单节段与双节段椎弓根螺钉固定胸腰椎单椎体骨折的生物力学比较

目的:比较单节段与双节段椎弓根螺钉固定术固定胸腰椎单椎体骨折的生物力学效果。方法:在16具新鲜小牛胸腰椎标本(T11-L3)的L1椎体上制作不完全爆裂骨折模型,分为两组,分别行单节段与双节段椎弓根螺钉固定,对固定后的标本施加扭矩为4Nm的疲劳载荷共2000次,加载频率为0.5Hz,经脊柱三维运动测量系统测量正常、损伤、固定和周期性加载后固定节段前屈/后伸、左/右侧弯和左/右旋转运动时固定节段的运动范围。结果:单节段固定组前屈、后伸、侧屈、旋转稳定指数(SPI)分别为0.78、0.80、0.92、0.83,双节段固定组SPI分别为0.88、0.89、0.95、0.85,在前屈方向单节段固定组明显小于双节段固定组(P<0.01);疲劳后,单节段固定组SPI在前屈、后伸、侧屈、旋转方向分别降低0.05、0.03、0.05、0.11,降低值均大于双节段固定组,且在旋转和侧屈方向有显著性差异(旋转:P<0.01;侧屈:P<0.05)。结论:两种术式均可重建脊柱骨折即刻稳定性,效果无明显差异。在旋转、侧屈方向,双节段椎弓根螺钉固定术抗疲劳载荷效果优于单节段固定术。

Biomechanical evaluation of monosegmental versus bisegmental fixation by pedicle instrumentation in the management of thoracolumbar fracture

Objective:To compare the biomechanical properties of monosegmental pedicle instrumentation with those of bisegmental pedicle instrumentation.Method:Sixteen fresh frozen 6-week-old calf spines(T11-L3)were divided into two groups following the introduction of incomplete burst fracture at the vertebral body of L1.Monosegmental or bisegmental pedicle instrumentation was applied to the two groups to restore spinal stability.A cyclic load of 4Nm were applied to specimens at rate of 0.5Hz up to 2000 cycles.Segmental instability tests were performed on specimens in the condition of intact,injured,fixation respectively,followed by cyclic loading.Range of motion in flexion/extension,axial rotation,left/right lateral bending were determined by three-dimensional laser scanner.Result:The stability potential index(SPI)of monosegmental pedicle instrumentation in flexion/extension,lateral bending and axial rotation was 0.78,0.80,0.92,and 0.83 respectively,and the SPI in bisegmental group was 0.88,0.89,0.95 and 0.85 respectively.SPI of the former was significantly lower than the latter in flexion.(P<0.01).Following the fatigue test,SPI of monosegmental group in flexion/extension,lateral bending and axial rotation decreased 0.05,0.03,0.05,and 0.11 respectively,which were higher than bisegmental group especially in lateral bending(P<0.01),and axial rotation(P<0.05).Conclusion:Monosegmental pedicle instrumentation can provide the instant stability paraller to bisegmental instrumentation with respect to the reconstruction of unstable spine,however,it is inferior to bisegmental instrumentation in resisting lateral bending and axial rotation fatigue.