1、Designation: F2723 13Standard Test Method forEvaluating Mobile Bearing Knee Tibial Baseplate/BearingResistance to Dynamic Disassociation1This standard is issued under the fixed designation F2723; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、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 bearing
3、 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 mechanism.
4、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 T
5、he values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.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-pri
6、ate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Terminology2.1 Definitions:2.1.1 bearing axisthe line connecting the lowest points onboth the lateral and medial condyles of the superior surface ofthe mobile bearing.2.1.2 bearing retention me
7、chanismmechanical means pre-venting tibial baseplate/bearing disassociation.2.1.3 inferior articulating interfacesany interface inwhich relative motion occurs between the underside of themobile bearing component and the tibial tray.2.1.4 limiting positionthe position of the femoral compo-nent relati
8、ve to the bearing at which the shear force is at amaximum with anterior-posterior (AP) movement of the femo-ral component on the bearing.2.1.5 mobile bearingthe component between fixed femo-ral and tibial knee components with an articulating surface onboth the inferior and superior sides.2.1.6 mobil
9、e bearing knee systema knee prosthesissystem, comprised of a tibial component, a mobile bearingcomponent that can rotate or rotate and translate relative to thetibial component, and a femoral component.2.1.7 superior articulating interfacesany interface inwhich relative motion occurs between the top
10、side of the mobilebearing component and the femoral bearing component.2.1.8 tibial baseplate/bearing disassociation unrecover-able physical separation of the bearing and tibial baseplatecomponents as a result of bearing distraction or tilting.2.1.9 2-axis orthogonal load framea test machine capableo
11、f applying forces and displacements that act at 90 to eachother.3. Significance and Use3.1 This test method includes the use of static and fatigueshear and bending force conditions to evaluate the bearingretention mechanism of a mobile bearing knee design and itsability to prevent disassociation.3.2
12、 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 forces on a posterior stabilized knee tibial compo
13、nentpost. Extreme bearing rotation, bone/bearing impingement,severe varus or valgus moments, high flexion or any combi-nation of the above can increase the likelihood of disassocia-tion.3.3 The test method described is applicable to any bicom-partmental mobile bearing knee with a bearing retentionme
14、chanism. With modification, the test can be applied to aunicompartmental mobile bearing knee with a bearing reten-tion mechanism.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 Ar
15、throplasty.Current edition approved Feb. 1, 2013. Published February 2013. Originallyapproved in 2008. Last previous version approved in 2008 as F2723 08. DOI:10.1520/F2723-13.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Apparat
16、us and Materials4.1 A2-axis orthogonal load frame with feedback control onboth axes be required for dislocation testing. The machine mustbe able to record force and displacement in both axes.4.1.1 Component SizeTest specimens should be chosen tomaximize the force on the bearing retention mechanism.C
17、onsiderations should include bearing thickness (a thickerbearing would tend to increase the forces on the lockingmechanism, 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 would
18、tend to increase the overhang with rotation).4.1.2 Component QuantityThe minimum number of testsamples shall be five.4.2 Component ConfigurationsThe mobile bearing kneecomponents should be assembled, as they would be for in-vivouse.4.2.1 The femoral component flexion angle should be cho-sen to maxim
19、ize the forces on the bearing retention mecha-nism. An engineering analysis may be necessary to determinethe appropriate 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 f
20、orces on both the anterior and the posterior sides ofthe locking mechanism, minimizing any bending forces. Aflexion angle of greater than 90 may maximize the posteriorposition of the femoral component and consequently increasebending forces on the retention mechanism.4.2.2 The tibial baseplate shoul
21、d be positioned with therecommended posterior slope. For knee systems where morethan one posterior slope is recommended, the largest slopeshould be used.4.2.3 Component FixturesThe femoral component is fixedat the desired flexion angle. The tibial baseplate should befixtured with the appropriate pos
22、terior slope. The tibial fixturesmust allow the tibial baseplate to be fixed in relative rotation tothe bearing and 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 occu
23、r.4.2.4 Applied ForceThe vertical axial force should bemaintained within 63 % for the duration of the test. The testapparatus or fixtures should allow the force to be appliedthrough the center of the femoral component (Vc, Fig. 1)tobedistributed to the contact points with the tibial component. Thepe
24、ak cyclic horizontal force applied to the tibial baseplateshould be maintained within 63 % for the duration of the test.4.2.5 Displacement MeasurementDisplacement sensingdevices should be capable of measuring the relative motionbetween the femoral and tibial baseplate in the anterior-posterior direc
25、tion.4.2.6 Oscillating FrequencyThe cyclic horizontal forceshould be applied at a frequency of 0.5 to 3.0 cycles per second(0.5 to 3.0 Hz).4.2.7 Cycle CounterThe test apparatus should beequipped with a cycle counter to record the total number ofhorizontal test cycles.5. Test Specimens5.1 The total k
26、nee replacement (TKR) should be the manu-facturers designated “standard” or “medium” size unless thebearing 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.”5.2 The implant shall be in its
