1、Designation: F 2723 08Standard Test Method forEvaluating Mobile Bearing Knee Tibial Baseplate/BearingResistance to Dynamic Disassociation1This standard is issued under the fixed designation F 2723; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e of revision, 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 test method describes a laboratory method forevaluating the potential for mobile beari
3、ng knee tibialbaseplate/bearing disassociation under repeated forces.1.2 The test described is applicable to any bicompartmentalmobile bearing knee with a bearing retention mechanism. Withmodification, the test can be applied to a unicompartmentalmobile bearing knee with a bearing retention mechanis
4、m.1.3 Although the methodology described does not replicateall physiological force conditions, it is a means of in vitrocomparison of mobile bearing knee designs and the strength ofthe bearing retention mechanism between the tibial baseplateand bearing components under the stated test conditions.1.4
5、 The values stated in SI units are regarded as standard.1.5 This standard 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-bilit
6、y of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2F 1223 Test Method for Determination of Total Knee Re-placement Constraint3. Terminology3.1 Definitions:3.1.1 bearing axisthe line connecting the lowest points onboth the lateral and medial condyles of the superior s
7、urface ofthe mobile bearing.3.1.2 bearing retention mechanismmechanical meanspreventing tibial baseplate/bearing disassociation.3.1.3 inferior articulating interfacesany interface inwhich relative motion occurs between the underside of themobile bearing component and the tibial tray.3.1.4 limiting p
8、ositionthe position of the femoral compo-nent relative to the bearing at which the shear force is at amaximum with anterior-posterior (AP) movement of the femo-ral component on the bearing.3.1.5 mobile bearingthe component between fixed femo-ral and tibial knee components with an articulating surfac
9、e onboth the inferior and superior sides.3.1.6 mobile bearing knee systema knee prosthesis sys-tem, comprised of a tibial component, a mobile bearingcomponent that can rotate or rotate and translate relative to thetibial component, and a femoral component.3.1.7 superior articulating interfacesany in
10、terface inwhich relative motion occurs between the topside of the mobilebearing component and the femoral bearing component.3.1.8 tibial baseplate/bearing disassociationunrecoverable physical separation of the bearing and tibialbaseplate components as a result of bearing distraction ortilting.3.1.9
11、2-axis orthogonal load framea test machine capableof applying forces and displacements that act at 90 to eachother.4. Significance and Use4.1 This test method includes the use of static and fatigueshear and bending force conditions to evaluate the bearingretention mechanism of a mobile bearing knee
12、design and itsability to prevent disassociation.4.2 In general, disassociation does not occur during activi-ties where the contact locations are within the boundaries of thebearing surfaces. Disassociation is most likely to occur withforces at the edges of the bearing component or with large APshear
13、 forces on a posterior stabilized knee tibial componentpost. Extreme bearing rotation, bone/bearing impingement,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.Curren
14、t edition approved June 1, 2008. Published July 2008.2For referenced ASTM standards, 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.1Copyrig
15、ht ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.severe varus or valgus moments, high flexion or any combi-nation of the above can increase the likelihood of disassocia-tion.4.3 The test method described is applicable to any bicom-partmental
16、mobile bearing knee with a bearing retentionmechanism. With modification, the test can be applied to aunicompartmental mobile bearing knee with a bearing reten-tion mechanism.5. Apparatus and Materials5.1 A2-axis orthogonal load frame with feedback control onboth axes be required for dislocation tes
17、ting. The machine mustbe able to record force and displacement in both axes.5.1.1 Component SizeTest specimens should be chosen tomaximize the force on the bearing retention mechanism.Considerations should include bearing thickness (a thickerbearing would tend to increase the forces on the lockingme
18、chanism, but could also increase the material support for thelocking mechanism), bearing profile/size and tibial baseplateprofile/size (a large bearing on a small tibial baseplate wouldtend to increase the overhang with rotation).5.1.2 Component QuantityThe minimum number of testsamples shall be fiv
19、e.5.2 Component ConfigurationsThe mobile bearing kneecomponents should be assembled, as they would be for in-vivouse.5.2.1 The femoral component flexion angle should be cho-sen to maximize the forces on the bearing retention mecha-nism. An engineering analysis may be necessary to determinethe approp
