新型微创椎弓根钉-板固定系统的生物力学测试

Biomechanical study of a novel minimally-invasive pedicle screw-plate system

中文关键词:  腰椎  椎间融合术  微创  椎弓根螺钉  生物力学

英文关键词:Lumbar spine  Interbody fusion  Minimally invasive surgery  Pedicle screw  Biomechanics

中文摘要:

  【摘要】 目的：评估新型微创椎弓根钉-板内固定系统的生物力学强度。方法：根据美国材料测试协会（ASTM）标准构建单钉-棒测试组件，在万能材料试验机上分别对微创椎弓根钉-板、单向椎弓根钉-棒和万向椎弓根钉-棒组件进行生物力学强度测试。测试内容包括静态侧压测试和疲劳测试。在静态侧压测试中使用6套组件，记录组件屈服载荷、屈曲刚度以及失效模式。在疲劳测试中记录完成250万次循环负荷的最大应力数值。结果：微创椎弓根钉-板组件的屈服载荷和屈曲刚度显著低于单向椎弓根钉-棒组件（834.6±74.5N vs 1087.7±59.0N，218.1±22.4N vs 300.0±14.9N，P<0.001）。微创椎弓根钉板组件的屈服载荷与万向椎弓根钉-棒组件比较无显著性差异（834.6±74.5N vs 762.8±88.6N，P=0.118）；而钉-板组件的刚度显著低于万向钉-棒组件（218.1±22.4N/mm vs 389.5±37.2N/mm，P<0.001）。单向椎弓根钉-棒组件的失败模式为连接棒发生塑性形变，万向椎弓根钉-棒组件为“球窝偶联”结构失效，微创椎弓根钉-板组件为钛板的塑性形变和钉-板连接部位失效。在250万次动态侧压疲劳测试中，单向椎弓根钉-棒组件、微创椎弓根钉-板组件和万向椎弓根钉-棒组件分别在450N、450N和350N循环载荷下完成测试。结论：新型微创椎弓根钉-板内固定系统可耐受250万次450N循环载荷作用，同时具有高屈服载荷和低屈曲刚度的特点。

英文摘要:

  【Abstract】 Objectives: To evaluate the biomechanical strength of the novel minimally-invasive pedicle screw-plate system. Methods: Single screw-rod test model was developed according to a standard for destructive mechanical test published by the American Society for Testing Materials. Minimally-invasive pedicle screw-plate assembles, monoaxial pedicle screw-rod assembles and polyaxial pedicle screw-rod assembles were tested on universal material testing machine for biomechanical study. The tests included static compression bending test and fatigue test. 6 assembles of each group were tested in static test and the yield load, the bending stiffness and modes of failure were recorded. Modes of failure and maximum run out load enduring 2.5×106 cycles were reported in fatigue test. Results: The yield load and bending stiffness of the minimally-invasive pedicle screw-plate assembles were significantly less than those of the monoaxial pedicle screw-rod assembles(834.6±74.5N vs 1087.7±59.0N, 218.1±22.4N vs 300.0±14.9N, P<0.001). The yield load of the minimally-invasive pedicle screw-plate assembles was not significantly larger than that of the polyaxial pedicle screw-rod assembles(834.6±74.5N vs 762.8±88.6N, P=0.118), while the bending stiffness was significantly less than that of the other(218.1±22.4N/mm vs 389.5±37.2N/mm, P<0.001). Failure modes in monoaxial pedicle screw-rod assembles were rod plastic deformation, while the failure modes in polyaxial pedicle screw-rod assembles were loosening of the ball-in-cup mechanism． Failure modes in minimally-invasive pedicle screw-plate assembles included the plastic deformation at the plate or the plate-screw connection part. Run out load enduring 2.5×106 cycles was 450N, 450N and 350N for minimally-invasive pedicle screw-plate assembles, monoaxial pedicle screw-rod assembles and polyaxial pedicle screw-rod assembles respectively. Conclusions: The novel minimally-invasive pedicle screw-plate system has high yield strength and low construct stiffness, which can afford 450N load within 2.5×106 cycles.