Division of Neurological Surgery, Barrow Neurological Institute, Phoenix, Arizona 85013, USA.
J Neurosurg Spine. 2011 Feb;14(2):226-34. doi: 10.3171/2010.10.SPINE09785. Epub 2010 Dec 24.
Posterior screw-rod fixation for thoracic spine trauma usually involves fusion across long segments. Biomechanical data on screw-based short-segment fixation for thoracic fusion are lacking. The authors compared the effects of spanning short and long segments in the thoracic spine.
Seven human spine segments (5 segments from T-2 to T-8; 2 segments from T-3 to T-9) were prepared. Pure-moment loading of 6 Nm was applied to induce flexion, extension, lateral bending, and axial rotation while 3D motion was measured optoelectronically. Normal specimens were tested, and then a wedge fracture was created on the middle vertebra after cutting the posterior ligaments. Five conditions of instrumentation were tested, as follows: Step A, 4-level fixation plus cross-link; Step B, 2-level fixation; Step C, 2-level fixation plus cross-link; Step D, 2-level fixation plus screws at fracture site (index); and Step E, 2-level fixation plus index screws plus cross-link.
Long-segment fixation restricted 2-level range of motion (ROM) during extension and lateral bending significantly better than the most rigid short-segment construct. Adding index screws in short-segment constructs significantly reduced ROM during flexion, lateral bending, and axial rotation (p < 0.03). A cross-link reduced axial rotation ROM (p = 0.001), not affecting other loading directions (p > 0.4).
Thoracic short-segment fixation provides significantly less stability than long-segment fixation for the injury studied. Adding a cross-link to short fixation improved stability only during axial rotation. Adding a screw at the fracture site improved short-segment stability by an average of 25%.
胸椎创伤后路钉棒固定通常需要长节段融合。胸椎融合短节段钉棒固定的生物力学数据尚缺乏。作者比较了胸椎短节段和长节段固定的效果。
准备了 7 个人体脊柱节段（T-2 到 T-8 的 5 个节段；T-3 到 T-9 的 2 个节段）。通过施加 6Nm 的纯力矩来引起屈伸、侧屈和轴向旋转，同时通过光电学方法测量三维运动。对正常标本进行了测试，然后在切断后韧带后在中间椎骨上造成楔形骨折。测试了 5 种器械条件，如下：步骤 A，4 级固定加交叉固定；步骤 B，2 级固定；步骤 C，2 级固定加交叉固定；步骤 D，2 级固定加骨折部位的螺钉（指数）；步骤 E，2 级固定加指数螺钉加交叉固定。
长节段固定在伸展和侧屈时显著更好地限制了 2 级运动范围（ROM），比最刚性的短节段结构要好得多。在短节段结构中添加指数螺钉显著降低了屈伸、侧屈和轴向旋转时的 ROM（p < 0.03）。交叉固定降低了轴向旋转 ROM（p = 0.001），但不影响其他加载方向（p > 0.4）。
与长节段固定相比，胸椎短节段固定在研究的损伤中提供的稳定性显著降低。向短固定添加交叉固定仅在轴向旋转时改善了稳定性。在骨折部位添加螺钉将短节段稳定性平均提高了 25%。
