Campbell David, Lewis Peter, Mooney Luke
Wakefield Orthopaedic Clinic, Adelaide, Australia; University of Adelaide, Adelaide, Australia.
Wakefield Orthopaedic Clinic, Adelaide, Australia.
Knee. 2020 Jun;27(3):987-992. doi: 10.1016/j.knee.2020.02.005. Epub 2020 Feb 18.
A biconcave polyethylene (PE) bearing was developed for mobile-bearing unicompartmental knee arthroplasties (UKA) to reduce PE dislocation.
A modification of the BalanSys Unicompartmental knee system with a biconcave PE and convex tibial component was used in 32 prostheses in 28 patients. Clinical outcomes and five cases of PE fracture are reported and extensively analyzed ex vivo.
Visual Analogue Score of pain and satisfaction, and Knee Society Scores improved for all patients. The passive range of motion was 130°. No PE bearings dislocated. Five bearings fractured with oxidation, cracking and delamination at the thinnest central region of the PE. The combination of increased stress and decreased poly thickness was associated with increased creep. PE oxidation caused embrittlement and contributed to fractures in the thin waist of the implant.
The unforeseen consequence of a novel design of a UKA that resulted in a specific mechanical and tribological mode of failure is reported. We conclude the PE failed due to a biconcave design that increased stress on the implant at its region of risk combined with a decrease of the polyethylene thickness by 1 mm in the central area.
为活动平台单髁膝关节置换术（UKA）研发了一种双凹面聚乙烯（PE）关节面，以减少PE脱位。
对BalanSys单髁膝关节系统进行改良，采用双凹面PE和凸形胫骨部件，应用于28例患者的32个假体。报告临床结果，并对5例PE骨折进行体外广泛分析。
所有患者的视觉模拟疼痛评分和满意度评分以及膝关节协会评分均有所改善。被动活动范围为130°。未发生PE关节面脱位。5个关节面在PE最薄的中央区域发生氧化、开裂和分层而骨折。应力增加和聚乙烯厚度减小共同导致蠕变增加。PE氧化导致脆化，并促使植入物薄腰部发生骨折。
报道了一种UKA新颖设计产生的意外后果，该设计导致了一种特定的机械和摩擦学失效模式。我们得出结论，PE的失效是由于双凹面设计增加了植入物危险区域的应力，同时中央区域聚乙烯厚度减少了1毫米。
