下颈椎经关节螺钉与侧块钉棒固定的生物力学比较

Biomechanical study of transfacet screws and lateral mass screw-rod construct fixation in the lower cervical spine

目的 ：比较下颈椎经关节螺钉与侧块钉棒系统固定的生物力学特点。方法 ：采用8具新鲜尸体下颈椎标本（C5~T1）,用牙托石膏粉包埋后,通过脊柱试验机对标本施加最大2.0Nm纯力偶矩,在不同测试状态下,包括完整（A组）、C5/6后方韧带复合体切除（B组）、C5~C7经关节螺钉固定（C组）、C5~C7侧块钉棒系统固定（D组）,测量屈伸、侧弯及旋转方向上的三维运动范围（ROM）。在C6椎体前缘粘贴应变片,测量不同状态下椎体前柱载荷变化。结果：A组C5/6节段屈伸、侧弯和旋转方向上的ROM分别为13.6°±1.2°、6.1°±0.5°、4.2°±1.6°;B组为14.4°±1.2°,6.4°±0.6°,4.8°±0.8°,C组为2.8°±0.7°、0.7°±0.3°、0.4°±0.1°,D组为1.2°±0.3°、0.5°±0.2°、0.8°±0.3°,在屈伸方向上B组的ROM较A组明显增大（P〈0.05）,C组和D组在各方向上均较A组和B组明显减小（P〈0.05）;在屈伸方向上,C组与D组比较有统计学差异（P〈0.05）,在侧弯和旋转方向上,C组和D组无统计学差异（P〉0.05）。A组C6/7节段屈伸、侧弯和旋转方向上的ROM分别为12.3°±1.4°、5.5°±1.2°、2.7°±0.9°;B组为12.0°±1.3°、5.6°±1.0°、2.8°±0.9°,C组为2.9°±0.9°、0.4°±0.2°、0.4°±0.1°,D组为1.2°±0.3°、0.4°±0.1°、0.7°±0.3°,A、B两组在各方向上的ROM无显著性差异（P〉0.05）;在屈伸方向上,C组和D组的ROM有统计学差异（P〈0.05）,在侧弯和旋转方向上,两组无统计学差异（P〉0.05）。C组C6椎体前柱的应变在侧弯方向上较A组明显减小（P〈0.05）,D组在前屈、后伸、侧弯方向上较A组明显减小（P〈0.05）,C、D组在前屈方向上比较有统计学差异（P〈0.05）。结论：下颈椎后方韧带复合体损伤可造成屈伸和侧弯方向上失稳,经关节螺钉固定在轴向旋转和侧弯方向上与侧块钉棒系统固定效果相似,但限制屈伸运动的能力较弱。

Objectives： To compare the characteristics of biomechanics of transfacet screws and lateral mass screw-rod constructs. Methods： Eight fresh cadaveric cervical specimens（C5-T1） were harvested and embedded in dental plaster. Biomechanical studies of samples were performed under intact（group A）, injury（group B, following the C5/6 PLC section） and various fixation statements（group C, with the transfacet screws place-ment; group D, with the lateral mass screw-rod constructs placement） by using a spinal mechanical testing machine, while applying a constant moment of 2.0Nm in flexion-extension, left-right lateral bending, and leftright axial rotation directions for three cycles. Strain gauges were positioned on the C6 vertebra to measure the change of load of anterior column. Results： On the level of C5/6, the ROM of group A was 13.6°±1.2°（flexion-extension）, 6.1°±0.5°（left-right lateral bending）, 4.2°±1.6°（left-right axial rotation） respectively; the ROM of group B was 14.4°±1.2°（flexion-extension）, 6.4°±0.6°（left-right lateral bending）, 4.8°±0.8°（left-right axial rotation） respectively; the ROM of group C was 2.8°±0.7°（flexion-extension）, 0.7°±0.3°（left-right leteral bending）, 0.4°±0.1°（left-right axial rotation） respectively; the ROM of group D was 1.2°±0.3°（flexion-extension）,0.5°±0.2°（left-right leteral bending）, 0.8°±0.3°（left-right axial rotation） respectively. The ROM of group B increased significantly compared with that of group A in flexion-extension（P〈0.05）. The ROM of group C and D decreased significantly compared with that of group A and B in all directions（P〈0.05）. The ROM of group C in flexion-extension was different with that of group D（P〈0.05）; the ROM of group C and D was comparable in left-right lateral bending and axial rotation（P〉0.05）. On the level of C6/7, the ROM of group A was 12.3°±1.4°（flexion-extension）, 5.5°±1.2°（left-right lateral bending）, 2.7°±0.9°（left-right axial rotation） respectively; the ROM of group B was 12.0°±1.3°（flexion-extension）, 5.6°±1.0°（left-right lateral bending）, 2.8°±0.9°（left-right axial rotation） respectively; the ROM of group C was 2.9°±0.9°（flexion-extension）, 0.4° ±0.2°（left-right leteral bending）, 0.4°±0.1°（left-right axial rotation） respectively; the ROM of group D was 1.2°±0.3°（flexion-extension）,0.4° ±0.1°（left-right leteral bending）, 0.7° ±0.3°（left-right axial rotation） respectively. The difference betweem group A and B was not significant in all directions（P〉0.05）. The ROM of group C was different with that of group D in flexion-extension（P〈0.05）. The ROM of group C and D was not different in lateral bending and axial rotation（P〉0.05）. The strain of group C on C6 level was reduced significantly in lateral bending when compared with that of group A（P〈0.05）; the strain of group D was reduced significantly in flexion, extension and lateral bending when compared with that of group A（P〈0.05）; and the strain of group D was reduced significantly in flexion when compared with that of group C（P〈0.05）. Conclusions： The present study identifies that the injury of PLC may result in instability in flexion-extension and lateral bending. Transfacet screw fixation is weaker than the lateral mass screw-rod fixation in flexion-extension, while is not different in lateral bending and axil rotation.