腰骶椎弓根螺钉翻修及强化固定后稳定性比较

Biomechanical stabilization in the revision and augmentation for lumbar and sacral pedicle screws

[目的]从生物力学角度评价腰骶椎弓根螺钉翻修及强化固定的稳定性。[方法]采用7具新鲜成人尸体L5S1椎体标本,于L5椎体首先置入5.5mm/45mm椎弓根螺钉,然后再置入7.0mm/55mm螺钉翻修,最后应用骨水泥强化固定;S1椎弓根置入初始螺钉为6.25mm/35mm、翻修螺钉为8.0mm/45mm、最后同样行骨水泥强化固定。在858MiniMTS生物力学实验机上分别测试各状态轴向最大拔出力及最大扭力矩。[结果](1)在L5,初始、翻修及骨水泥强化固定状态的最大把持力分别为(1680.7±242.8)N、(2410.3±366.1)N、(3273.0±688.5)N(P<0.05),最大扭力矩分别为(1006.1±205.3)N·mm、(1432.6±213.7)N·mm、(590.7±83.5)N·m(P<0.05);(2)在S1,初始、翻修及骨水泥强化的把持力分别为(926.3±274.2)N、(957.5±336.3)N、(1825.3±199.9)N,最大扭力矩分别为(667.6±88.3)N·mm、(681.4±79.4)N·mm、(558.8±97.2)N·mm;其中初始及翻修状态把持力及扭力矩均无明显差别(P>0.05),骨水泥强化固定后把持力明显增加、扭力矩明显减小(P<0.05)。[结论](1)L5椎弓根螺钉翻修时,螺钉直径增加1.5mm、长度增加10mm或骨水泥强化均可达到翻修固定的生物力学要求,增加脊椎稳定性,以骨水泥强化固定更为明显;(2)S1椎弓根螺钉翻修时,单纯增加螺钉直径和长度不能获得理想的稳定性,而骨水泥强化螺钉固定效果明显。

[ Objective] To evaluate the biomechanical stabilization of augmentation and revision of L5 and S1 pedicle screws. [ Method ] Seven lumbosacral spines from fresh adult cadavers were harvested, and dismembered into single vertebrae before testing. 5.5 mm/45 mm screws were implanted in L5 pedicles as control initially, then 7.0 mm/55 mm screws were used for the revision, and finally, the failed pedicles were augmented by cement. The original screws implanting in S1 pedicles were 6.25 mm/ 35 mm, the revision screws were 8.0 mm/45 mm, and also cement was used to salvage failed pedicles finally. The maximum pullout strength and insertional torque in all groups was tested on 858 Mini-MTS. [ Result] （ 1 ）For L5 vertebrae, the screw pullout strength in control, revision and augmented groups were （ 1 680.7 ± 242.8） N, （ 2 410.3 ± 366.1 ） N and （ 3 273.0 ± 688.5 ） N ,respectively with significant difference（ P 〈0.05 ）. The insertional torque of the lumbar groups was （ 1 006.1 ± 205.3 ） N · mm, （ 1 432.6 ± 213.7） N · mm and （ 590.7 ± 83.5 ） N · mm respectively with significant difference （ P 〈 0.05 ） ; （ 2 ） For S1 vertebrae, the pullout strength in control, revision screws was （926.3 ± 274.2） N, （957.5 ± 336.3 ） N respectively without obvious difference （ P 〉 0.05 ）. The strength of augmented screws was （ 1 825.3 ± 199.9） N, and much higher than other two groups （ P 〈 0.05 ）. The insertional torque was （667.6 ± 88.3 ） N · mm, （681.4 ± 79.4） N · mm and （558.84 ± 97.2） N · mm respectively without any difference of the torque between control and revision group （P 〉 0.05 ）, but the torque of augmented group was smaller than other two groups （ P 〈 0.05 ）. [ Conclusion ] （ 1 ） Increasing the screw diameter with 1.5 mm and the length with 10 mm of screws, or using cement to salvage failed Ls pedicles can all increase biomechanical stability ; （ 2 ） Increasing the screw length and diameter in S1 may not improve the pullout strength, but a good result is achieved by using cement augmentation.