椎弓根螺钉不同翻修方法的生物力学研究

Biomechanical study of various pedicle screw revision techniques

目的研究增加螺钉直径和长度、钉孔内植骨以及聚四氟乙烯膨胀螺栓强化这四种椎弓根螺钉翻修方法所各自产生的最大轴向拔出力和最大置入扭矩变化,以确定椎弓根螺钉的最佳翻修方法。方法将6具成人T10～L5椎体标本,分为:(1)增加椎弓根螺钉直径组,(2)延长椎弓根螺钉长度组,(3)增加直径+延长长度组,(4)植骨组,(5)聚四氟乙烯膨胀螺栓组,(6)退出后再置组。将最初置入的直径5.0mm、长40mm螺钉时所测得的最大扭矩和最大轴向拔出力作为对照组数据;记录翻修螺钉最大扭矩和最大轴向拔出力与相应对照组数据之间的变化量,各组之间结果行统计学分析。结果在增加螺钉直径和(或)长度的方法中,当螺钉直径增加2mm且长度增加10mm时,扭矩和最大轴向拔出力的增加最明显,分别为37.06%和18.22%;螺钉直径增加2mm,扭矩增加20.15%,最大轴向拔出力增加19.99%;螺钉直径增加1mm、长度增加5mm,扭矩增加19.23%,最大轴向拔出力增加10.07%;螺钉长度单纯增加5mm与10mm,扭矩分别下降32.80%和14.02%,最大轴向拔出力分别下降27.36%和增加43.25%;钉孔内植骨后再置入螺钉,扭矩和轴向拔出力分别下降了14.99%和29.34%;聚四氟乙烯膨胀螺栓强化后再置入螺钉,扭矩显著增加,而轴向拔出力下降了37.40%;螺钉退出后再置,扭矩下降了34.22%。结论螺钉直径增?

Objective To determine the best method of revision for failed pedicle screw by investigating the change in maximum insertional torque and axial pullout strength after placing a larger diameter and/or longer screw or augmenting the failed hole with bone shims or PMMA. Methods Six fresh male adult cadaveric spines from T10-L5 were harvested. These specimens, aging from 23 to 51 years with an average of 36.7 years, were divided into six groups: 1)Using a larger diameter screw; 2)Using a longer screw; 3)Using a larger and longer screw; 4)Augmenting with bone shims; 5)Augmenting with PMMA; and 6)Reinsertion after being backed out. The first three groups were subdivided into two groups. Maximum insertional torque and axial pullout strength of each original screw were recorded as control data. Change of maximum insertional torque and axial pullout strength between original and corresponding revision screws were noted. Measurements were analyzed using one-way ANOVA statistically by SPSS10.0. Insertional torque change after simply removing and replacing a 5.0 mm×40 mm screw was also measured. Results Among the changes in pedicle dimensions, the greatest improvement in peak insertional torque and axial pullout strength occurred when using a 2 mm larger and 10 mm longer screw, with an increase of 37.06% and 18.22%; a 2 mm larger screw increased peak insertional torque and axial pullout strength by 20.15% and 19.99% respectively, while a 1 mm larger and 5 mm longer screw increased by 19.23% and 10.07% respectively; use of a 5 mm or 10 mm longer screw decreased peak insertional torque by 32.80% and 14.02% respectively, with axial pullout strength down by 27.36% and up by 43.25% respectively. Use of bone shims caused a decrease of the insertional torque and axial pullout strength by 14.99% and 29.34% respectively. Hole augmentation with PMMA lead to a significant increase in insertional torque but a decrease in axial pullout strength by 37.40%. Simply removing and replacing an original screw resulted in a decrease in insertional torque by 34.22%. Conclusion Revision for pedicle screw is most effective when using a 2 mm larger diameter screw, next by using a 1 mm larger diameter and 5 mm longer screw. Use of a bone shim should be avoided. The efficacy of hole augmentation with PMMA need to be further investigated.