肢体不等长为骨科临床中常见的疾病，传统的治疗方式是采用环形外固定支架对骨头进行延长，但是该方法会引发诸多并发症，如针道感染、关节僵硬等。美国NuVasive公司研发的磁力耦合置肢体不等长为骨科临床中常见的疾病，传统的治疗方式是采用环形外固定支架对骨头进行延长，但是该方法会引发诸多并发症，如针道感染、关节僵硬等。美国NuVasive公司研发的磁力耦合置入式肢体延长髓内钉——PRECICE解决了环形外固定支架的弊端，实现了微创肢体延长，同时却也带来新的问题，比如刚度较低、驱动力不足和髓内钉易受腐蚀等等。本文以自主研发置入式肢体延长髓内钉为目标，基于无刷直流电机的驱动原理设计一种包含髓内延长钉和电磁驱动器两个部件的髓内骨延长系统，并开展了以下几个研究工作：制定了髓内骨延长系统的设计指标，提出了步态载荷与静态四点弯曲模型下髓内延长钉的力学性能评价方法。完成了髓内骨延长系统的模型设计后，对髓内延长钉和电磁驱动器进行几何参数的校核，尤其是会影响髓内延长钉牵引力性能的电磁驱动器输出扭矩。采用数值仿真方法对髓内延长钉在步态载荷下的应力场和固有频率进行了计算。结果表明，最大Von-Mises应力是1017.3 MPa，小于钛合金Ti-6Al-4V的屈服强度1100 MPa；固有频率为30.038 Hz，大于人类行走频率1.77±0.36 Hz。此外，参考医药行业标准，对髓内延长钉壳体进行了静态四点弯曲实验，实验结果显示其屈服载荷为1701.71 N，大于PRECICE 2的1446 N。使用ANSYS Maxwell软件对电磁驱动器和髓内延长钉的工作状态进行了电磁仿真，计算结果显示髓内钉放置在驱动器中心处时的输出扭矩是5 mNm。开展了牵引力测试试验，通过自主设计的牵引力测力台测量了髓内延长钉在正常工作状态下的牵引力，试验结果表明髓内骨延长系统能够提供的最大牵引力可达800 N。对髓内骨延长系统开展了多目标多约束优化，借助骨骼动力学和变径圆管悬臂梁模型以求解壳体的Von-Mises应力；采用无刷直流电机模型验算了电磁驱动器的输出扭矩。将上述两种模型进行联立构建以输出扭矩为目标，驱动器几何尺寸为约束的函数，并代入遗传算法内求得最优解。结果表明，电磁驱动器的输出扭矩提升4.76%，总重和功耗分别降低58.39%和92.48%。本论文提出了一种髓内骨延长系统的设计方法和系统刚度与驱动的优化方法，为植入式肢体延长髓内钉的国产化提供了技术方案和理论基础，具有重要的医学意义和社会意义。
Leg length discrepancy is a common orthopedic disease. The conventional treatment method uses an Ilizarov external fixator to lengthen the bone, which will cause inconvenience and severe complications such as pin tract infection and ankylosis. On the other hand, the magnetically implantable lengthening nail, PRECICE, invented by Nuvasive, shows magnificent results. However, it will bring new problems, such as low stiffness, insufficient driving force, and corrosion of lengthening nails. In this thesis, based on the demand for independent research and development of implantable lengthening nails, research of novel design of implantable lengthening nail and its driver based on brushless DC motor is carried out from the following aspects:Research is carried out to formulate the design guidelines for an implantable bone lengthening system, including the reference values of the load applied on the implantable lengthening nail under the gait-load model and static four-point bending model. After completing the model design of the implantable bone lengthening system, it is necessary to check the geometric parameters of the implantable lengthening nail and the electromagnetic driver, especially the output torque of the electromagnetic driver that affects its distraction performance.Then, the stress value and the natural frequency of the implantable lengthening nail were calculated using numerical analysis. The results show that the maximum Von-Mises stress is 1017.3 MPa, less than the yield strength of titanium alloy, Ti-6Al-4V, which is 1100 MPa; the natural frequency is 30.038 Hz, which is higher than the human walking frequency of 1.77±0.36 Hz. In addition, a static four-point bending test is performed on the protective shell of the implantable lengthening nail after referring to the standard. The experimental results show that the yield load of the shell is 1701.71 N, which is greater than PRECICE 2 of 1446 N.Regarding the electromagnetic driver and implantable lengthening nail working state, ANSYS Maxwell is utilized, and the result shows that the output torque at the center is 5 mNm. A self-designed distraction force test bench measures the implantable bone lengthening system distraction force under normal working circumstances. The test result shows that the maximum distraction force provided by the system is 800 N.Lastly, the constrained multi-objective optimization of the implantable bone lengthening system is conducted. Von-Mises stress of the protective shell is verified using bone dynamics and a cantilever beam model. At the same time, the electromagnetic driver‘s output torque is established using a brushless DC motor model. Both models are constructed simultaneously with the output torque and total weight as an objective. At the same time, the geometric size of the electromagnetic driver is substituted into the genetic algorithm as a constraint to obtain the optimal solution. The results show that the output torque of the electromagnetic driver is increased by 4.76%, and the total weight and power consumption are reduced by 58.39% and 92.48%, respectively.Overall, this thesis proposed a design method for an implantable bone lengthening system and an optimization method to improve system performance, which provides a technical solution and theoretical basis for implantable lengthening nails that is significant for medical and social.
