Dreyer Michael J, Nasab Seyyed Hamed Hosseini, Favre Philippe, Amstad Fabian, Crockett Rowena, Taylor William R, Weisse Bernhard
Laboratory for Movement Biomechanics, Institute for Biomechanics, ETH Zürich, Gloriastrasse 37/39, 8092, Zurich, Switzerland.
Laboratory for Mechanical Systems Engineering, Empa, Dübendorf, Switzerland.
Biomed Eng Online. 2024 Dec 23;23(1):130. doi: 10.1186/s12938-024-01321-0.
Experimental knee implant wear testing according to ISO 14243 is a standard procedure, but it inherently possesses limitations for preclinical evaluations due to extended testing periods and costly infrastructure. In an effort to overcome these limitations, we hereby develop and experimentally validate a finite-element (FE)-based algorithm, including a novel cross-shear and contact pressure dependent wear and creep model, and apply it towards understanding the sensitivity of wear outcomes to the applied boundary conditions.
Specifically, we investigated the application of in vivo data for level walking from the publicly available "Stan" data set, which contains single representative tibiofemoral loads and kinematics derived from in vivo measurements of six subjects, and compared wear outcomes against those obtained using the ISO standard boundary conditions. To provide validation of the numerical models, this comparison was reproduced experimentally on a six-station knee wear simulator over 5 million cycles, testing the same implant Stan's data was obtained from.
Experimental implementation of Stan's boundary conditions in displacement control resulted in approximately three times higher wear rates (4.4 vs. 1.6 mm per million cycles) and a more anterior wear pattern compared to the ISO standard in force control. While a force-controlled ISO FE model was unable to reproduce the bench test kinematics, and thus wear rate, due to a necessarily simplified representation of the simulator machine, similar but displacement-controlled FE models accurately predicted the laboratory wear tests for both ISO and Stan boundary conditions. The credibility of the in silico wear and creep model was further established per the ASME V&V-40 standard.
The FE wear model is suitable for supporting future patient-specific models and development of novel implant designs. Incorporating the Stan data set alongside ISO boundary conditions emphasized the value of using measured kinematics in displacement control for reliably replicating in vivo joint mechanics in wear simulation. Future work should focus on expanding the range of daily activities simulated and addressing model sensitivity to contact mechanics to further enhance predictive accuracy.
根据ISO 14243进行的实验性膝关节植入物磨损测试是一种标准程序，但由于测试周期长和基础设施成本高，其在临床前评估中存在固有局限性。为了克服这些局限性，我们在此开发并通过实验验证了一种基于有限元（FE）的算法，包括一种新颖的交叉剪切和接触压力相关的磨损和蠕变模型，并将其应用于理解磨损结果对所施加边界条件的敏感性。
具体而言，我们研究了公开可用的“Stan”数据集中的水平行走体内数据的应用，该数据集包含从六名受试者的体内测量得出的单个代表性胫股负荷和运动学，并将磨损结果与使用ISO标准边界条件获得的结果进行比较。为了验证数值模型，在一个六站膝关节磨损模拟器上进行了500万次循环的实验再现，测试了从其获取Stan数据的相同植入物。
与力控制的ISO标准相比，在位移控制下实验实施Stan边界条件导致磨损率大约高出三倍（每百万次循环4.4对1.6毫米），并且磨损模式更靠前。虽然由于模拟器机器的表示必然简化，力控制的ISO有限元模型无法再现台架测试运动学，从而无法再现磨损率，但类似的位移控制有限元模型准确预测了ISO和Stan边界条件下的实验室磨损测试。根据ASME V&V - 40标准进一步确立了计算机模拟磨损和蠕变模型的可信度。
有限元磨损模型适用于支持未来的患者特异性模型和新型植入物设计的开发。将Stan数据集与ISO边界条件结合使用强调了在位移控制中使用测量运动学以在磨损模拟中可靠复制体内关节力学的价值。未来的工作应集中在扩大模拟的日常活动范围以及解决模型对接触力学的敏感性，以进一步提高预测准确性。