27、original packaging assupplied to the user by the manufacturer.5.3 If the implant is not available in its package state, thecondition of the device shall meet all geometry and materialspecifications, but may contain slight surface irregularities(that is, “cosmetic rejects”) not considered influential
28、 in thoseregions of the device deemed critical to the specific test.6. Conditioning6.1 Expose the test specimens to a clean atmosphere at atemperature of 37 6 2C for 24 h prior to testing.6.2 The test shall be run in a bath at 37 6 2C that coversthe tibial bearing surface. The bath can be either bov
29、ine serum,mineral oil, olive oil, or deionized water. Before testing, theimplant must be moved cyclically three 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 t
30、he tibial component.If the bearing is installed on the tibial component in thepresence of lubricant it can be omitted.7. Procedure7.1 Assemble the bearing and tibial baseplate.7.2 Measure vertical distraction (when appropriate for thedesign) and posterior bearing tilt displacement (Fig. 2). Changein
31、 these displacements after testing may be useful as anindicator of damage.FIG. 1 Coordinate System and Force LocationsF2723 1327.2.1 To measure the vertical distraction, use plastic blade-type feeler gauges of an appropriate range to measure theamount of distraction. The gauge blades should be long
32、enoughto completely fit under the full length of the bearing. One setshall be placed under each condyle to lift the bearing awayfrom the tibial plate keeping the posterior surface of thebearing parallel to the superior surface of the tibial plate, untilthe gauges will not fit in the gap without forc
33、e. The thicknessof the feeler gauges is the vertical distraction value.7.2.2 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 inferior-posterioredge of the bearing and measure the perpendicula
34、r distancefrom that location to the tibial plate. The value of thatmeasurement is the posterior bearing tilt displacement.7.3 Place test specimens in test apparatus using the appro-priate fixtures.7.3.1 The femoral component should be fixed at the desiredflexion angle relative to the tibial baseplat
35、e.7.3.2 The tibial baseplate and bearing should be approxi-mately centered under the femoral component. The tibialbaseplate should be axially aligned with the femoralcomponent, that is, 0 of relative rotation. The bearing can beallowed to rotate slightly less than 5 when the force is appliedto accom
36、modate the possible variation in the flexion radii ofthe condyles of the femoral component.7.3.3 The femoral component should apply the force alongthe bearing axis of the bearing.7.4 Apply a compressive force of 2275 N as the verticalaxial force, that is, joint reaction force.7.5 Limit Measurement S
37、etup:7.5.1 Apply a posterior-to-anterior horizontal 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
38、 AP displace-ment is continuously recorded.7.5.1.1 If the force reaches 450 N, the posterior-to-anteriorlimit force is 450 N.7.5.1.2 If the force drops off before 450 N, the posterior-to-anterior limit force is 90 % of the peak force.7.5.2 Apply an anterior-to-posterior horizontal force to thetibial
39、 base plate until the horizontal force reaches 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.7.5.2.1 If the force reaches 450 N, the
40、anterior-to-posteriorlimit force is 450 N.7.5.2.2 If the force drops off before 450 N, the anterior-to-posterior limit force is 90 % of the peak force.7.6 Using the information from 7.5, apply a cyclic APhorizontal force to the tibial baseplate. The peak force in theanterior to posterior direction w
41、ill be the limit force for thatdirection determined in 7.5.2. The peak force in the posterior toanterior direction will be the limit force for that directiondetermined in 7.5.1.7.7 Run for 110 000 cycles or until failure of the bearingretention mechanism.7.8 Record the anterior/posterior displacemen
42、t for cycles110 000 and 220 000.7.9 Measure vertical distraction and bearing tilt (Fig. 2)asin 7.2.7.10 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 justifi
43、able based on clinical conditions (20of rotation 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 reten
44、tion mechanism. The cyclic AP horizontal forceshould be applied in line with the femoral component.7.11 Record the anterior/posterior displacement for the lastcycle.7.12 Measure vertical distraction and bearing tilt (Fig. 2).7.13 Replace the test specimens on test apparatus with norelative rotation
45、between bearing and tibial baseplate.7.14 Apply a steadily increasing anterior-to-posterior forceon the tibial baseplate until failure occurs.7.14.1 Record failure mode, for example, upper bearingdisassociation (subluxation/dislocation), lower bearingdisassociation, bearing retention mechanism failu
46、re, post fail-ure in a posterior stabilized knee design.7.14.2 Record failure force.FIG. 2 Vertical Distraction and Posterior Bearing Tilt DisplacementF2723 1338. Report8.1 Materials:8.1.1 Record size information and justify the choice of size.8.1.2 Provide material traceability information for each
47、component. Examples of such information include partnumber, batch/lot number, material grade, and processingvariables.8.1.3 The method of sterilization should be reported. Forirradiation-sterilized specimens, total dose and dose rate shouldbe reported.8.2 Test Apparatus and Methodology:8.2.1 Describ
48、e the mechanisms used to generate the forces,the systems used to measure the forces and displacements, thefixtures, and the lubricant.8.2.2 Report and justify the femoral flexion angle chosen forthe test.8.2.3 Report and justify the posterior slope of the tibial platethat was used in the test.8.2.4
49、Report the number of cycles per second.8.2.5 Report the horizontal rate of force application.8.2.6 Report the amount of rotation of the tibial baseplatethat was applied per 7.10 with justification for the amount.8.3 Outcome:8.3.1 Report the anterior and posterior tibial baseplatedisplacement at the beginning of the test, after 110 000 cyclesand after 220 000 cycles.8.3.2 Report the vertical distraction and the posterior bear-ing tilt displacement values at the beginning of the test, after110 000 cycles, and after 220 000 cycles.8.3.3 Report any bearing disa
