1、Designation: F 2724 08Standard Test Method forEvaluating Mobile Bearing Knee Dislocation1This standard is issued under the fixed designation F 2724; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numbe
2、r 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 is designed to provide a standardizedmethod to determine the dislocation resistance of mobile-bearing knee designs with reg
3、ard to femoral componentdisassociation and spin-out/spit-out of the mobile bearinginsert.1.2 Although the methodology described does not replicateall physiological loading conditions, it is a means of in-vitrocomparison of mobile bearing knee designs and their ability toresist dislocation of the mob
4、ile bearing from the femoral ortibial components under stated test conditions.1.3 The test method applies only to mobile bearing totalknee designs.1.4 The values stated in SI units are regarded as standard.The values given in parentheses are mathematical conversionsto inch-pound units that are provi
5、ded for information only andare not considered 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 axis, nthe line connecting the lowest pointson both the lateral and medial condyles of the superio
7、r surfaceof the mobile bearing.3.1.2 centerline axis, na line through the neutral pointperpendicular to the bearing axis and in a plane parallel to theplane of the flat portion of the inferior articulating surface ofthe mobile bearing at 0 posterior tibial slope.3.1.3 mobile bearing (insert), nthe c
8、omponent betweenfixed femoral and tibial knee components with an articulatingsurface on both the inferior and superior sides.3.1.4 neutral point, nmidpoint of the bearing axis.3.1.5 spin-out, nexcessive rotation of the bearing compo-nent in a rotating platform knee or multi-directional platformknee
9、such that there is dislocation between the femoral or tibialcomponents and the mobile bearing.3.1.6 spit-out, nescape of the bearing component frombeneath the femoral component either anteriorly or posteriorly.3.1.7 2-axis orthogonal load frame, na test machinecapable of applying forces and displace
10、ments that act at 90 toeach other.4. Significance and Use4.1 This test method is designed to provide a standardizedmethod to determine the constraint of mobile-bearing kneedesigns with regards to spin-out and spit-out of the mobilebearing.4.2 Similar to constraint testing of total knees (see TestMet
11、hod F 1223), it is important to note that the test methoddoes not simulate the soft tissues and laxity of the knee joint,which may be key factors related to the occurrence of spin-outor spit-out.3For instance, a patient with good soft tissuerestraints will perhaps require a lower spin-out/spit-out r
12、esis-tance whereas a patient with major bone loss or destroyedligamentous structures will likely require an implant with ahigher spin-out/spit-out resistance. Therefore, the results fromthe test should be taken into account along with the conditionof the patients soft tissues to determine the relati
13、ve safety forthe device.5. Apparatus and Materials5.1 A engineering analysis should be performed on all sizesof a knee design to justify a “worst case” size for this test. Atleast five mobile bearing inserts of that size should be tested.The tibial tray and knee femoral component may be reused formu
14、ltiple trials as long as they are not damaged during testing.5.2 The mobile bearing surfaces shall be lightly coated withbovine serum, olive oil, mineral oil, or deionized water toreduce friction effects during testing.1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland S
15、urgical Materials and Devices and is the direct responsibility of SubcommitteeF04.22 on Arthroplasty.Current 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
16、 ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Weale, A. E., et al, “In Vitro Evaluation of the Resistance to Dislocation of aMeniscal-Bearing Total Knee Prosthesis Between 30 and 90 of Knee Flexion,” J.Arthroplasty, 17( 4), 2002, pp. 475483.1Copy
17、right ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.3 A 2-axis orthogonal load frame with feedback controlshall be used for dislocation testing. The machine must be ableto record force and displacement in both axes.5.4 Fixtures shall be req
18、uired to allow for an 80 % medialand 20 % lateral load distribution to be applied through thecondyles of the femoral component.45.5 During testing, the tibial tray posterior slope and femo-ral component degree of flexion should be set according to therecommended surgical alignment.6. Specimen Prepar
19、ation6.1 All components should be inspected prior to testing toensure that they meet the geometrical and material specifica-tions. The tibial inserts should undergo sterilization as wouldnormally be employed with actual implants.6.2 The test components should be exposed to a cleanatmosphere at a tem
20、perature of 25 6 5C for 24 h prior totesting.7. Procedure7.1 Dislocation testing should be performed at 0, 60, and90 of flexion, as well as the maximum flexion angle that theimplant is intended to achieve. The test procedure shall addressspin-out and spit-out simultaneously if allowed by the design.
