Ansari Farzana, Lee Taylor, Malito Louis, Martin Audrey, Gunther Stephen B, Harmsen Samuel, Norris Tom R, Ries Mike, Van Citters Douglas, Pruitt Lisa
Department of Mechanical Engineering, University of California, Berkeley, CA, USA.
Department of Mechanical Engineering, University of California, Berkeley, CA, USA.
J Shoulder Elbow Surg. 2016 Jul;25(7):1041-50. doi: 10.1016/j.jse.2015.10.017. Epub 2016 Jan 14.
The longevity of total shoulder replacement is primarily limited by the performance of the ultrahigh-molecular-weight polyethylene (UHMWPE) glenoid component in vivo. Variations in glenoid design (conformity, thickness), biomechanics (joint kinematics), and UHMWPE material selection (sterilization, cross-linking) distinguish total shoulder replacements from hip and knee arthroplasty devices. These variables can lead to severe mechanical failures, including gross fracture.
Sixteen retrieved glenoids with severe fracture were analyzed. The explant cohort included 3 material groups (gamma-sterilized Hylamer; gamma-sterilized UHMWPE; and gas plasma-sterilized, remelted, highly cross-linked UHMWPE [HXL]) and a range of conformities (0- to 10-mm radial mismatch). Analysis included fractography (optical and scanning electron microscopy) and Fourier transform infrared spectroscopy for oxidative analysis.
Fracture primarily occurred along the exterior rim for all 16 explants. Fourier transform infrared analysis and fractography revealed significant oxidative embrittlement for all gamma-sterilized glenoids. Fatigue striations and internal flaws were evident on the fracture surface of the HXL glenoid, with little oxidation detected.
Fracture initiated at the external rim of all devices. Elevated oxidation levels and visible material distortion for representative gamma-sterilized conventional and Hylamer devices suggest oxidative embrittlement as a driving force for crack inception and subsequent fracture. Brittle fracture of theHXL glenoid resulted from a combination of elevated contact stress due to a nonconforming surface, an internal flaw, and reduced resistance to fatigue crack growth. This demonstrates that glenoid fracture associated with oxidation has not been eliminated with the advent of modern materials (HXL) in the shoulder domain.
Basic Science Study; Implant Retrieval Study.
全肩关节置换术的使用寿命主要受体内超高分子量聚乙烯（UHMWPE）关节盂部件性能的限制。关节盂设计（贴合度、厚度）、生物力学（关节运动学）以及UHMWPE材料选择（灭菌、交联）方面的差异，使全肩关节置换术有别于髋关节和膝关节置换装置。这些变量可能导致严重的机械故障，包括严重骨折。
对16个取出的严重骨折的关节盂进行分析。植入物队列包括3种材料组（γ射线灭菌的Hylamer；γ射线灭菌的UHMWPE；以及气体等离子体灭菌、重熔、高度交联的UHMWPE [HXL]）和一系列贴合度（0至10毫米的径向不匹配）。分析包括断口分析（光学和扫描电子显微镜）以及用于氧化分析的傅里叶变换红外光谱。
所有16个取出的植入物的骨折主要发生在外部边缘。傅里叶变换红外分析和断口分析显示，所有γ射线灭菌的关节盂都有明显的氧化脆化。HXL关节盂的断口表面有明显的疲劳条纹和内部缺陷，检测到的氧化很少。
所有装置的骨折均始于外部边缘。代表性的γ射线灭菌的传统装置和Hylamer装置氧化水平升高和可见的材料变形表明，氧化脆化是裂纹起始和随后骨折的驱动力。HXL关节盂的脆性骨折是由于表面不匹配导致接触应力升高、内部缺陷以及抗疲劳裂纹扩展能力降低共同作用的结果。这表明，随着肩部领域现代材料（HXL）的出现，与氧化相关的关节盂骨折并未消除。
基础科学研究；植入物取出研究。
