Parent Stefan, Odell Tim, Oka Richard, Mahar Andrew, Newton Peter
Orthopaedics Unit, Ste Justine Hospital, Montreal, Quebec, Canada.
Spine (Phila Pa 1976). 2008 Aug 15;33(18):1966-9. doi: 10.1097/BRS.0b013e31817f12a9.
In vitro biomechanical investigation using human cadaveric vertebrae.
Evaluate the biomechanical differences in transverse plane vertebral body derotation maneuvers of thoracic pedicle screws in both medial and lateral directions.
Thoracic pedicle screws are thought to have better vertebral rotation control and better segmental scoliosis correction compared to hooks and wires. Little data exists regarding the biomechanical stability of pedicle screws when derotated in either medial or lateral directions.
Vertebral bodies (T4-L5) from 12 cadavers were instrumented with appropriate length pedicle screws while measuring insertion torque. Each body was anchored for independent loading in medial or lateral directions. Each screw was rotated around a rod using a constant length lever arm (30.5 cm) rigidly attached to the screw head simulating the posterior vertebral derotation maneuver. Yield torques (Nm) were analyzed using a one-way analysis of variance (P < 0.05).
Yield torques for both directions were significantly related to screw insertion torque (both P < 0.01). There were no statistical differences in yield torque between medial (12.0 +/- 4.9 Nm) or lateral (11.5 +/- 5.1 Nm) directions. There were no significant differences after normalization for insertion torque or screw length. Tests rotating the screw tip laterally demonstrated structural failure in the following percentages (anterolateral failure = 67%, posterior element failure = 33%, additional screw bending = 42%). Rotation medially demonstrated structural failures in the following percentages (canal penetration = 51%, posterior element failure = 49%, additional screw bending = 44%).
From these data, a surgeon performing a direct vertebral derotation using a 30 cm (12 in) lever would need to apply roughly 40 N (9 lbs) to causeanatomic failure. Adolescent patients would likely tolerate a greater force without bone failure given a greater bone density, yet, extreme caution is still recommended to prevent screw rotation either medially into the spinal canal or laterally into the chest.
使用人体尸体椎骨进行体外生物力学研究。
评估胸椎椎弓根螺钉在横向平面椎体去旋转操作中向内侧和外侧方向的生物力学差异。
与钩和钢丝相比，胸椎椎弓根螺钉被认为具有更好的椎体旋转控制和更好的节段性脊柱侧弯矫正效果。关于椎弓根螺钉在向内侧或外侧方向去旋转时的生物力学稳定性的数据很少。
从12具尸体上获取椎体（T4-L5），安装适当长度的椎弓根螺钉，同时测量插入扭矩。每个椎体在向内侧或外侧方向进行独立加载时进行固定。每个螺钉使用一个固定在螺钉头部的恒定长度杠杆臂（30.5厘米）围绕一根杆旋转，模拟椎体后路去旋转操作。使用单因素方差分析（P < 0.05）分析屈服扭矩（牛顿米）。
两个方向的屈服扭矩均与螺钉插入扭矩显著相关（两者P < 0.01）。内侧（12.0 +/- 4.9牛顿米）或外侧（11.5 +/- 5.1牛顿米）方向的屈服扭矩之间无统计学差异。在对插入扭矩或螺钉长度进行归一化后也无显著差异。向外侧旋转螺钉尖端的测试显示以下百分比的结构失效（前外侧失效 = 67%，后部结构失效 = 33%，额外的螺钉弯曲 = 42%）。向内侧旋转显示以下百分比的结构失效（椎管穿透 = 51%，后部结构失效 = 49%，额外的螺钉弯曲 = 44%）。
根据这些数据，使用30厘米（12英寸）杠杆进行直接椎体去旋转的外科医生需要施加约40牛顿（9磅）的力才能导致解剖学上的失效。青少年患者由于骨密度较高，可能能够承受更大的力而不发生骨质破坏，然而，仍建议极度谨慎以防止螺钉向内侧旋入椎管或向外侧旋入胸腔。