20、riate femoral flexion angle that creates the largestshear and/or bending forces on the retention mechanisms. Forexample, for a gait congruent design, a 0 flexion angle mightdistribute forces on both the anterior and the posterior sides ofthe locking mechanism, minimizing any bending forces. Aflexion
21、 angle of greater than 90 may maximize the posteriorposition of the femoral component and consequently increasebending forces on the retention mechanism.5.2.2 The tibial baseplate should be positioned with therecommended posterior slope. For knee systems where morethan one posterior slope is recomme
22、nded, the largest slopeshould be used.5.2.3 Component FixturesThe femoral component isfixed at the desired flexion angle. The tibial baseplate should befixtured with the appropriate posterior slope. The tibial fixturesmust allow the tibial baseplate to be fixed in relative rotation tothe bearing and
23、 the femoral components. The test specimencoordinate system is shown in Fig. 1. Fixtures should notinhibit free motion of the bearing, even with substantialdeformation if it should occur.5.2.4 Applied ForceThe 3500 N vertical axial forceshould be maintained within 63 % for the duration of the test.T
24、he test apparatus or fixtures should allow the force to beapplied through the center of the femoral component (Vc, Fig.1) to be distributed to the contact points with the tibialcomponent. The peak cyclic horizontal force applied to thetibial baseplate should be maintained within 63 % for theduration
25、 of the test.5.2.5 Displacement MeasurementDisplacement sensingdevices should be capable of measuring the relative motionbetween the femoral and tibial baseplate in the anterior-posterior direction.5.2.6 Oscillating FrequencyThe cyclic horizontal forceshould be applied at a frequency of 0.5 to 3.0 c
26、ycles per second(0.5 to 3.0 Hz).5.2.7 Cycle CounterThe test apparatus should beequipped with a cycle counter to record the total number ofhorizontal test cycles.6. Test Specimens6.1 The total knee replacement (TKR) should be the manu-facturers designated “standard” or “medium” size unless thebearing
27、 retention mechanism varies with the size of the knee.If the retention mechanism does vary, an engineering analysisshould be conducted to justify a “worst case.”6.2 The implant shall be in its original packaging assupplied to the user by the manufacturer.6.3 If the implant is not available in its pa
28、ckage state, thecondition of the device shall meet all geometry and materialspecifications, but may contain slight surface irregularities(that is, “cosmetic rejects”) not considered influential in thoseregions of the device deemed critical to the specific test.7. Conditioning7.1 Expose the test spec
29、imens to a clean atmosphere at atemperature of 37 6 2C for 24 h prior to testing.7.2 The test shall be run in a bath at 37 6 2C that coversthe tibial bearing surface. The bath can be either bovine serum,mineral oil, olive oil, or deionized water. Before testing, theimplant must be moved cyclically t
30、hree times in the desireddirection before data are acquired. These three repetitions canbe performed by hand. This procedure is intended to distributelubricant between the bearing surface and the tibial component.FIG. 1 Coordinate System and Force LocationsF2723082If the bearing is installed on the
31、tibial component in thepresence of lubricant it can be omitted.8. Procedure8.1 Assemble the bearing and tibial baseplate.8.2 Measure vertical distraction (when appropriate for thedesign) and bearing tilt (Fig. 2). These measurements are madeby manipulating the bearing on the tibial plate by hand wit
32、hminimal force. Change in these displacements after testing maybe useful as an indicator of damage.8.3 Place test specimens in test apparatus using the appro-priate fixtures.8.3.1 The femoral component should be fixed at the desiredflexion angle relative to the tibial baseplate.8.3.2 The tibial base
33、plate and bearing should be approxi-mately centered under the femoral component. The tibialbaseplate should be axially aligned with the femoral compo-nent, that is, 0 of relative rotation. The bearing can be allowedto rotate slightly less than 5 when the force is applied toaccommodate the possible v
34、ariation in the flexion radii of thecondyles of the femoral component.8.3.3 The femoral component should apply the force alongthe bearing axis of the bearing.8.4 Apply the 3500 N vertical axial force, that is, jointreaction force.8.5 Limit Measurement Setup:8.5.1 Apply a posterior-to-anterior horizo
35、ntal force to thetibial base plate until the horizontal force reaches 450 N3or thefemoral component reaches a point where the horizontal forcedrops because the femur has crossed over the posterior edge ofthe tibial component. The plot of AP force versus AP displace-ment is continuously recorded.8.5.
