膨胀式椎弓根螺钉翻修作用的生物力学效应

Biomechanical effect of the revision function of expansive pedicle screws

目的:测试并比较自行设计的膨胀式椎弓根螺钉(ExpansivePedicleScrew,EPS)与CDH,USS椎弓根螺钉翻修后的最大轴向拔出力及周期载荷疲劳寿命,评价EPS螺钉的翻修作用。方法:20个新鲜小牛腰椎随机数字表法分成甲、乙两组,每组10个椎体。两组椎体的椎弓根处均预先植入直径6.5mmCDH螺钉,拔出螺钉造成螺钉松动脱出的脊柱模型。随机在每个椎体的一侧椎弓根处拧入EPS螺钉,甲组对侧拧入USS螺钉,乙组拧入CDH螺钉(直径均为7.0mm×40mm),再次拔出螺钉,记录翻修的最大轴向拔出力。对CDH,USS,Tenor,EPS螺钉加载频率5Hz,载荷200～250N,150万次的周期载荷进行内固定器械周期载荷疲劳实验。结果:CDH,USS,EPS螺钉翻修时最大拔出力分别为(1206.8±597.4),(1522.2±392.1),(2161.5±555.4)N。EPS螺钉的最大拔出力均显著高于CDH,USS螺钉(P<0.05)。疲劳试验完成后,4种螺钉均未发生疲劳现象。结论:EPS螺钉较其他非膨胀式椎弓根螺钉有更优越的翻修可靠性。

AIM:To measure and compare the maximum axial pullout strength revised of newly designed expansive pedicle screw(EPS) with USS,CDH pedicle screws in revising calf lumber spine,and to evaluate the revision function of EPS. METHODS:Twenty fresh calf lumbar vertebrae harvested from 4 calf lumber spine were divided into 2 groups by means of random number table:group A and group B with 10 vertebral bodies in each group.CDH screws(6.5 mm×40 mm) were implanted in both pedicles of every vertebral body in the two groups.Pull out test was performed to make the loose screw prolapse model.For each pedicle pair,the salvage of one CDH screw was performed using a EPS screw in each group at random;In addition,the salvage of the other CDH screw was performed using a USS screw in group A,and the salvage of the other CDH screw was performed using a CDH screw in group B(the diameters of all the above three screws were 7.0 mm×40 mm).Pull out test was performed on the revised screws again,and then the maximum axial pullout strength was recorded.Cyclic loading fatigue test for internal fixation devices of CDH,USS,Tenor and EPS was performed at 5 Hz and 200-250 N for 1.5 million cycles. RESULTS:The maximum axial pullout strengths of the rescue CDH,USS and EPS screws were (1 206.8±597.4),(1 522.2±392.1) and (2 161.5±555.4) N respectively.The maximum axial pullout strength of EPS screws were all larger than those of CDH and USS screws significantly(P< 0.05).No screws were broken or bent at the end of fatigue tests. CONCLUSION:EPS screws offer better anchoring in revision surgery than most of the non expansive pedicle screws do.