Background

Coated implant components for total knee arthroplasties are primarily used for metal-sensitive patients and are offered by different manufacturers. However, there is only little knowledge with respect to their coating design and supposed superior tribological performance. Our aim was to compare retrieved coated implants by identifying present damages, critical factors influencing the coating durability and their correlation to the clinical performance.

Materials and methods

28 retrieved knee endoprostheses from nine different manufacturers were analyzed for potential surface defects as well as the coating strategy for each manufacturer. The coating designs were investigated on preserved regions with regard to substrate and coating material, layer thickness and roughness using scanning electron microscopy and confocal microscopy. Furthermore, the mechanical properties and adhesive strength of the layer were evaluated by nanoindentation and scratch testing. The friction performance of the coatings against ultra-high molecular weight polyethylene (UHMWPE) was investigated in a tribological test. In addition, clinical data were collected and evaluated for all patients.

Results

Our cohort of 28 retrieved knee endoprostheses exhibited different damage patterns in the articulating area with an incidence of 79% for discoloration and 21% for coating delamination. All coatings presented droplets, macropores and pinholes in preserved areas, which can be attributed to the coating and post-polishing processes. Interestingly, the adhesive strength was significantly increased by 60.4% for titanium nitride coatings on TiAl6V4 alloy in comparison to CoCr28Mo6 substrates. The friction behavior of titanium nitride coatings against UHMWPE is similar to uncoated CoCr28Mo6 alloy and lowest for the ZrN multi-layer coating with a reduction of 14%.

Discussion

This study shows that manufacturing related coating deposition defects can cause wear due to adhesive failure and corrosion underneath the coating layers. Adhesive strength was identified as a critical factor for coating durability. Minor adhesive strength was present on CoCr28Mo6 cast alloy in comparison to good adhesion of Ti-based coatings on TiAl6V4 wrought alloy. Based on our findings, this is consistent to higher prevalence rates of CoCr28Mo6/TiNbN coatings for gross delamination and pitting damage with increasing implantation time.

中文翻译：

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TiAl6V4 和 CoCr28Mo6 上市售膝关节植入物涂层 TiN、TiNbN 和 ZrN 的检索研究。

背景

用于全膝关节置换术的涂层植入部件主要用于金属敏感患者，由不同制造商提供。然而，人们对其涂层设计和假定的卓越摩擦学性能知之甚少。我们的目的是通过识别当前的损伤、影响涂层耐久性的关键因素及其与临床表现的相关性来比较回收的涂层种植体。

材料和方法

对来自 9 个不同制造商的 28 个膝关节内假体进行了分析，以了解潜在的表面缺陷以及每个制造商的涂层策略。使用扫描电子显微镜和共焦显微镜对保留区域的基材和涂层材料、层厚度和粗糙度进行了涂层设计的研究。此外，通过纳米压痕和划痕测试评估了该层的机械性能和粘合强度。通过摩擦学测试研究了涂层与超高分子量聚乙烯 (UHMWPE) 的摩擦性能。此外，还收集并评估了所有患者的临床数据。

结果

我们的队列中回收的 28 个膝关节内置假体在关节区域表现出不同的损伤模式，变色发生率为 79%，涂层分层发生率为 21%。所有涂层在保留区域均呈现液滴、大孔和针孔，这可归因于涂层和后抛光过程。有趣的是，与 CoCr28Mo6 基材相比，TiAl6V4 合金上氮化钛涂层的附着强度显着提高了 60.4%。氮化钛涂层与 UHMWPE 的摩擦行为与未涂层的 CoCr28Mo6 合金相似，ZrN 多层涂层的摩擦行为最低，降低了 14%。

讨论

这项研究表明，与制造相关的涂层沉积缺陷可能会因涂层下方的粘合失效和腐蚀而导致磨损。粘合强度被认为是涂层耐久性的关键因素。与 TiAl6V4 变形合金上的钛基涂层良好的附着力相比，CoCr28Mo6 铸造合金上的附着力较小。根据我们的研究结果，这与 CoCr28Mo6/TiNbN 涂层随着植入时间的增加而出现严重分层和点蚀损坏的发生率较高是一致的。