36、1.1 If the force reaches 450 N, the posterior-to-anteriorlimit force is 450 N.8.5.1.2 If the force drops off before 450 N, the posterior-to-anterior limit force is 90 % of the peak force.8.5.2 Apply an anterior-to-posterior horizontal force to thetibial base plate until the horizontal force reaches
37、450 N or thefemoral reaches a point where the horizontal force dropsbecause the femur has crossed over the anterior edge of thetibial component. The plot of AP force versus AP displacementis continuously recorded.8.5.2.1 If the force reaches 450 N, the anterior-to-posteriorlimit force is 450 N.8.5.2
38、.2 If the force drops off before 450 N, the anterior-to-posterior limit force is 90 % of the peak force.8.6 Using the information from 8.5, apply a cyclic APhorizontal force to the tibial baseplate. The peak force in theanterior to posterior direction will be the limit force for thatdirection determ
39、ined in 8.5.2. The peak force in the posterior toanterior direction will be the limit force for that directiondetermined in 8.5.1.8.7 Run for 110 000 cycles or until failure of the bearingretention mechanism.8.8 Record the anterior/posterior displacement for cycles110 000 and 220 000.8.9 Measure ver
40、tical distraction and bearing tilt (Fig. 2)asin 8.2.8.10 Repeat the test with the tibial baseplate fixed in relativerotation to the femoral component and the bearing. Therotation should result in bearing overhang. The amount ofrotation should be justifiable based on clinical conditions (20of rotatio
41、n suggested, but may vary with design). If the mobilebearing design is not symmetrical, the direction (internal orexternal) of rotation should be chosen in order to maximize thebearing overhang. Run to 110 000 cycles or until failure of thebearing retention mechanism. The cyclic AP horizontal forces
42、hould be applied in line with the femoral component.8.11 Record the anterior/posterior displacement for the lastcycle.8.12 Measure vertical distraction and bearing tilt (Fig. 2).8.13 Replace the test specimens on test apparatus with norelative rotation between bearing and tibial baseplate.8.14 Apply
43、 a steadily increasing anterior-to-posterior forceon the tibial baseplate until failure occurs.8.14.1 Record failure mode, for example, upper bearingdisassociation (subluxation/dislocation), lower bearing disas-sociation, bearing retention mechanism failure, post failure ina posterior stabilized kne
44、e design.8.14.2 Record failure force.9. Report9.1 Materials:9.1.1 Record size information and justify the choice of size.9.1.2 Provide material traceability information for eachcomponent. Examples of such information include part num-ber, batch/lot number, material grade, and processing variables.9.
45、1.3 The method of sterilization should be reported. Forirradiation-sterilized specimens, total dose and dose rate shouldbe reported.9.2 Test Apparatus and Methodology:9.2.1 Describe the mechanisms used to generate the forces,the systems used to measure the forces and displacements, thefixtures, and
46、the lubricant.9.2.2 Report and justify the femoral flexion angle chosen forthe test.FIG. 2 Vertical Distraction and Bearing TiltF27230839.2.3 Report and justify the posterior slope of the tibial platethat was used in the test.9.2.4 Report the number of cycles per second.9.2.5 Report the horizontal r
47、ate of force application.9.2.6 Report the amount of rotation of the tibial baseplatethat was applied per 8.10 with justification for the amount.9.3 Outcome:9.3.1 Report the anterior and posterior tibial baseplatedisplacement at the beginning of the test, after 110 000 cyclesand after 220 000 cycles.
48、9.3.2 Report the vertical distraction and the bearing tiltvalues at the beginning of the test, after 110 000 cycles, andafter 220 000 cycles.9.3.3 Report any bearing disassociation, imminent disasso-ciation, or serious damage to the bearing retention mechanismafter 220 000 cycles.9.3.4 Describe the
49、ultimate failure mode and peak force asa result of the steadily increasing anterior-to-posterior tibialforce as applied per 8.14.APPENDIX(Nonmandatory Information)X1. RATIONALEX1.1 Failure of currently available mobile bearing kneedesigns by bearing distraction or tilting is not common, asevidenced by the lack of bearing retention mechanism failuresreported in the English-language literature.X1.2 The cyclic portion of this test is representative of lowcycle activities of daily living (gait with tibiofemoral contact atthe extremes or high flexion). The describ
