Essig David A, Miller Christopher P, Xiao Ming, Ivancic Paul, Jegede Kola, Badrinath Raghav, Smith Brian G, Grauer Jonathan N
Hospital for Special Surgery, New York, New York, USA.
Orthopedics. 2012 Oct;35(10):e1528-32. doi: 10.3928/01477447-20120919-24.
Current surgical treatment of idiopathic scoliosis involves the use of various segmental instrumentation. Various pedicle screws have allowed for improved correction. Although monoaxial screws have improved rotational control compared with polyaxial screws, their use may increase screw-bone interface or vertebral endplate forces if not inserted in an exactly straight trajectory. Uniaxial screws potentially decrease these forces while retaining the advantages of monoaxial screws with respect to better rotational control. The purpose of this study was to compare the vertebral endplate forces with monoaxial or uniaxial screws when being reduced to a rod. Thirty-two plastic, surrogate T11 vertebrae were prepared with monoaxial (n=16) or uniaxial (n=16) screws. Screw angles relative to inferior vertebral endplates were assessed with lateral radiographs. The vertebrae were fixed to a load cell, and loads were measured as the screw was reduced to a rod. Monoaxial screws demonstrated a linear progression of endplate force with increasing screw angle. Uniaxial screws demonstrated minimal endplate force until approximately 20°, coinciding with screwhead excursion angle. As this maximum excursion angle was passed, uniaxial screws demonstrated a force slope similar to the monoaxial screws.The measured endplate forces should be equivalent to forces at the screw-bone interface. The reduced force with uniaxial screws is expected to have less cranial-caudal plow potential as the screw is coupled to a rod for deformity correction. This could have potential implications for screw failure, especially in less dense bone.
目前特发性脊柱侧弯的外科治疗涉及使用各种节段性内固定器械。各种椎弓根螺钉有助于提高矫正效果。尽管单轴螺钉与多轴螺钉相比改善了旋转控制，但如果未以完全笔直的轨迹插入，其使用可能会增加螺钉-骨界面或椎体终板的受力。单轴螺钉在保持单轴螺钉在更好旋转控制方面优势的同时，有可能降低这些受力。本研究的目的是比较单轴或单平面螺钉在与棒连接复位时的椎体终板受力情况。制备了32个塑料替代T11椎体，其中16个使用单轴螺钉，16个使用单平面螺钉。通过侧位X线片评估螺钉相对于下位椎体终板的角度。将椎体固定在测力传感器上，并在螺钉与棒连接复位时测量受力。单轴螺钉的终板受力随螺钉角度增加呈线性增加。单平面螺钉在大约20°之前终板受力最小，这与螺钉头偏移角度一致。当超过这个最大偏移角度时，单平面螺钉的受力斜率与单轴螺钉相似。所测量的终板受力应等同于螺钉-骨界面的受力。当单平面螺钉与棒连接用于畸形矫正时，其受力减小预计会降低头-尾向的犁骨力。这可能对螺钉失效有潜在影响，尤其是在骨密度较低的情况下。