21、7.2 Either the tibial tray or the femoral component shall befree to translate under actuator control in the anterior andposterior (A/P) directions. A compressive joint reaction forceshall be applied to the mobile bearing knee through either thetibial tray or the femoral component along the superior/
22、inferior(S/I) direction. The femoral component should be oriented inthe desired flexion angles for the testing. The femoral compo-nent shall be constrained in all other translations/rotations.7.3 The tibial tray should be mounted into fixtures thatallow varus/valgus tilt. The pivot axis for the tilt
23、 should beselected based on calculations to apply 80 % of the force on themedial condyle and 20 % of the force on the lateral condyle.This can be accomplished by offsetting the pivot axis from thecenterline axis in the medial direction by 30 % of total bearingspacing. The posterior slope of the tibi
24、al plate should be theslope recommended in the surgical procedure for the device.7.4 The tibial tray will be constrained in all othertranslations/rotations not mentioned in 7.2 or 7.3.7.5 The components should be adjusted to the zero rotationposition prior to testing. A joint reaction force of 710 N
25、 (160lbf) should be applied along the S/I axis and held constant. Thefemoral component should be positioned on the articulatingsurface at the same starting location, the approximate low pointper design of both the lateral and medial condylar articulatingsurfaces at zero rotation, under a 50 N load p
26、rior to testing. Thefemoral component should be displaced anteriorly until contactis lost with either of the insert condyles.7.6 The components will be realigned to the original posi-tion. The joint load of 710 N (160 lbf) will be reapplied alongthe S/I axis and the femoral component should then bed
27、isplaced posteriorly until contact is lost with either of theinsert condyles.8. Reporting Results8.1 Report the following information:8.1.1 Justification for the choice of the knee size tested.8.1.2 The total femoral displacement relative to the tibialtray and the S/I axis should be reported for eac
28、h individualtrial.8.1.3 The maximum loads should be reported for eachindividual trial.8.1.4 The mode of failure that occurs first, spin-out orspit-out, should be reported for each individual trial.APPENDIX(Nonmandatory Information)X1. RATIONALEX1.1 Spin-out and spit-out of mobile bearing inserts has
29、been found clinically to be a mode of failure, with a rate of lessthan 9.3 % reported in the literature.5X1.2 The applied load of 710 N (160 lbf) was selectedbased on the applied load in Test Method F 1223. The load wasselected to provide a relative comparison between devices andis not intended to b
30、e related to any physiological load.X1.3 The 80 % medial/20 % lateral load distribution speci-fied in this test method was selected to represent an extremecase where the majority of the load is applied to a singlecondyle, increasing the probability that spin-out/spit-out mayoccur. Based on one study
31、 reported in the literature,4the mostcommon loading distribution was 60 % medial/40 % lateral,with the majority of patients below the 80 % medial load levelthat was selected as a worst case for this test method.4Hurwitz, D. E., et al, “Dynamic Knee Loads During Gait Predict ProximalTibial Bone Distr
32、ibution,” J. Biomechanics, 31, 1998, pp. 423430.5Bert, J. M., “Dislocation/Subluxation of Meniscal Bearing Elements After NewJersey Low-Contact Stress Total Knee Arthroplasty,” Clin. Orthop., 254, May 1990,pp. 211215.F2724082ASTM International takes no position respecting the validity of any patent
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36、 ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).F2724083
