van Houtem M, Clough R, Khan A, Harrison M, Blunn G W
Centre for Biomedical Engineering, Institute of Orthopaedics and Musculo-Skeletal Science, University College London, Stanmore, UK.
Proc Inst Mech Eng H. 2006 Apr;220(3):449-56. doi: 10.1243/09544119JEIM57.
In vitro testing of total knee replacements (TKRs) is important both at the design stage and after the production of the final components. It can predict long-term in vivo wear of TKRs. The two philosophies for knee testing are to drive the motion by displacement or to drive the motion by force. Both methods have advantages and disadvantages. For force control an accurate simulation of soft tissue restraints is required. This study was devised to assess the accuracy of the soft tissue restraints of the force-controlled Stanmore knee simulator in simulating the restraining forces of the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). In order to do this, human cadaver knee joints were subjected to the ISO Standard Walking Cycle. The resulting kinematics were monitored when the soft tissue structures were intact, when the ACL and PCL were resected, and when they were simulated by springs positioned anteriorly and posteriorly. The stiffness of the springs was determined from the literature. Two different stiffnesses of springs were used which were 7.24 N/mm (designated as soft springs) and 33.8 N/mm (designated as hard springs). All the intact knees showed displacements that were within the range of the machine. Cutting the ACL and PCL resulted in anterior and posterior motion and internal external rotation that were significantly greater than the intact knee. Results showed that when the ACL and PCL were cut hard springs positioned anterior and posterior to the knee returned the knee to near normal anterior-posterior (AP) motion. Using hard springs in the posterior position in any condition reduced rotational displacements. Therefore using springs in a force-controlled simulator is a compromise. More accuracy may be obtained using springs that are of intermediate stiffness.
全膝关节置换术（TKRs）的体外测试在设计阶段和最终部件生产后都很重要。它可以预测TKRs的长期体内磨损情况。膝关节测试的两种理念是通过位移驱动运动或通过力驱动运动。两种方法都有优缺点。对于力控制，需要精确模拟软组织约束。本研究旨在评估力控Stanmore膝关节模拟器的软组织约束在模拟前交叉韧带（ACL）和后交叉韧带（PCL）的约束力量时的准确性。为了做到这一点，对人体尸体膝关节施加ISO标准步行周期。当软组织结构完整时、ACL和PCL被切除时以及它们由前后放置的弹簧模拟时，监测由此产生的运动学情况。弹簧的刚度根据文献确定。使用了两种不同刚度的弹簧，分别为7.24 N/mm（称为软弹簧）和33.8 N/mm（称为硬弹簧）。所有完整的膝关节显示的位移都在机器的范围内。切断ACL和PCL导致前后运动以及内外旋转明显大于完整膝关节。结果表明，当ACL和PCL被切断时，膝关节前后放置的硬弹簧使膝关节恢复到接近正常的前后（AP）运动。在任何情况下，在膝关节后方使用硬弹簧都能减少旋转位移。因此，在力控模拟器中使用弹簧是一种折衷方案。使用中等刚度的弹簧可能会获得更高的准确性。
