Klöckner C, Rohlmann A, Bergmann G
Department of Orthopaedics and Orthopaedic Surgery, Friedrich Alexander University, Rathsberger Strasse 57, 91054 Erlangen, Germany.
Arch Orthop Trauma Surg. 2003 Oct;123(8):410-3. doi: 10.1007/s00402-003-0536-6. Epub 2003 Jun 21.
Pull-out of the cranial end-vertebra screw following a correction of a scoliosis with the VDS implant is a common complication, especially in the thoracic region. It requires an extension of the fusion length or at least reduces the outcome of the correction.
We therefore looked for a new approach to solve the problem of end-vertebra screw pull-out. It was postulated that the axial pull-out force at the end-vertebra screw is reduced by a screw with a hinge between the head and threaded part. The aim of our study was to calculate theoretically and then determine experimentally the screw pull-out force of regular and modified VDS screws with a hinge during lateral shifting of the screw heads in the frontal plane.
The use of a modified end-vertebra screw with a hinge on the cranial end vertebra of the correction region changes the shape of the threaded rod between the last two screws. Theoretically estimated, this leads to a reduction of the pull-out force to one-fourth of the value for the original VDS screw. Experimentally, the mean pull-out force for the modified end-vertebra screw was 110+/-8.6 N in comparison with the original screw, where the pull-out force was 214+/-7.2 N.
A reduction of screw pull-out can be expected when a screw with a hinge is used for the cranial end vertebra.
使用VDS植入物矫正脊柱侧弯后，颅端椎弓根螺钉拔出是一种常见并发症，尤其是在胸椎区域。这需要延长融合长度，或者至少降低矫正效果。
因此，我们寻找一种新方法来解决端椎螺钉拔出问题。据推测，通过在头部和螺纹部分之间设置铰链的螺钉，可以降低端椎螺钉的轴向拔出力。我们研究的目的是进行理论计算，然后通过实验确定在额面内螺钉头部侧向移位时，常规VDS螺钉和带有铰链的改良VDS螺钉的拔出力。
在矫正区域的颅端椎使用带有铰链的改良端椎螺钉，会改变最后两颗螺钉之间螺纹杆的形状。理论估计，这会使拔出力降低至原始VDS螺钉拔出力值的四分之一。实验中，改良端椎螺钉的平均拔出力为110±8.6N，而原始螺钉的拔出力为214±7.2N。
当在颅端椎使用带有铰链的螺钉时，预计螺钉拔出情况会减少。
