University of Montréal, Hôpital du Sacré Cœur, 5400 Gouin Ouest, Local J-3245, Montréal, Québec, Canada H4J 1C5.
Injury. 2013 Oct;44(10):1358-62. doi: 10.1016/j.injury.2013.06.013. Epub 2013 Jul 11.
Locking plates have become ubiquitous in modern fracture surgery. Recently, manufacturers have developed locking plates with polyaxial screw capabilities in order to optimise screw placement. It has already been demonstrated that inserting uniaxial locking screws off axis results in weaker loads to failure. Our hypothesis was that even implants specifically designed for polyaxial insertion would experience a drop-off in resistance when using non-perpendicular screws.
Four different types (one monoaxial and three polyaxial locking plates) of readily available small fragment plates were tested. A biomechanical model was developed to test the screws until failure (defined as breakage and rapid loss of >50% force). Screws were inserted at 0, 10 and 15°.
The standard monoaxial locking mechanism sustained saw a 60% reduction in force (332N vs. 134N) when screws were inserted cross-threaded at 10°. Two polyaxial systems saw similar significant reductions in force of 45% and 34%, respectively at 15°. A third system utilizing an end cap locking mechanism showed highly variable results with large standard deviations. Polyaxial screws showed on average only limited reduction at 10 degrees of insertion angle.
Newer designs of locking plates have attractive properties to allow more surgical options during fixation. However this freedom comes at the price of reduced force. Our results show that the safe zone for inserting these screws is closer to 20°, rather than the 30° indicated by the manufacturers. Also, the various polyaxial locking mechanisms seem to influence the overall resistance of the screws.
锁定板在现代骨折手术中已无处不在。最近，制造商开发了具有多轴螺钉功能的锁定板，以优化螺钉的放置。已经证明，非轴向插入单轴锁定螺钉会导致失效时的负荷减弱。我们的假设是，即使是专门为多轴插入设计的植入物，在使用非垂直螺钉时也会出现阻力下降。
测试了四种不同类型（一种单轴和三种多轴锁定板）的现成小片段板。建立了一个生物力学模型来测试螺钉直到失效（定义为断裂和快速损失> 50%的力）。螺钉以 0°、10°和 15°插入。
标准的单轴锁定机制在螺钉以 10°交叉螺纹插入时，力降低了 60%（332N 对 134N）。两个多轴系统的力分别降低了 45%和 34%，相似的显著降低。使用端盖锁定机制的第三个系统显示出高度可变的结果，标准偏差较大。多轴螺钉在 10 度插入角度时平均仅略有减少。
新型锁定板的设计具有吸引人的特性，可在固定过程中提供更多的手术选择。然而，这种自由是以降低力为代价的。我们的结果表明，这些螺钉的安全插入角度更接近 20°，而不是制造商所指示的 30°。此外，各种多轴锁定机制似乎会影响螺钉的整体阻力。
