伤椎传统短节段椎弓根螺钉固定与附加椎弓根螺钉固定后椎体生物力学稳定性的比较

Biomechanical comparison of additional injured-vertebrae screw and short-segment pedicle screw fixation for the management of thoracolumbar fracture

背景：目前通常采用在骨折椎相邻的上下椎弓根置入螺钉复位、固定的方法治疗胸腰椎骨折,但固定后容易出现伤椎高度恢复不够,融合节段后突畸形及内固定失败等并发症。一般认为固定螺钉少是内固定失败的重要原因。目的：比较在治疗胸腰椎骨折时,增加骨折椎椎弓根螺钉固定是否较传统后路短节段椎弓根螺钉固定有生物力学优势。设计、时间及地点：对比观察实验,于2007-10/2008-02在南方医科大学解剖实验室完成。材料：6具新鲜冰冻家猪胸腰椎标本T14-L3节段。方法：测量完整标本前屈-后伸、侧屈及旋转的稳定性后,通过重物撞击技术制造伤椎骨折模型,然后对每个标本行传统短节段椎弓根螺钉固定（4枚螺钉固定）及增加骨折椎椎弓根螺钉固定（6螺钉固定）。主要观察指标：①完整标本、4螺钉固定标本、6螺钉固定标本中前屈-后伸、侧屈、旋转的运动范围。②4螺钉固定及6螺钉固定在3个轴向运动范围与完整标本运动范围的比值。结果：6枚螺钉固定在前屈、后伸、侧屈状态下的运动范围均小于对照组和4枚螺钉固定组（P〈0.01）,6枚螺钉固定组和4枚螺钉固定组旋转运动范围均高于对照组（P〈0.01）。6枚螺钉固定在3个轴向运动范围与完整标本运动范围的比值均高于4枚螺钉固定。结论：附加伤椎置钉较传统的4枚螺钉固定可增加生物力稳定性,有助于椎体高度恢复的保持和复位。

BACKGROUND： Currently, reduction and fixation using pedicle screws at the fracture levels are applied to treat thoracolumbar vertebral fracture. However, incomplete recovery of injured vertebral height, kyphosis deformity at fused levels and failed internal fixations are complications after surgery. Generally, inadequate screws are regarded as reason of failure. OBJECTIVE： To investigate whether pedicle screws at the fracture levels （intermediat screws） exhibit biomechanical advantages in treating thoracolumbar vertebra/fracture over traditional posterior short-segment pedicle fixation. DESIGN, TIME AND SETTING： Comparative observation was performed at the Laboratory of Anatomy, Southern Medical University from October 2007 to February 2008. MATERIALS： Six fresh frozen porcine thoracolumbar spine ,specimens at T14-L3. METHODS： The stability of intact specimens in flexion, extension, lateral bending and torsion was examined. A fracture model was created using dropping technique. The fracture model was instrumented with short-segment pedicular screw fixation （4-screw construct） or the intermediate screws structure （6-screw construct）. MAIN OUTCOME MEASURES： The range of motion （ROM） of intact specimens, 4-screw contruct, and 6-screw construct in flexion, extension, lateral bending and torsion; ratio of ROM between two structure and the intact specimens. RESULTS： The 6-screw structure exhibited a smaller ROM in flexion, extension and lateral compared with the intact specimens and 4-screw construct （P 〈 0.01）; the ROM in torsion of 6-screw and 4-screw constructs was larger than the intact specimens （P 〈 0.01）, The ratios of ROM of 6-screw construct and intact specimens at 3 axial directions were larger than the ratios of 4-screw construct and intact specimens, CONCLUSION： The addition of intermediate screws at the fracture levels enhances the biomechanical stability of a short-segment pedicular fixation, and aids the height recovery and reduction of vertebral body.