柔性和动态椎弓根螺钉固定系统抗压缩性能的生物力学研究

Biomechanical evaluation of flexible and dynamic pedicle screw instrumentations under compressive axial loads

目的比较3种柔性和动态固定在8个不同方位上承受轴向压缩载荷时的椎间盘高度，并与完整节段和传统的椎弓根螺钉固定比较，以评价柔性和动态的椎弓根螺钉固定的抗压缩性能。方法采用新鲜成年家猪k腰椎标本8例。切除后部结构后，L3-4分别行3种柔性和动态固定，以及常规的椎弓根螺钉固定。在8个压缩点分别对标本施加400N的前屈压缩、后伸压缩、左／右侧弯压缩、左／右侧前压缩、左／右侧后压缩载荷。通过Optotrak测量脊柱三维运动，计算L3-4椎间盘前缘高度变化。测试状态包括：完整状态，损伤状态下5．5mm钛棒固定、3．0mm钛棒固定、滑动棒固定、球窝连接固定。结果在前屈、侧弯、侧前压缩方向上，完整状态与各固定组间的抗压缩能力未显示出统计学差异（P〉O．05）；在后伸压缩方向上，3．0mm棒固定组的压缩高度与完整状态、5．5mm固定组间显示出统计学差异（P〈0．05），而其余组问的压缩高度无显著性差异；在侧后压缩上，损伤状态下各器械固定组均与完整状态有显著性差异（P〈0．05），同时3．0mm固定组与球窝连接组之间的压缩高度值也存在显著性差异。结论柔性及动态固定后脊柱的抗压缩性能都得到提高。滑动棒固定整体上取得了与传统坚强固定相当的抗压缩性能。球窝连接固定在侧前或前屈压缩时抗压缩性能较差，但在后伸和侧后压缩上较好。细棒固定在后伸及侧后压缩方向上抗压缩性能相对不足。

Objective To evaluate the intervertebral disc heights of porcine lumbar spines implanted with 3 flexible/dynamic pedicle screw fixations under axial compressive force at 8 locations, and compare it with conventional pediele screw fixation. Methods Eight fresh porcine spine specimens （I-Ls） were collected. 3 flexible /dynamic and 1 conventional pedicle screw fixations were applied to -L4 segment following resection of the posterior structures. Each specimen was subjected to flexion-compression, extensioncompression, lateral-bending-compression, lateral-flexion-compression and lateral-extension-compression with a compressive force of 400N on the top of the specimen at 8 locations. 3D motion was measured using the Optotrak, and the L3-L4 anterior disc height was calculated. The specimen conditions included the intact and instrumentation with 5.5 mm rod, 3ram rod and sliding rod, and with ball-socket joint pedicle screws. Results Under the flexion-compression, lateral-bending-compression and lateral-flexion compression, there were no significant differences in the disc height change between the intact and each fixation condition （ P〉 0.05 ）. In extension-compression, the disc height change with the 3.0 mm rod was significantly different from the intact or the fixations with 5.5mm rod （P〈 0.05）,while no significant difference among other groups were detected; In lateral-extension-compression, there was significant difference in the disc height change between each fixation and intact status （P〈0.05）, and between fixations with 3.0mm rod and the ball-socket joint screw fixation （P〈0.05）. Conclusions Flexible/dynamic fixations enhanced the compressive stability of lumbar spine when compared to the intact status. The fixation with sliding rods achieved compressive stability close to the conventional pedicle screw fixation. The compressive stability with ball-socked joint screw fixation was comoarable to the conventional fixation in extension-comlression and lateralextension-compression, but waspoor in flexion-compression or lateral-flexioncompression. Fixation with thinner rods was not strong enough in extension-compression or