颈椎椎间孔螺钉、侧块螺钉及椎弓根螺钉的生物力学强度比较

目的比较椎间孔螺钉(paravertebral foramen screws,PVFS)、侧块螺钉(lateral mass screws,LMS)与椎弓根螺钉(pedicle screws,PS)的生物力学强度。方法选取8具新鲜冰冻尸体,男4具、女4具,死亡时年龄(45.3±11.2)岁。CT检查排除骨折、畸形、感染、肿瘤等疾病引起的骨质破坏或其他异常,最终筛选出30个C3~C6颈椎脊椎。将制备完成的颈椎节段标本顺序编号,应用随机数字表法将其随机分为三组,每组10个标本,分别用于双侧置入椎间孔螺钉(4.5 mm×12 mm螺钉)、侧块螺钉(3.5 mm×14 mm)与椎弓根螺钉(3.5 mm×24 mm螺钉)。随机选取一侧进行直接拔出力测试(速度5 mm/min),另一侧进行疲劳测试(位移±1.0 mm,频率1 Hz,循环500次)及残余拔出力测试。结果椎间孔螺钉的直接拔出力为(327.10±17.07)N,侧块螺钉为(305.71±11.63)N,椎弓根螺钉为(635.67±22.82)N。椎间孔螺钉的残余拔出力为(265.62±18.19)N,侧块螺钉为(192.80±17.10)N,椎弓根螺钉为(494.89±41.79)N。椎间孔螺钉、侧块螺钉和椎弓根螺钉的残余拔出力较直接拔出力均有不同程度降低(tPVFS=7.795,tLMS=17.267,tPS=9.349,P<0.001),分别下降了18.8%、36.93%和22.15%。椎弓根螺钉的直接拔出力高于椎间孔螺钉和侧块螺钉(t=34.245,t=40.741,P<0.001),椎间孔螺钉略高于侧块螺钉(t=3.275,P=0.004)。残余拔出力椎弓根螺钉最高,椎间孔螺钉次之,侧块螺钉最小(F=314.619,P<0.001)。椎间孔螺钉的首次循环载荷和首次达到设定位置时载荷均高于侧块螺钉(t=3.625,P=0.002;t=5.388,P<0.001)和椎弓根螺钉(t=2.575,P=0.019;t=2.680,P=0.015),侧块螺钉与椎弓根螺钉的差异无统计学意义(t=0.609,P=0.550;t=1.953,P=0.067)。椎间孔螺钉与椎弓根螺钉的末次循环载荷均高于侧块螺钉(t=5.341,P<0.001;t=3.439,P=0.003),但椎间孔螺钉与椎弓根螺钉的差异无统计学意义(t=1.606,P=0.126)。结论椎间孔螺钉的直接拔出力略高于侧块螺钉,残余拔出力明显高于侧块螺钉,抗疲劳性能与椎弓根螺钉相近并明显优于侧块螺钉,因此,颈椎椎间孔螺钉具有作为侧块螺钉和椎弓根螺钉有效替代的潜能。

Comparison of biomechanical properties of cervical paravertebral foramen screws,lateral mass screws and pedicle screws

Objective To investigate and compare the biomechanical strength of paravertebral foramen screws(PVFS),lateral mass screws(LMS)and pedicle screws(PS).Methods A total of 30 human cervical spine vertebrae(C3-C6)were harvested from 8 fresh-frozen cadaver specimens whose mean age was 45.3±11.2 years at death.The vertebrae were randomly divided into three groups for specific screws.For each vertebra,one side was randomly chosen for direct pullout strength test(speed 5 mm/s),and the other side for fatigue test(displacement±1.0 mm,frequency 1 Hz,500 cycles)and residual pullout strength test.4.5 mm×12 mm screws were used for PVFS,3.5 mm×14 mm screws for LMS,and 3.5 mm×24 mm screws for PS.Results The direct pullout strength was 327.10±17.07 N for PVFS,305.71±11.63 N for LMS,and 635.67±22.82 N for PS.The residual pullout strength was 265.62±18.19 N for PVFS,192.80±17.10 N for LMS,and 494.89±41.79 N for PS.The residual pullout strength of PVFS,LMS and PS respectively,compared with the direct pullout strength,decreased by 18.8%,36.93%and 22.15%(tPVFS=7.795,tLMS=17.267,tPS=9.349,P<0.001).The direct pullout strength of PS was higher than that of PVFS and LMS(t=34.245,t=40.741,P<0.001),as well as PVFS was slightly higher than LMS(t=3.275,P=0.004).The residual pullout strength of PS was the highest,PVFS was the second,and LMS was the smallest(F=314.619,P<0.001).For the fatigue test,the load at the first cycle and the first time when the set position was reached of PVFS were higher than those of LMS(t=3.625,P=0.002;t=5.388,P<0.001)and PS(t=2.575,P=0.019;t=2.680,P=0.015),but there was no difference between those of LMS and PS(t=0.609,P=0.550;t=1.953,P=0.067).The load at the last cycle of PVFS and PS was higher than that of LMS(t=5.341,P<0.001;t=3.439,P=0.003),while there was no difference between PVFS and PS(t=1.606,P=0.126).Conclusion The direct pullout strength of PVFS was slightly higher than that of LMS,and the residual pullout strength was significantly higher than LMS.The property of fatigue resistance of PVFS was similar to PS and obviously better than LMS.In summary,PVFS can be used as an effective substitute for LMS and PS.