Simpson D J, Gray H, D'Lima D, Murray D W, Gill H S
Nuffield Department of Orthopaedic Surgery, University of Oxford, Nuffield Orthopaedic Centre, Windmill Road, Oxford OX3 7LD, UK.
Clin Biomech (Bristol). 2008 Nov;23(9):1148-57. doi: 10.1016/j.clinbiomech.2008.06.001. Epub 2008 Jul 18.
Unicompartmental knee replacement offers an effective treatment for patients with single compartment knee disease and is becoming an increasingly popular alternative to total knee replacement. An important cause of failure in a unicompartmental knee replacement implant is polyethylene wear. Significant contributory factors to the amount of polyethylene wear are contact stress, bearing alignment, congruency and thickness.
Four different unicompartmental knee replacement implant designs (Fully-Congruent; Partially-Congruent; Non-Congruent-metal-backed; Non-Congruent-all-polyethylene) were inserted into a validated finite element model of a proximal tibia. The effect that bearing congruency, alignment and thickness had on the polyethylene stresses during a simulated step-up activity for each design was investigated. Additionally, contact pressures were compared to those calculated from Hertz elastic theory.
Only the Fully-Congruent bearing experienced peak von Mises and contact stresses below the lower fatigue limit for polyethylene during the step-up activity. The highest polyethylene contact stresses were observed for the Partially-Congruent and Non-Congruent-metal-backed designs, which experienced approximately three times the polyethylene lower fatigue limit. Increasing the bearing thickness from 3.5mm to 8.5mm of the Non-Congruent design decreased the contact stresses in the bearing; however they did not fall below the lower fatigue limit for polyethylene. Good agreement between finite element and Hertz contact pressures was found.
Fully congruent unicompartmental knee replacement bearings can be markedly thinner without approaching the material failure limit, have a greater potential to preserve bone stock and are less likely to fail mechanically.
单髁膝关节置换为单间室膝关节疾病患者提供了一种有效的治疗方法，并且正日益成为全膝关节置换的一种流行替代方案。单髁膝关节置换植入物失败的一个重要原因是聚乙烯磨损。聚乙烯磨损量的重要促成因素包括接触应力、轴承对线、匹配度和厚度。
将四种不同的单髁膝关节置换植入物设计（完全匹配型；部分匹配型；非匹配金属背衬型；非匹配全聚乙烯型）植入经过验证的胫骨近端有限元模型中。研究了每种设计在模拟上台阶活动期间轴承匹配度、对线和厚度对聚乙烯应力的影响。此外，将接触压力与根据赫兹弹性理论计算得出的压力进行了比较。
在模拟上台阶活动期间，只有完全匹配型轴承的冯·米塞斯峰值应力和接触应力低于聚乙烯的较低疲劳极限。部分匹配型和非匹配金属背衬型设计观察到最高的聚乙烯接触应力，其经历的应力约为聚乙烯较低疲劳极限的三倍。将非匹配型设计的轴承厚度从3.5毫米增加到8.5毫米可降低轴承中的接触应力；然而，它们并未降至聚乙烯的较低疲劳极限以下。有限元压力与赫兹接触压力之间存在良好的一致性。
完全匹配的单髁膝关节置换轴承可以显著更薄而不接近材料失效极限，具有更大的保留骨量的潜力，并且机械失效的可能性更小。
