Perrault Frederique D, Aubin Carl-Eric, Wang Xiaoyu, Schwend Richard M
École Polytechnique de Montréal, Montréal, Canada.
Stud Health Technol Inform. 2012;176:307-10.
Iliac screws used in long instrumentation for deformity treatment are subject to large forces, which may sometimes lead to fixation failures (intra- and postoperatively). The objective of this study was to analyze the biomechanics of iliac screw fixations. The study was based on a patient-specific simulation of a neuromuscular scoliosis case with a long instrumentation to the pelvis. A multi body flexible model was created using a preoperative 3D reconstructed spine and pelvis. The side bending radiographs were used to personalize the mechanical properties. The instrumentation construct was modeled as rigid bodies and flexible beams connected by kinematic joints. Three instrumentation parameters were studied: the connector length, the inter rod connectors and the use of sacral screws. The simulations showed that the forces and torques at the iliac screws were lowered by 9% and 25% respectively by reducing the lateral connector length (from 20 to 10 mm). An inter rod connector did not significantly reduce the iliac screw loads. Sacral screws reduced the functional loads on the iliac screws, but hardware related problems may be shifted onto the sacral screws. Sacral screws in conjunction with inter rod connectors reduced the loads at iliac screws without overloading the sacral screws. The preliminary results showed that the forces at the iliac screws could be lowered through different instrumentation parameters. In the next step of the study, the model validation will be further completed and used to evaluate other instrumentation factors by means of an experimental design framework. The knowledge of loading biomechanics at the iliac screw fixation is important for finding solutions to reduce the risk of failure, such as improving preoperative planning, instrumentation techniques and iliac screw construct design.
用于畸形治疗的长节段内固定中使用的髂骨螺钉承受较大的力，这有时可能导致固定失败（术中及术后）。本研究的目的是分析髂骨螺钉固定的生物力学。该研究基于对一例神经肌肉型脊柱侧弯病例的患者特异性模拟，该病例采用长节段内固定至骨盆。使用术前三维重建的脊柱和骨盆创建了一个多体柔性模型。利用侧弯X线片来个性化力学性能。将内固定结构建模为通过运动关节连接的刚体和柔性梁。研究了三个内固定参数：连接器长度、棒间连接器以及骶骨螺钉的使用。模拟结果表明，将横向连接器长度从20毫米减少到10毫米，可使髂骨螺钉处的力和扭矩分别降低9%和25%。棒间连接器并未显著降低髂骨螺钉的负荷。骶骨螺钉减少了髂骨螺钉上的功能负荷，但与硬件相关的问题可能会转移到骶骨螺钉上。骶骨螺钉与棒间连接器结合使用可降低髂骨螺钉处的负荷，而不会使骶骨螺钉过载。初步结果表明，通过不同的内固定参数可降低髂骨螺钉处的力。在研究的下一步，将进一步完成模型验证，并通过实验设计框架用于评估其他内固定因素。了解髂骨螺钉固定处的加载生物力学对于找到降低失败风险的解决方案很重要，例如改进术前规划、内固定技术和髂骨螺钉结构设计。
