Osseointegrated transfemoral prostheses experience aseptic complications with an incidence between 3% and 30%. The main aseptic risks are implant loosening, adverse bone remodeling, and post-operative periprosthetic fractures. Implant loosening can either be due to a lack of initial (primary) stability of the implant, which hinders bone ingrowth and therefore prevents secondary stability, or, in the long-term, to the progressive resorption of the periprosthetic bone. Post-operative periprosthetic fractures are most often caused by stress concentrations. A method to simultaneously evaluate the primary stability and the load transfer is currently missing. Furthermore, the measurement errors are seldom reported in the literature. In this study a method to reliably quantify the bone implant interaction of osseointegrated transfemoral prostheses in terms of primary stability and load transfer was developed, and its precision was quantified. Micromotions between the prosthesis and the host bone and the strains on the cortical bone were measured on five human cadaveric femurs with a typical commercial osseointegrated implant. To detect the primary stability of the implant and the load transfer, cyclic loads were applied, simulating the peak load during gait. Digital Image Correlation was used to measure displacements and bone strains simultaneously throughout the test. Permanent migrations and inducible micromotions were measured (three translations and three rotations), while, on the same specimen, the full-field strain distribution on the bone surface was measured. The repeatability tests showed that the devised method had an intra-specimen variability smaller than 6 μm for the translation, 0.02 degrees for the rotations, and smaller than 60 microstrain for the strain distribution. The inter-specimen variability was larger than the intra-specimen variability due to the natural differences between femurs. Altogether, the measurement uncertainties (intrinsic measurement errors, intra-specimen repeatability and inter-specimen variability) were smaller than critical levels of biomarkers for adverse remodelling and aseptic loosening, thus allowing to discriminate between stable and unstable implants, and to detect critical strain magnitudes in the host bone. In conclusion, this work showed that it is possible to measure the primary stability and the load transfer of an osseointegrated transfemoral prosthesis in a reliable way using a combination of mechanical testing and DIC.

中文翻译：

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用于评估骨整合植入经股假体的初步稳定性和负载转移的可靠体外方法

骨整合经股骨假体会出现无菌并发症，发生率在 3% 至 30% 之间。主要的无菌风险是种植体松动、骨重塑不良和术后假体周围骨折。种植体松动可能是由于种植体缺乏初始（初级）稳定性，这阻碍了骨向内生长，从而阻碍了二次稳定性，或者从长远来看，是由于假体周围骨的逐渐吸收。术后假体周围骨折最常由应力集中引起。目前缺少同时评估初级稳定性和荷载传递的方法。此外，文献中很少报道测量误差。在这项研究中，开发了一种在初级稳定性和负荷转移方面可靠地量化骨整合经股假体的骨植入相互作用的方法，并量化了其精度。使用典型的商业骨整合植入物，在五个人体股骨上测量了假体和宿主骨之间的微运动以及皮质骨上的应变。为了检测植入物的主要稳定性和负载转移，施加循环负载，模拟步态期间的峰值负载。数字图像相关用于在整个测试过程中同时测量位移和骨应变。测量永久迁移和诱导微运动（三个平移和三个旋转），同时在同一样本上测量骨表面的全场应变分布。重复性测试表明，所设计的方法的样本内平移变异性小于 6 μm，旋转变异性小于 0.02 度，应变分布变异性小于 60 微应变。由于股骨之间的自然差异，样本间变异性大于样本内变异性。总而言之，测量不确定性（固有测量误差、样本内重复性和样本间变异性）小于不良重塑和无菌性松动的生物标志物的临界水平，从而可以区分稳定和不稳定的种植体，并检测临界应变大小在宿主骨骼中。总之，这项工作表明，结合机械测试和 DIC，可以可靠地测量骨整合经股骨假体的初级稳定性和负载转移。