Hart Adam, Harvey Edward J, Rabiei Reza, Barthelat Francois, Martineau Paul A
Division of Orthopaedic Surgery, McGill University Health Centre, Montreal, Quebec, Canada.
Department of Mechanical Engineering, McGill University, Montreal, Quebec, Canada.
Med Eng Phys. 2016 Oct;38(10):1037-43. doi: 10.1016/j.medengphy.2016.06.025. Epub 2016 Aug 29.
To promote a quicker return to function, an increasing number of patients are treated with headless screws for acute displaced and even non-displaced scaphoid fractures. Therefore, it is imperative to understand and optimize the biomechanical characteristics of different implants to support the demands of early mobilization. The objective of this study was to evaluate the biomechanical fixation strength of 4 headless compression screws under distracting and bending forces. The Acutrak Standard, Acutrak Mini, Synthes 3.0, and Herbert-Whipple screws were tested using a polyurethane foam scaphoid fracture model. Implants were inserted into the foam blocks across a linear osteotomy. Custom fixtures applied pull-apart and four-point bending forces until implant failure. Pull-apart testing was performed in three different foam densities in order to simulate osteoporotic, osteopenic, and normal bone. The peak pull-apart forces varied significantly between implants and were achieved by (from greatest to least): the Acutrak Standard, Synthes 3.0, Acutrak Mini, and Herbert-Whipple screws. The fully threaded screws (Acutrak) failed at their proximal threads while the shanked screw (Synthes and Herbert Whipple) failed at their distal threads. Similarly, the screws most resistant to bending were (from greatest to least): the Acutrak Standard, Acutrak Mini, Herbert-Whipple, and Synthes. Although the amount of force required for pull-apart failure increased with each increasing simulated bone density (a doubling in density required triple the amount of pull apart force), the mode and sequence of failure was the same. Overall, the fully threaded, conical design of the Acutrak screws demonstrated superior fixation against pull-apart and bending forces than the shanked designs of the Synthes and Herbert-Whipple. We also found a strong relationship between simulated bone density and pull-apart force.
为促进更快恢复功能，越来越多的急性移位甚至无移位舟骨骨折患者接受无头螺钉治疗。因此，了解并优化不同植入物的生物力学特性以满足早期活动的需求至关重要。本研究的目的是评估4种无头加压螺钉在牵张和弯曲力作用下的生物力学固定强度。使用聚氨酯泡沫舟骨骨折模型对Acutrak标准型、Acutrak微型、Synthes 3.0和Herbert-Whipple螺钉进行测试。将植入物通过线性截骨插入泡沫块中。定制夹具施加拉开和四点弯曲力直至植入物失效。为模拟骨质疏松、骨质减少和正常骨，在三种不同泡沫密度下进行拉开测试。不同植入物之间的峰值拉开力差异显著，由大到小依次为：Acutrak标准型、Synthes 3.0、Acutrak微型和Herbert-Whipple螺钉。全螺纹螺钉（Acutrak）在近端螺纹处失效，而带柄螺钉（Synthes和Herbert Whipple）在远端螺纹处失效。同样，最抗弯曲的螺钉由大到小依次为：Acutrak标准型、Acutrak微型、Herbert-Whipple和Synthes。尽管随着模拟骨密度的增加，拉开失效所需的力也增加（密度加倍所需的拉开力增加两倍），但失效模式和顺序相同。总体而言，Acutrak螺钉的全螺纹、锥形设计在抵抗拉开和弯曲力方面比Synthes和Herbert-Whipple的带柄设计表现出更好的固定效果。我们还发现模拟骨密度与拉开力之间存在密切关系。
