Thompson S M, Yohuno D, Bradley W N, Crocombe A D
Chelsea and Westminster NHS Trust, London, UK.
Department of Mechanical Engineering, University of Surrey, Guildford, UK.
Knee Surg Sports Traumatol Arthrosc. 2016 Aug;24(8):2560-6. doi: 10.1007/s00167-015-3923-y. Epub 2015 Dec 22.
The hypothesis of this study is that all-polyethylene (APE) tibial implants offer a biomechanical profile similar to metal-backed tray (MBT). There are significant financial implications, in selected patient groups, if APE can be deemed to perform as well as MBT.
Using a finite element analysis of CAD models provided by DePuy (Leeds), stress distributions were investigated for both an APE and MBT tibial implant. The performance was assessed for cancellous bone at 700 MPa (normal) and at 350 MPa (less stiff). Plots were recorded along the length of the tibia, showing the loads carried by the bone (cortical and cancellous), the implant interface, cement interface and the stem. von Mises stress distributions and percentage volumes were used to assess bone resorption and hence potential for failure (fracture).
Higher stress shielding (resorption) occurred around the keel and stem of the MBT revealing greater potential for bone loss in these areas. APE had no areas of bone resorption (being more flexible resulting in less stress shielding). The stiffer MBT carries a higher proportion of the load down the stem. MBT stress in cancellous bone is lower than APE, as load is distributed to the cortical rim. APE has a marginally favourable strain state in cancellous bone and spreads loads more at the cement interface than MBT.
Modern-day APE bearings may be superior to previously designed implants due to improvements in manufacturing. In the correct patient group, this could offer substantial cost savings.
本研究的假设是全聚乙烯（APE）胫骨植入物具有与金属背衬托盘（MBT）相似的生物力学特征。在特定患者群体中，如果APE被认为与MBT性能相当，将具有重大的经济意义。
利用Depuy（利兹）提供的CAD模型进行有限元分析，研究了APE和MBT胫骨植入物的应力分布。在700兆帕（正常）和350兆帕（刚度较低）下评估松质骨的性能。记录沿胫骨长度的图表，显示骨（皮质骨和松质骨）、植入物界面、骨水泥界面和柄所承受的载荷。采用冯·米塞斯应力分布和体积百分比来评估骨吸收情况，进而评估失效（骨折）的可能性。
MBT的龙骨和柄周围出现了更高的应力屏蔽（吸收），表明这些区域骨丢失的可能性更大。APE没有骨吸收区域（更具柔韧性，导致应力屏蔽较小）。刚度更高的MBT沿柄传递的载荷比例更高。由于载荷分布到皮质边缘，松质骨中的MBT应力低于APE。APE在松质骨中的应变状态略优，并且在骨水泥界面处比MBT更能分散载荷。
由于制造工艺的改进，现代APE轴承可能优于先前设计的植入物。在合适的患者群体中，这可以大幅节省成本。
