传统与皮质骨轨迹椎弓根螺钉内固定术的生物力学对比

Biomechanical Comparison of Internal Fixation by Traditional and Cortical Bone Trajectory Pedicle Screw

目的 比较皮质骨轨迹(cortical bone trajectory,CBT)和传统轨迹(traditional trajectory,TT)椎弓根螺钉内固定对正常和骨质疏松性脊柱活动度(range of motion,ROM)和钉棒系统受力的影响。方法 建立正常骨质和骨质疏松腰椎L3~S1有限元模型,使用两种轨迹的螺钉钉棒系统对L4~5节段进行内固定,分别模拟人体前屈、后伸、左右侧弯和左右旋转6种生理载荷,对比两种内固定术式对正常和骨质疏松脊柱ROM和螺钉最大等效应力的影响。结果 对于两种骨质情况,相比于未置钉的节段模型,CBT和TT手术均显著降低了固定节段(L4~5)和下腰椎整个节段(L3~S1)ROM;但是,CBT组较TT组ROM下降的幅度略小,两者在屈伸时相近,而在侧弯和轴向旋转时差别明显;此外,在正常骨质模型和骨质疏松模型中,CBT组螺钉最大等效应力均较TT组有明显增加,正常骨质模型中CBT组螺钉最大等效应力在屈伸、侧弯、轴向旋转时比TT组分别提高27%、268%、58%。但在同时采用CBT技术时,骨质疏松模型较正常骨质模型有更小的螺钉应力分布。结论 骨质疏松条件下,相比于TT技术,CBT技术可以实现较高的螺钉应力,降低正常骨质条件下的螺钉应力集中;另外,CBT技术略微增加了各节段ROM,有利于术后脊柱生理功能的恢复。侧弯和轴向旋转会产生负面的力学效果,应避免这两种生理载荷。

Objective To compare the effects of cortical bone trajectory(CBT) and traditional trajectory(TT) pedicle screw internal fixation on the range of motion(ROM) and rod system stress of normal and osteoporotic(OP) spines.Methods The L3-S1 finite element models of normal and OP spines were established.The screw rod system with two kinds of trajectory was used for internal fixation of the L4-5 segment,so as to simulate six physiological loads,namely,flexion,extension,left/right bending,left/right rotation.The effects of two internal fixation methods on ROMs and maximum equivalent stress of screws in normal and OP spines were compared.Results For both bone conditions,CBT and TT significantly reduced ROM of the fixed segment(L4-5) and the entire segment of lower lumbar spine(L3-S1).However,the ROM decline of CBT group was slightly smaller than that of TT group,and their ROMs were similar under flexion and extension,but the ROM differences were significant under lateral bending and axial rotation.In addition,for both the normal and OP spine models,the maximum equivalent stress of screws in CBT group was significantly higher than that in TT group.Compared with TT group,the screw stress of CBT group in normal spine model under flexion and extension,lateral bending,axial rotation was increased by 27%,268% and 58%,respectively.However,when CBT technique was used at the same time,the OP spine model had a smaller screw stress distribution than the normal spine model.Conclusions Compared with TT technique,CBT technique can achieve higher screw stress under OP condition and reduce screw stress concentration under normal bone condition.In addition,CBT slightly increases ROMs of each segment,which is conducive to recovery of spinal physiological function after surgery.Lateral bending and axial rotation can produce negative mechanical effects,and these two physiological loads should be avoided.