistance test in screws with hollow lateral holes in pedicle of vertebral arch was made on the rest 12 vertebrae. And three point bending test was made on 10 screws with hollow lateral holes and 10 massive screws, respectively. Results F maxes were (855.0±207.5) N in Group A, (829.2±220.9) N in Group B,(1 924.4±383.2) N in Group C, (1 853.5±387.4)N in Group D,(1 943.3±535.8)N in Group E and (1 866.1±431.7)N in Group F. No PMMA was found in the vertebral canal or on the surface of pedicle of vertebral arch when PMMA was infused into the screws with hollow lateral holes, while PMMA was easily found in the vertebral canal or on the surface of the pedicle of vertebral arch in massive screws. The screws with hollow lateral holes infused with PMMA could receive more loadings or reduce fewer shifts under the same loadings compared with the controls. The max loading force of the screws with hollow lateral holes was (2 051.29±69.86)N, the elastic modulus was (23 941.8±1 467.4)N/mm 2 and the energy absorption was (40.187 3±1.469 3)J. While the max loading force of the massive screws was (2 075.01±117.57)N, the elastic modulus was (24 991.8±1 962.3)N/mm 2 and the energy absorption was (44.963 0±1.866 3)J. Conclusions PMMA can increase significantly the stabilization of the screws in pedicle of vertebral arch. And no PMMA is found in the vertebral canal or on the surface of pedicle of vertebral arch when PMMA is infused into the screws with hollow lateral holes, which is suitable for the fixation of screw mobilization and for the repair of the wound when screws are pulled out.