Department of Mechanical and Aerospace EngineeringUniversity of California Los Angeles Los Angeles CA 90095 USA.
David Geffen School of MedicineUniversity of California Los Angeles Los Angeles CA 90095 USA.
IEEE J Transl Eng Health Med. 2024 Feb 12;12:314-327. doi: 10.1109/JTEHM.2024.3365305. eCollection 2024.
The longevity of current joint replacements is limited by aseptic loosening, which is the primary cause of non-infectious failure for hip, knee, and ankle arthroplasty. Aseptic loosening is typically caused either by osteolysis from particulate wear, or by high shear stresses at the bone-implant interface from over-constraint. Our objective was to demonstrate feasibility of a compliant intramedullary stem that eliminates over-constraint without generating particulate wear. The compliant stem is built around a compliant mechanism that permits rotation about a single axis. We first established several models to understand the relationship between mechanism geometry and implant performance under a given angular displacement and compressive load. We then used a neural network to identify a design space of geometries that would support an expected 100-year fatigue life inside the body. We additively manufactured one representative mechanism for each of three anatomic locations, and evaluated these prototypes on a KR-210 robot. The neural network predicts maximum stress and torsional stiffness with 2.69% and 4.08% error respectively, relative to finite element analysis data. We identified feasible design spaces for all three of the anatomic locations. Simulated peak stresses for the three stem prototypes were below the fatigue limit. Benchtop performance of all three prototypes was within design specifications. Our results demonstrate the feasibility of designing patient- and joint-specific compliant stems that address the root causes of aseptic loosening. Guided by these results, we expect the use of compliant intramedullary stems in joint reconstruction technology to increase implant lifetime.
目前关节置换的使用寿命受到无菌性松动的限制，这是髋关节、膝关节和踝关节置换术非感染性失效的主要原因。无菌性松动通常是由颗粒磨损引起的骨溶解，或者是由于骨-植入物界面的高剪切应力导致过度约束引起的。我们的目标是展示一种顺应性髓内干的可行性，这种干可以消除过度约束而不会产生颗粒磨损。顺应性干是围绕着一个允许围绕单个轴旋转的顺应性机构构建的。我们首先建立了几个模型，以了解在给定的角位移和压缩载荷下，机构几何形状与植入物性能之间的关系。然后，我们使用神经网络来确定一个设计空间，其中包含在体内可支持预期 100 年疲劳寿命的几何形状。我们为三个解剖位置中的每一个位置添加制造了一个代表性的机构，并在 KR-210 机器人上对这些原型进行了评估。神经网络对最大应力和扭转刚度的预测误差分别为 2.69%和 4.08%，相对于有限元分析数据。我们确定了所有三个解剖位置的可行设计空间。三个干原型的模拟峰值应力低于疲劳极限。所有三个原型的台架性能都符合设计规格。我们的结果表明，设计针对无菌性松动根本原因的患者和关节特异性顺应性干是可行的。根据这些结果，我们预计在关节重建技术中使用顺应性髓内干将增加植入物的使用寿命。
