Benson L C, DesJardins J D, Harman M K, LaBerge M
Department of Bioengineering, Clemson University, Clemson, South Carolina 29634-0905, USA
Proc Inst Mech Eng H. 2002;216(6):409-18. doi: 10.1243/095441102321032201.
A loading protocol approximating forces, torques and motions at the knee during stair descent was developed from previously published data for input into a force-controlled knee simulator. A set of total knee replacements (TKRs) was subjected to standard walking cycles and stair descent cycles at a ratio of 70: 1 for 5 million cycles. Another set of implants with similar articular geometry and the same ultra-high molecular weight polyethylene (UHMWPE) resin (GUR 415), sterilization and packaging was tested with standard walking cycles only. Implant kinematics, gravimetric wear and surface roughness of the UHMWPE inserts were analysed for both sets of implants. Contact stresses were calculated for both loading protocols using a Hertzian line contact model. Significantly greater weight loss (p < 0.05) and more severe surface damage of UHMWPE inserts resulted with the walking + stair descent loading protocol compared to walking cycles only. Anterior-posterior (AP) tibiofemoral contact point displacements were lower during stair descent than walking, but not significantly different (p = 0.05). Contact stresses were significantly higher during stair descent than walking, owing to higher axial loads and the smaller radius of curvature of the femoral components at higher flexion angles. High contact stresses on UHMWPE components are likely to accelerate the fatigue of the material, resulting in more severe wear, similar to what is observed in retrieved implants. Thus the inclusion of loading protocols for activities of daily living in addition to walking is warranted for more realistic in vitro testing of TKRs.
根据先前发表的数据，制定了一种近似下楼梯时膝关节受力、扭矩和运动的加载方案，用于输入力控膝关节模拟器。一组全膝关节置换术（TKR）以70:1的比例进行标准步行周期和下楼梯周期运动，共500万次循环。另一组具有相似关节几何形状、相同超高分子量聚乙烯（UHMWPE）树脂（GUR 415）、经过相同灭菌和包装处理的植入物仅进行标准步行周期测试。对两组植入物的植入物运动学、UHMWPE衬垫的重量磨损和表面粗糙度进行了分析。使用赫兹线接触模型计算了两种加载方案下的接触应力。与仅进行步行周期相比，步行+下楼梯加载方案导致UHMWPE衬垫的重量损失显著更大（p < 0.05），表面损伤更严重。下楼梯过程中胫股前后（AP）接触点位移低于步行时，但差异不显著（p = 0.05）。下楼梯时的接触应力显著高于步行时，这是由于更高的轴向载荷以及在更高屈曲角度时股骨部件的曲率半径更小。UHMWPE部件上的高接触应力可能会加速材料的疲劳，导致更严重的磨损，这与在取出的植入物中观察到的情况类似。因此，除了步行外，纳入日常生活活动的加载方案对于更现实的TKR体外测试是必要的。
