Yüksel K Zafer, Adams Mark S, Chamberlain Robert H, Potocnjak Mark, Park Sung Chan, Sonntag Volker K H, Crawford Neil R
Spinal Biomechanics, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, 350 W. Thomas Road, Phoenix, AZ 85013, USA.
Spine J. 2007 May-Jun;7(3):286-91. doi: 10.1016/j.spinee.2005.12.007. Epub 2006 Sep 11.
Extrapedicular screws are placed more laterally than intrapedicular screws and pass through the transverse process or rib head before entering the vertebral body. These screws are sometimes placed to salvage failed pedicle screws, but the change in pullout resistance of extrapedicular screws after salvage has not been quantified.
To quantify the pullout resistance of thoracic extrapedicular screws compared with intrapedicular screws and the pullout resistance of newly inserted screws compared with extrapedicular screws used as salvage for failed intrapedicular screws.
In vitro paired comparison of screw pullout resistance in isolated thoracic vertebrae.
Tapered monoaxial pedicle screws were inserted in the left or right pedicle of 11 human cadaveric thoracic vertebrae. An extrapedicular screw was inserted on the contralateral side. Both screws were pulled out axially at 0.5 mm/s using a servohydraulic test frame while applied load was recorded. Then a fresh extrapedicular screw was inserted as a salvage screw on the intrapedicular screw side and pulled out.
In uncompromised vertebrae, the pullout strength of extrapedicular screws was 80+/-32% of that of intrapedicular screws (p=.073, repeated-measures one-way analysis of variance/Tukey). Salvage screws restored pullout strength to 65+/-30% of that of intrapedicular screws (p=.003).
Extrapedicular screws provided comparable but slightly lower pullout resistance to intrapedicular screws in uncompromised vertebrae. They are therefore a feasible salvage technique when a compromised pedicle precludes reinsertion of an intrapedicular screw, but the salvage screw is significantly weaker than the original screw.
椎弓根外侧螺钉的置入位置比椎弓根螺钉更靠外，在进入椎体之前穿过横突或肋骨头。这些螺钉有时用于挽救失败的椎弓根螺钉，但挽救后椎弓根外侧螺钉的拔出阻力变化尚未量化。
量化胸椎椎弓根外侧螺钉与椎弓根螺钉相比的拔出阻力，以及新插入螺钉与用于挽救失败的椎弓根螺钉的椎弓根外侧螺钉相比的拔出阻力。
在离体胸椎上进行螺钉拔出阻力的体外配对比较。
将锥形单轴椎弓根螺钉插入11具人类尸体胸椎的左侧或右侧椎弓根。在对侧插入一枚椎弓根外侧螺钉。使用伺服液压试验架以0.5mm/s的速度轴向拔出两枚螺钉，同时记录施加的载荷。然后在椎弓根螺钉侧插入一枚新鲜的椎弓根外侧螺钉作为挽救螺钉并拔出。
在未受损的椎体中，椎弓根外侧螺钉的拔出强度为椎弓根螺钉的80±32%（p = 0.073，重复测量单因素方差分析/ Tukey检验）。挽救螺钉将拔出强度恢复至椎弓根螺钉的65±30%（p = 0.003）。
在未受损的椎体中，椎弓根外侧螺钉提供的拔出阻力与椎弓根螺钉相当，但略低。因此，当受损的椎弓根妨碍重新插入椎弓根螺钉时，它们是一种可行的挽救技术，但挽救螺钉明显比原螺钉弱。
