1、Designation: F2777 10Standard Test Method forEvaluating Knee Bearing (Tibial Insert) Endurance andDeformation Under High Flexion1This standard is issued under the fixed designation F2777; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This standard specifies a test method for determining theendurance properties and deformation, under
3、specified labora-tory conditions, of ultra high molecular weight polyethylene(UHMWPE) tibial bearing components used in bicompartmen-tal or tricompartmental knee prosthesis designs.1.2 This test method is intended to simulate near posterioredge loading similar to the type of loading that would occur
4、during high flexion motions such as squatting or kneeling.1.3 Although the methodology described attempts to iden-tify physiological orientations and loading conditions, theinterpretation of results is limited to an in vitro comparisonbetween knee prosthesis designs and their ability to resistdeform
5、ation and fracture under stated test conditions.1.4 This test method applies to bearing components manu-factured from UHMWPE.1.5 This test method could be adapted to address unicom-partmental total knee replacement (TKR) systems, providedthat the designs of the unicompartmental systems have suffi-ci
6、ent constraint to allow use of this test method. This testmethod does not include instructions for testing two unicom-partmental knees as a bicompartmental system.1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.7 This stan
7、dard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 A
8、STM Standards:2F1223 Test Method for Determination of Total Knee Re-placement ConstraintF2003 Practice for Accelerated Aging of Ultra-High Mo-lecular Weight Polyethylene after Gamma Irradiation inAirF2083 Specification for Total Knee Prosthesis2.2 Other Standards:3ISO 4965 Axial Load Testing Machine
9、sDynamic ForceCalibrationStrain Gauge TechniqueISO 5833 Implants for SurgeryAcrylic Resin Cements3. Terminology3.1 Definitions:3.1.1 anatomic (mechanical) axis of the femurthe linebetween the center of the femoral head and the center of thefemoral knee.3.1.2 bearing centerlinethe line running antero
10、posteriorthat is the mirror line of the femoral articulating surface. Forasymmetric bearing tibial tray designs, the appropriate tibialtray centerline shall be determined and reported along with therationale for the location.3.1.3 bearing retention mechanismmechanical means forpreventing tibial tray
11、/bearing disassociation.3.1.4 femoral component centerlinea line running antero-posterior between the femoral condyles and parallel to thefemoral condyles. The line should be equidistant between thecondyles. For asymmetric or non parallel condyles designs, theappropriate centerline shall be determin
12、ed, and the rationale forthat location reported.3.1.5 fixed bearing systema knee prosthesis system com-prised of a femoral component and a tibial component, wherethe tibial articulating surface is not intended to move relative tothe tibial tray.3.1.6 mobile bearingthe component between fixed femo-ra
13、l and tibial knee components with an articulating surface onboth the inferior and superior sides.3.1.7 mobile bearing knee systema knee prosthesis sys-tem comprised of a femoral component, a tibial component,and a mobile bearing component that can rotate and/or translaterelative to the tibial compon
14、ent.1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devices and is the direct responsibility of SubcommitteeF04.22 on Arthroplasty.Current edition approved Sept. 15, 2010. Published October 2010. DOI:10.1520/F2777-10.2For referenced ASTM standar
15、ds, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, N
16、ew York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.8 posterior slopethe angle that the perpendicular axisof the tibial tray makes when it is tilted posteriorly away fromthe tibial axis (see Fig.
