University of Louisville School of Medicine, 500 South Preston Street. Instructional Building, Room 305. Louisville, KY, USA.
Norton Leatherman Spine Center, 210 East Gray Street, Suite 900, Louisville, KY, USA.
Spine J. 2022 Jan;22(1):168-173. doi: 10.1016/j.spinee.2021.07.010. Epub 2021 Jul 15.
There are situations that require the replacement of pedicle screws. They are often exchanged when loose or broken or to accommodate a different sized rod or pedicle screw system. Traditionally, pedicle screws are replaced by up-sizing the core diameter until an interference fit is obtained. However, this method carries a risk of pedicle screw breach.
To determine if dual pitch screws, with cancellous pitch in the vertebral body and cortical pitch throughout the pedicle, allows for in-line screw revision without upsizing screw diameter.
Cadaveric biomechanical Study PATIENT SAMPLE: Not applicable OUTCOME MEASURES: Not applicable METHODS: Pedicle screws were tested in the lumbar vertebrae from eleven cadavers. Standard pitch 5.5 mm screws were inserted and loaded using a "break-in" protocol. Screws were removed and replaced with one of four screw types: 5.5 mm Standard Pitch, 5.5 mm Dual Pitch, 6.0 mm Standard Pitch, or 6.0 mm Dual Pitch. Failure testing was done using a stepwise increasing cyclic loading protocol for 100 cycles at each increasing load level. The loading consisted of a combined axial and bending load simulating the load seen by the most inferior screw.
Failure was consistent, with the tip of the screw displacing inferiorly into the vertebral body while simultaneously pulling out. Failure strength was lowest in the 5.5mm Standard (135.8±29.4N) followed by 6.0mm Standard (141.8±38.6N), 5.5mm Dual (158.1±53.8N), and 6.0mm Dual (173.6±52.1N, p=.023). There was no difference in the failure strength between the 5.5mm Dual and 6.0mm Standard. Lumbar level (p=.701) and donor spine (p=.062) were not associated with failure strength.
After pedicle screw removal, screws with a larger core diameter or with a dual pitch have similar failure strengths. Dual pitch screws may allow for in-line revision of screws without upsizing screw diameter, minimizing the risk of pedicle breach or fracture.
Dual pitch screws, with cancellous pitch in the vertebral body and cortical pitch through the pedicle, allows for in-line revision of pedicle screws without upsizing screw diameter; reducing the risk of pedicle breach or fracture when exchanging screws.
有些情况下需要更换椎弓根螺钉。当螺钉松动、断裂或需要适配不同大小的棒或椎弓根螺钉系统时，通常会更换螺钉。传统上，通过增大核心直径直到获得过盈配合来更换椎弓根螺钉。然而，这种方法存在椎弓根螺钉破裂的风险。
确定是否可使用带松质骨螺距的双螺距螺钉（螺钉的椎体部分为松质骨螺距，而穿过椎弓根部分为皮质骨螺距），在不增大螺钉直径的情况下进行螺钉的原位修正。
尸体生物力学研究
不适用
11 具尸体的腰椎进行了椎弓根螺钉测试。标准螺距 5.5mm 螺钉插入并使用“磨合”方案加载。移除螺钉并用以下四种螺钉类型之一更换：5.5mm 标准螺距、5.5mm 双螺距、6.0mm 标准螺距或 6.0mm 双螺距。使用逐步增加的循环加载方案在每个增加的载荷水平下进行 100 个循环的失效测试。加载包括模拟最下方螺钉所受的轴向和弯曲组合载荷。
螺钉尖端向下位移至椎体，同时向外拔出，失效模式一致。5.5mm 标准螺钉（135.8±29.4N）的失效强度最低，其次是 6.0mm 标准螺钉（141.8±38.6N）、5.5mm 双螺距螺钉（158.1±53.8N）和 6.0mm 双螺距螺钉（173.6±52.1N，p=.023）。5.5mm 双螺距螺钉与 6.0mm 标准螺钉的失效强度无差异。腰椎水平（p=.701）和供体脊柱（p=.062）与失效强度无关。
在椎弓根螺钉取出后，使用更大核心直径或双螺距的螺钉具有相似的失效强度。双螺距螺钉可在不增大螺钉直径的情况下进行椎弓根螺钉的原位修正，从而降低椎弓根破裂或骨折的风险。
带松质骨螺距的双螺距螺钉（螺钉的椎体部分为松质骨螺距，而穿过椎弓根部分为皮质骨螺距）允许在不增大螺钉直径的情况下进行椎弓根螺钉的原位修正，降低更换螺钉时椎弓根破裂或骨折的风险。
