ASTM F2724-21

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Designation: F2724 − 08 (Reapproved 2014) F2724 − 21
Standard Test Method for
Evaluating Mobile Bearing Knee Dislocation
This standard is issued under the fixed designation F2724; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method is designed to provide a standardized method to determine the dislocation resistance of mobile-bearing
mobile bearing knee designs with regard to femoral component disassociation and spin-out/spit-out of the mobile bearing insert.
1.2 Although the methodology described does not replicate all physiological loading conditions, it is a means of in-vitro
comparison of mobile bearing knee designs and their ability to resist dislocation of the mobile bearing from the femoral or tibial
components under stated test conditions.
1.3 The test method applies only to mobile bearing total knee designs.
1.4 The values stated in SI units are regarded as standard. The values given in parentheses are mathematical conversions to
inch-pound units that are provided for information only and are not considered standard.
1.5 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 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.
2. Referenced Documents
2.1 ASTM Standards:
F1223 Test Method for Determination of Total Knee Replacement Constraint
3. Terminology
3.1 Definitions:
3.1.1 bearing axis, n—the line connecting the lowest points on both the lateral and medial condyles of the superior surface of the
mobile bearing.
3.1.2 centerline axis, n—a line through the neutral point perpendicular to the bearing axis and in a plane parallel to the plane of
the flat portion of the inferior articulating surface of the mobile bearing at 0° posterior tibial slope.
This test method is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility of Subcommittee
F04.22 on Arthroplasty.
Current edition approved March 15, 2014March 1, 2021. Published April 2014March 2021. Originally approved in 2008. Last previous edition approved in 20082014 as
F2724 – 08. 08 (2014). DOI: 10.1520/F2724-08R14.10.1520/F2724-21.
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volume information, refer to the standard’s Document Summary page on the ASTM website.
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F2724 − 21
3.1.3 mobile bearing (insert), n—the component between fixed femoral and tibial knee components with an articulating surface
on both the inferior and superior sides.
3.1.4 neutral point, n—midpoint of the bearing axis.
3.1.5 spin-out, n—excessive rotation of the bearing component in a rotating platform knee or multi-directional platform knee such
that there is dislocation between the femoral or tibial components and the mobile bearing.
3.1.6 spit-out, n—escape of the bearing component from beneath the femoral component either anteriorly or posteriorly.
3.1.7 total bearing spacing, n—distance between the contact points as given by Test Method F1223.
3.1.8 2-axistwo-axis orthogonal load frame, n—a test machine capable of applying forces and displacements that act at 90° to each
other.
4. Significance and Use
4.1 This test method is designed to provide a standardized method to determine the constraint of mobile-bearing mobile bearing
knee designs with regardsregard to spin-out and spit-out of the mobile bearing.
4.2 Similar to constraint testing of total knees (see Test Method F1223), it is important to note that the test method does not
simulate the soft tissues and laxity of the knee joint, which may be key factors related to the occurrence of spin-out or spit-out.
For instance, a patient with good soft tissue restraints will perhaps require a lower spin-out/spit-out resistance, whereas a patient
with major bone loss or destroyed ligamentous structures will likely require an implant with a higher spin-out/spit-out resistance.
Therefore, the results from the test should be taken into account along with the condition of the patient’s soft tissues to determine
the relative safety for the device.
5. Apparatus and Materials
5.1 AAn engineering analysis should be performed on all sizes of a knee design to justify a “worst case” size for this test. At least
five mobile bearing inserts of that size should be tested. The tibial tray and knee femoral component may be reused for multiple
trials as long as they are not damaged during testing.
5.2 The mobile bearing surfaces shall be lightly coated with bovine serum, olive oil, mineral oil, or deionized waterwater (for
example, reverse osmosis (RO) water, deionized (DI) water, or distilled water) to reduce friction effects during testing.
5.3 A 2-axistwo-axis orthogonal load frame with feedback control shall be used for dislocation testing. The machine must be able
to record force and displacement in both axes.
5.4 Fixtures shall be required to allow for an 80 % medial and 20 % lateral load distribution to be applied through the condyles
of the femoral component.
5.5 During testing, the tibial tray posterior slope and femoral component degree of flexion should be set according to the
recommended surgical alignment.
6. Specimen Preparation
6.1 All components should be inspected prior to testing to ensure that they meet the geometrical and material specifications. The
tibial inserts should
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