17、 1).3.1.9 R valuethe ratio of the minimum force to themaximum force (that is, R = minimum force/maximum force).3.1.10 tibial axisnominal longitudinal axis of the tibia,which corresponds with the central axis of the medullary cavityof the proximal tibia.3.1.11 tibial tray/bearing disassociationunreco
18、verablephysical separation of the tibial bearing and tibial tray compo-nents as a result of bearing distraction or tilting.3.1.12 tibial tray centerlinea line running anteroposteriorthat is the mirror line of the tibial articulating surface. Forasymmetric bearing tibial tray designs, the appropriate
19、 tibialtray centerline shall be determined and reported along with therationale for the location.4. Significance and Use4.1 This test method can be used to describe the effects ofmaterials, manufacturing and design variables on the fatigue/cyclic creep performance of UHMWPE bearing componentssubject
20、 to substantial rotation in the transverse plan (relative tothe tibial tray) for a relatively large number of cycles.4.2 The loading and kinematics of bearing componentdesigns in vivo will, in general, differ from the loading andkinematics defined in this test method. The results obtainedhere cannot
21、 be used to directly predict in vivo performance.However, this test method is designed to enable comparisonsbetween the fatigue performance of different bearing compo-nent designs when tested under similar conditions.4.3 The test described is applicable to any bicompartmentalknee design including mo
22、bile bearing knees that have mecha-nisms in the tibial articulating component to constrain theposterior movement of the femoral component and a built inretention mechanism to keep the articulating component on thetibial plate.5. Apparatus and Materials5.1 Testing machine, with the following characte
23、ristics:5.1.1 A sinusoidal, dynamic-forcing waveform.5.1.2 An error in applied force not greater than 62 % at themaximum force magnitude (in accordance with ISO 4965).5.1.3 The axial force peak representative of what couldoccur during daily activities of high flexion is a force of about2275 N. Durin
24、g the tests, the values of the maximum andminimum forces shall be maintained to an accuracy of 62%ofthe maximum force. The test shall be stopped if this accuracyis not maintained.5.1.4 The forcing accuracy must be maintained as bearingcomponent deformation occurs.5.1.5 Instrumentation to record the
25、number of cycles.5.2 Fixturing:5.2.1 Means of mounting and enclosing the test specimensusing a corrosion-resistant material that is capable of holdingthe femoral component and tibial tray.5.2.2 The fixtures shall maintain the tibial and femoralcomponents in their required orientations for the durati
26、on ofthe test.5.2.3 If necessary, bone cement (see ISO 5833) or a high-strength epoxy may be used to lock the femoral and tibialcomponents in their fixtures.5.2.4 The test apparatus or fixture should allow the force tobe applied through the center of the femoral component andensure equal force trans
27、mission through the medial and lateralcondyles.5.3 Fluid Medium:5.3.1 The test assembly shall be immersed in deionizedwater at 37 6 2C.5.3.2 Water should be added as necessary to keep the testcomponents at the test temperature for the duration of the test.FIG. 1 Incline the Ttibial Tray Relative to
28、the Tibial Axis at the Recommended Angle (Posterior Slope)F2777 1026. Specimen Selection6.1 The metallic components shall follow the completemanufacturing process (machining, surface treatment, lasermarking, passivation, cleaning, and so forth) until the steril-ization stage. Because sterilization h
29、as no known effect on themechanical properties for metallic components, it is not nec-essary for these to be sterilized. Unlike the metal components,the UHMWPE components shall be sterilized in a mannerconsistent with the clinical use for such devices, as this mayaffect the mechanical properties of
30、the material.6.2 The UHMWPE component(s) shall be artificially agedaccording to Practice F2003, except when the mechanicalproperties of the UHMWPE have been proven not to bedetrimentally affected by aging.6.3 Most of the knee systems allow the tibial tray to beupsized, size for size or downsized rel
31、ative to the bearingcomponent size. Consistent with the principle of this testmethod, the smallest tibial tray compatible with a givenbearing component size (according to the manufacturer) shallbe used.6.4 There may be some small variation in the amount ofcold flow of the bearing component depending
32、 on the tibialbearing thickness. However, the possible effect of the cold flowis the worst on the thinnest bearing components. Consequently,the thinnest bearing component in the knee system scope shallbe used in this test.7. Procedure7.1 On one representative sample, make the initial measure-ments o
33、n the bearing surface to characterize the subsequentamount of bearing deformation after completion of the test.Use of a Coordinate Measuring Machine (CMM) is therecommended method of making the measurements. Themeasurements should be in the form of a grid of points,referenced to a fixed plane on the
