螺钉F角对后路单节段固定稳定性的影响

目的　比较4组不同椎弓根螺钉置入方式对后路单节段固定生物力学稳定性的差异。方法　将24具新鲜小牛胸腰椎标本(T11~L3)分为4组，用椎体楔行切除法在L1椎体上制作严重压缩性骨折模型，用4组不同进钉角度行后路单节段椎弓根钉内固定，对固定后的标本施加频率为1.0Hz的前屈／后伸、左／右侧屈和左／右旋转疲劳载荷各3000次，经脊柱三维运动测量系统测量正常、损伤、固定和疲劳后4种状态下固定节段(T13~L1)前屈／后伸、左／右侧屈和左／右旋转运动范围，将其标准化为稳定指数后比较四组内固定方式在4种状态下6个载荷方向上稳定性的差异。结果　4组固定均能显著提高骨折模型在6个载荷方向上的稳定性(P<0.01)，而且显著强于正常标本组(P<0.01)，但四组间无显著性差异(P>0.05)；疲劳试验后4组标本在6个载荷方向上的稳定性均小于各自疲劳试验前，但两者间无显著性差异(P>0.05)，且4组间无显著性差异(P>0.05)。结论　只要保证螺钉在椎弓根及椎体内且伤椎螺钉避开骨折区域，螺钉的F角大小不会影响单节段固定的即刻稳定性及疲劳后稳定性。

Biomechanical Analysis of Posterior Monosegmental Fixation:Effect of the Angle of Pedicle Screw Implanted

Objective Compare the biomechanical properties of four groups with different posterior monosegmental fixation and make the evaluation. Method Twenty four fresh frozen of one-week-old calf spines (T11-L3) were divided into four groups following the introduction of incomplete compression fracture at the vertebral body of L1 by the method of excision. Four types of monosegmental fixation were applied to the four groups respectively to restore spinal stability. A cyclic loading were applied to the specimens at rate of 1.0 Hz up to 3000 cycles in flexion/extension, left/right lateral bending and left/right rotation respectively. Segmental stability (T13-L1) tests were then performed on the specimens in the condition of intact, injured, fixation respectively. Range of motion(ROM)in flexion/extension, left/right axial rotation, left/right lateral bending were determined by three dimensional laser scanner. Then the ROM was standardized into stability potential index(SPI)to compare the stability in six loading directions of four types of fixation in four conditions. Result All of the four groups with monosegmental fixation could significantly increase the stability in six motion directions when compared to their injury condition(P<0.01), and significant superior than that of intact condition(P<0.01), but there was no significant difference among the four groups(P>0.05).The stability in six motion directions after cyclic loading was inferior when compared to that of before cyclic loading respectively, but there was no significant difference in between(P>0.05), or among the four groups(P>0.05). Conclusions As long as it could ensure to implant the pedicle screw into pedicle and vertabra, and avoid the fractured areas in the affected segment, the angle of pedicle screw directed to superior or inferior endplate will not affect both the instant and post-fatigue stability.