Biomechanics and Implant Technology Research Laboratory, Department of Orthopaedics, Rostock University Medical Center, Doberaner Straße 142, 18057, Rostock, Germany.
Institute of Structural Mechanics, University of Rostock, Germany.
J Mech Behav Biomed Mater. 2021 Jan;113:104115. doi: 10.1016/j.jmbbm.2020.104115. Epub 2020 Sep 28.
Femoral bone loss due to stress and strain shielding is a common problem in hip resurfacing arthroplasty (HRA), which arises from the different stiffness of implant materials and the adjacent bone. Usually, the implants used in HRA are made of cobalt-chromium alloy (CoCr). As a novel concept, implants may also be made of ceramics, whose stiffness exceeds that of the adjacent bone by a multiple. Therefore, this computational study aimed to evaluate whether poly (ether-ether-ketone) (PEEK) or a hybrid material with a PEEK body and ceramic surface made of alumina toughened zirconia (ATZ) might be more suitable implant alternatives for HRA, as they can avoid stress and strain shielding. A reconstructed model of a human femur with an HRA implant was simulated, whereby the material of the HRA was varied between CoCr, ATZ, zirconia toughened alumina (ZTA), PEEK, and a hybrid PEEK-ATZ material. The implant fixation method also varied (cemented or cementless). The simulated models were compared with an intact model to analyze stress and strain distribution in the femoral head and neck. The strain distribution was evaluated at a total of 30,344 (cemented HRA) and 63,531 (uncemented HRA) nodes in the femoral head and neck region and divided into different strain regions (<400 µm/m: atrophy; 400-3000 μm/m: bone preserving and building; 3000-20,000 μm/m: yielding and >20,000 μm/m fracture). In addition, the mechanical stability of the implants was evaluated. When the material of the HRA implant was simulated as metal or ceramic while evaluating the strains, it was seen that around 22-26% of the analyzed nodes in the femoral head and neck were in an atrophic region, 47-51% were in a preserving or building region, and 27-28% were in a yielding region. In the case of PEEK implant, less than 0.5% of the analyzed nodes were in an atrophic region, 66-69% in a preserving or building region, and 31-34% in a yielding region. The fixation technique also had a small influence. When a hybrid HRA was simulated, the strains at the analyzed nodes depended on the thickness of the ceramic material. In conclusion, the material of the HRA implant was crucial in terms of stress and strain distribution in the adjacent bone. HRA made of PEEK or a hybrid material leads to decisively reduced stress and strain alteration compared to stiffer materials such as CoCr, ATZ, and ZTA. This confirms the potential for reduction in stress and strain shielding in the femoral head with the use of a hybrid material with a PEEK body for HRA.
由于应力和应变屏蔽导致的股骨骨丢失是髋关节表面置换术（HRA）的一个常见问题，这是由于植入物材料和相邻骨骼的不同刚度引起的。通常，HRA 中使用的植入物由钴铬合金（CoCr）制成。作为一个新概念，植入物也可以由陶瓷制成，其刚度是相邻骨骼的数倍。因此，这项计算研究旨在评估聚醚醚酮（PEEK）或具有 PEEK 本体和氧化铝增韧氧化锆（ATZ）陶瓷表面的混合材料是否可能成为 HRA 更合适的植入物替代物，因为它们可以避免应力和应变屏蔽。模拟了带有 HRA 植入物的人股骨的重建模型，其中 HRA 的材料在 CoCr、ATZ、氧化锆增韧氧化铝（ZTA）、PEEK 和 PEEK-ATZ 混合材料之间变化。植入物固定方法也有所不同（水泥固定或非水泥固定）。将模拟模型与完整模型进行比较，以分析股骨头和颈部的应力和应变分布。在股骨头和颈部区域的总共 30344 个（水泥固定 HRA）和 63531 个节点（非水泥固定 HRA）上评估应变分布，并将其分为不同的应变区域（<400 μm/m：萎缩；400-3000 μm/m：保骨和建骨；3000-20000 μm/m：屈服；>20000 μm/m：骨折）。此外，还评估了植入物的机械稳定性。当模拟 HRA 植入物的材料为金属或陶瓷时，评估应变时可以看到，股骨头和颈部约有 22-26%的分析节点处于萎缩区域，47-51%处于保骨和建骨区域，27-28%处于屈服区域。在 PEEK 植入物的情况下，小于 0.5%的分析节点处于萎缩区域，66-69%处于保骨和建骨区域，31-34%处于屈服区域。固定技术也有很小的影响。当模拟混合 HRA 时，分析节点的应变取决于陶瓷材料的厚度。总之，HRA 植入物的材料对于相邻骨骼中的应力和应变分布至关重要。与 CoCr、ATZ 和 ZTA 等更硬的材料相比，PEEK 或混合材料制成的 HRA 可显著降低应力和应变变化。这证实了使用 PEEK 本体和混合材料制造的混合材料在 HRA 中可减少股骨头的应力和应变屏蔽。