34、 UHMWPE bearing, 1.5 mmapart over the entire superior surface of the UHMWPE bearing.The measurements should be made with the bearing at 206 2C.7.2 On one representative sample, perform the “A-P DrawTest” (Section 9.2) and the “Rotary Laxity Test” (Section 9.4)from Test Method F1223 at the same flexi
35、on angle used in 7.6of this test method.7.3 The UHMWPE bearing shall be conditioned in a deion-ized water environment at 37 6 2C prior to initiation of thetest for a long enough time to bring the bearing into equilib-rium with the fluid temperature.7.4 Mount the tibial tray in the test machine. The
36、mainproximal planar surface shall be inclined at the posterior sloperecommended by the manufacturer (see Fig. 1). If more thanone slope is recommended, the largest slope should be used.Mount the bearing component on the tibial tray using themethod recommended by the manufacturer.NOTE 1The tibial slo
37、pe will generate a shear force and a resultingbending moment on the test frame actuator. This may cause a significanterror of the load cell, depending on the sensitivity of the load cell to offaxis loading. This should be addressed in the test setup.7.5 Measure vertical distraction (when appropriate
38、 for thedesign) and bearing tilt (Fig. 2).7.5.1 To measure the vertical distraction, use appropriately-sized feeler gauges, one set under each condyle to lift thebearing away from the tibial plate keeping the posterior surfaceof the bearing parallel to the superior surface of the tibial plate,until
39、the gauges will not fit easily in the gap. The thickness ofthe feeler gauges is the vertical distraction value.7.5.2 To measure the posterior bearing tilt displacement,push the bearing posteriorly and raise the posterior edge of thebearing by hand. Select a location on the posterior edge of thebeari
40、ng and measure the perpendicular distance from thatlocation to the tibial plate. Change in these displacements aftertesting may be useful as an indicator of damage.7.6 Mount the femoral component in the test machine withan alignment such that the component is flexed in the sagittalplane at the maxim
41、um flexion angle (including the posteriorslope angle) the manufacturer recommends (see Fig. 3) accord-ing to the method in Section 6.1.3 of Specification F2083.7.7 The femoral component should be placed so that itcontacts the bearing component close to the posterior edge ofthe bearing. The specific
42、contact points between componentsshould be recorded and justified. At minimum, it should bedemonstrated that the anterior-posterior placement of thecomponents would permit flexion and rotation of the femur tothe prescribed angles without impingement between the femurand tibia.NOTE 2If the mobile bea
43、ring knee design allows anterior-posteriortranslation of the mobile bearing, translate the bearing componentposteriorly relative to the tibial tray (according to the maximum transla-tion allowed by the knee system) to simulate a worst-case condition.7.8 Initially align the all components in neutral
44、rotation toset the maximum flexion angle. In this position, the femoralcomponent, the bearing component and the tibial tray anterior-posterior centerlines are coplanar (see Fig. 4).7.9 Rotational Alignment:7.9.1 For mobile bearing knee system designs simulate 20of internal rotation for the tibial tr
45、ay with respect to the femoraland bearing components (see Fig. 5).NOTE 3The femoral component and the anteroposterior centerlines ofthe bearing component are still collinear.7.9.2 For fixed designs, the components should simulate 20of internal rotation for the tibia tray with respect to the femoralF
46、IG. 2 Vertical Distraction and Posterior Bearing Tilt DisplacementF2777 103component. If a smaller angle is used, it shall be justified (seeFig. 6). On a fixed bearing system, only one femoral condyleshall be at the maximum posterior contact point after theinternal rotation is simulated. The other c
47、ondyle shall be closerto the center of the bearing. It may be necessary to change thevarus-valgus orientation of the tibial component to bring bothfemoral condyles into contact with the bearing before applyingforce. It may also be necessary to achieve the 20 rotation byrotating the femoral component
48、, as long as the appropriateflexion and load line are correct.7.9.3 The line of force application shall be set to passthrough the femoral component centerline intersecting at orposterior to the contact points.7.10 Introduce the water to completely immerse the testspecimen contact surfaces.7.11 Start
49、 the test machine and apply a cyclical force with apeak of 2275 N to the bearing component with the femoralcomponent at the specified force. For these tests, the ratio ofthe minimum force magnitude to the maximum force magni-tude should be 0.1.7.12 Operate the testing machine at a fixed frequencybetween 0.5 to 2.0 Hz.7.13 Measure the bearing component deflection through thetesting machine. If bearing tilt occurs under load, it shall berecorded and if possible measured for the duration of the test.7.14 Continue the test until one of the following eventsoccur:
