【国外标准】 Standard Test Method for Fatigue Testing of Total Knee Femoral Components Under Closing Conditions

5.1 Clinical fractures of total knee femoral components have been observed and reported in the literature (1-12).4 (See X1.4.)5.2 This test method provides a procedure to perform fatigue testing on total knee femoral components under closing conditions caused by an unsupported condyle that result in a tensile stress on the articular surface and a compressive stress on the interior, beveled surfaces.5.3 This test method is intended to evaluate the fatigue performance of knee femoral components under a simulated articulation loading condition. The load acts to move the posterior femoral condyle toward the anterior flange.5.4 This test method simulates a clinically severe condition in which all bony support is lost and one condyle is supporting the complete load at the knee joint at 90° of tibiofemoral flexion.5.5 Testing in accordance with this test method typically produces regions of high tensile stress in the intercondylar notch and on the articular surface where the anterior flange transitions to condyle.5.6 The loading of total knee femoral components using this test method may differ from actual in vivo loading conditions. The results obtained here cannot be used to directly predict in vivo performance. However, this test method is designed to enable comparison between the fatigue performance of different total knee femoral component designs when tested under similar closing conditions.1.1 This standard applies to metallic total knee femoral components used in total knee arthroplasty (TKA). Femoral components made of nonmetallic materials (for example, ceramic, polymer) could possibly be evaluated using this test method. However, such materials may include risks of new failure mechanisms which are not considered in this test method.1.2 The procedure described in this standard is performed on total knee femoral components for supporting determination of fatigue behavior under closing-style loading conditions. Closing-style loading refers to forces that act to reduce the femoral intercondylar depth, resulting in a tensile stress on the articular surface of the femoral condyle. (See 3.2.2.)1.3 Different designs can be characterized as, but not limited to, posterior cruciate ligament retaining (CR), posterior stabilizing (PS), and revision.1.4 This standard does not address evaluation of femoral components under opening-style loading conditions which have also generated clinical failures. Under opening-style loading conditions, forces are applied to the inner contour of the femoral component in a way that the forces act to increase the intercondylar depth, or open the femoral component.1.5 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.