Yu Tzai-Chiu, Huang Chang-Hung, Hsieh Chia-Hsun, Liau Jiann-Jong, Huang Chun-Hsiung, Cheng Cheng-Kung
Department of Orthopaedic Surgery, Buddhist Tzu Chi General Hospital, Hualien, Taiwan.
Clin Biomech (Bristol). 2006 Feb;21(2):147-51. doi: 10.1016/j.clinbiomech.2005.08.009. Epub 2005 Oct 24.
Tibial baseplates were occasionally reported with clinical fatigue failures. This study postulated that tibial baseplate of a specific mobile bearing design with a uniform thickness across the baseplate offers more fatigue resistance than the fixed-bearing design. Tibial baseplates of a fixed bearing and a mobile bearing design were fatigue-tested in vitro to study their fatigue resistance.
Five samples of each design were tested under a sinusoidal loading between 90 N and 900 N at 30 Hz till failure or 10 million cycles. Experimental setup followed a standard published test method. Scanning electron microscope was used for inspecting the fracture surface of the failed baseplate.
Two baseplates of fixed bearing design failed before 10 million cycles. Fatigue crack advancement marks were visible on the fractured surface of the failed samples. The fractured cross-section showed that the failure started near the end of the fin, it was likely due to the stress concentration as stress singularity existed at a point of sudden geometrical change. Five mobile bearing baseplates passed the test. Design of the tibial baseplate without fin structure and with a uniform thickness across the whole baseplate could help reducing the incidence of fatigue failure.
The prosthesis survival rate was influenced by the long-term integrity of the metallic part of the prostheses such as the tibial baseplate. This study revealed that the tibial baseplate of a mobile bearing design with a uniform thickness provided better fatigue resistance than fixed bearing one. Standardized fatigue screening of the tibial baseplate was considered important in designing knee prostheses.
胫骨基板偶尔会出现临床疲劳失效的情况。本研究推测，一种特定的活动轴承设计且整个基板厚度均匀的胫骨基板比固定轴承设计具有更高的抗疲劳性。对固定轴承和活动轴承设计的胫骨基板进行体外疲劳测试，以研究它们的抗疲劳性。
每种设计的五个样本在90牛至900牛的正弦载荷、30赫兹频率下进行测试，直至失效或达到1000万次循环。实验装置遵循已发表的标准测试方法。使用扫描电子显微镜检查失效基板的断裂表面。
两个固定轴承设计的基板在1000万次循环前失效。在失效样本的断裂表面可见疲劳裂纹扩展痕迹。断裂横截面显示，失效始于鳍片末端附近，这可能是由于在几何形状突然变化的点存在应力奇异性导致应力集中。五个活动轴承基板通过了测试。无鳍片结构且整个基板厚度均匀的胫骨基板设计有助于降低疲劳失效的发生率。
假体的存活率受假体金属部件（如胫骨基板）的长期完整性影响。本研究表明，厚度均匀的活动轴承设计的胫骨基板比固定轴承设计的具有更好的抗疲劳性。在膝关节假体设计中，对胫骨基板进行标准化的疲劳筛选被认为很重要。
