ASTM F3334-19

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.
Designation: F3334 − 19
Standard Practice for
Finite Element Analysis (FEA) of Metallic Orthopaedic Total
Knee Tibial Components
This standard is issued under the fixed designation F3334; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice establishes requirements and consider-
F1800Practice for Cyclic Fatigue Testing of Metal Tibial
ations for the numerical simulation of metallic orthopaedic
Tray Components of Total Knee Joint Replacements
total knee tibial components using Finite Element Analysis
(FEA) techniques for the estimation of stresses and strains.
3. Significance and Use
This practice is only applicable to stresses below the yield
strength, as provided in the material certification.
3.1 This practice is applicable to the calculation of stresses
seen on a knee tibial component when loaded in a manner
1.2 Purpose—This practice establishes requirements and
described in this practice.This practice can be used to identify
considerations for the development of finite element models to
the worst-case size for a particular implant. When stresses
be used in the evaluation of metallic orthopaedic total knee
calculated using this FEA method were compared to the
tibial component designs for the purpose of prediction of the
stresses measured at two locations on the tibial tray using
static implant stresses and strains. This procedure can be used
physical strain gauging techniques performed at one
for worst-case assessment within a series of different implant
laboratory, the difference observed was -6.8 % at one location
sizes of the same implant design to reduce the physical test
(withthestraingaugesreportingthehigherstress)and3.1%at
burden. Recommended procedures for performing model
the other location (with the FEA method reporting a higher
checks and verification are provided as an aid to determine if
stress).Thisdifferenceshouldbeconsideredwhendetermining
the analysis follows recommended guidelines. Finally, the
the worst-case size(s) of the same implant design.
recommended content of an engineering report covering the
3.2 Theloadingoftibialtraydesignsinvivowill,ingeneral,
mechanical simulation is presented.
differ from the loading defined in this practice. However, this
1.3 Limits—This practice is limited in discussion to the
practice is designed to allow for comparisons between the
static structural analysis of metallic orthopaedic total knee
fatigue performance of different metallic tibial component
tibial components (which excludes the prediction of fatigue
designs, when tested under similar conditions.
strength).
4. System Geometry
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4.1 Finite element models are based on a geometric repre-
responsibility of the user of this standard to establish appro-
sentation of the device being studied. The source of the
priate safety, health, and environmental practices and deter-
geometricdetailscanbeobtainedfromdrawings,solidmodels,
mine the applicability of regulatory limitations prior to use.
preliminary sketches, or any other source consistent with
defining the model geometry. In building the finite element
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard- model, certain geometric details may be omitted from the
orthopaedic implant geometry shown in the Computer Aided
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom- Design (CAD) model if it is determined that they are not
relevant to the intended analysis. Engineering judgment shall
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. be exercised to establish the extent of geometric simplification
and shall be justified.
ThistestmethodisunderthejurisdictionofASTMCommitteeF04onMedical
andSurgicalMaterialsandDevicesandisthedirectresponsibilityofSubcommittee For referenced ASTM standards, visit the ASTM website, www.astm.org, or
F04.22 on Arthroplasty. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Aug. 1, 2019. Published September 2019. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/F3334-19. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F3334 − 19
4.2 Itismostappropriatetoconsiderthe“worst-case”stress for determining the position of the load point described in
condition for the orthopaedic implant being simulated. The clause 6.6 of Practice F1800. Locate the cylinder in the SI
“worst-case”shallbedeterminedfromallrelevantengineering direction (refer to Fig. 2) such that the cylinder intersects the
considerations, such as tibial component geometry and dimen- superiorsurfaceofthetibialcomponent.Createanintersecting
sions. If finite element analysis is being used for determining circular contour onto the superior face that defines the periph-
the worst case, then the worst-case size may not be known. It ery of the load footprint, and then delete the cylinder from the
maybenecessarytorunseveralsizesinordertodeterminethe model. No solid material should be added to or removed from
worst case. If the FEA results do not conclusively determine the tibial component model by the operation. Apply a unit (1
the worst-case configuration, a rationale should be included N) load uniformly in the inferior direction over the load
(e.g., additional analysis or physical testing) to justify the footprint(refertoFig.2).Analternativeloadmagnitudecanbe
worst-case size. applied, if that load magnitude does not result in developing
stresses above the yield strength of the material. The use of
5. Material Properties
alternative loading conditions shall be justified.
5.1 The required material properties for input into a linear,
6.3 It is recognized that the loading conditions in this
elastic FEA model for the calculation of strains and displace-
practice will not be identical to those of Practice F1800.
ment are modulus of elasticity (E) and Poisson’s ratio (ν).
However, the difference in loading conditions (e.g., load
These values can be obtained from material certification data.
applicationdifferences,fixationdifferences)shouldnotsignifi-
It should be noted that the fatigue test described in Practice
cantly affect identification of the “worst-case” stress condition
F1800 is run under load control; the corresponding FEAshall
and implant size for subsequent bench testing, which is the
be run under an applied force. When the FEAis run under an
primary objective of this practice. When subsequent physical
appliedforce,themodulusofelasticitywillnotaffectthestress
testing per Practice F1800 is performed, comparison of the
calculations under small displacement theory (assuming a
physical test results (i.e., location of tray fracture) should be
monolithiccomponent),butwillaffectdisplacementandstrain.
comparedtotheFEAtestresultstodetermineiftherewereany
The influence of Poisson’s ratio on the stress calculations is
significantdifferences.Ifso,thereasonforthisdifferenceshall
negligible.
be evaluated, necessary adjustments shall be made to the
physical test fixtures or finite element model, and, depending
5.2 Ensure that material property units are consistent with
on the results of the analysis, testing of additional components
geometric units in the CAD model. SI units are the preferred
may be necessary.
units of measurement.
6.4 Ensure that load units are consistent with material
6. Loading Conditions
property units.
6.1 The loading location and orientation of the knee tibial
7. Boundary Conditions
component shall be guided by the loading location and
boundaryconditionsdescribedbelow.Theloadinglocationand 7.1 Either the medial or lateral half of the tibial component
orientation are consistent with Practice F1800. The area of shall be fully encased in a CAD-generated block with bone
interest is the location of the maximum principal stress and cement material properties. This methodology has been dem-
other design-specific critical regions (e.g., sharp corners, onstrated to minimize boundary condition-induced stress
threads, locking mechanisms). artifacts, which develop along the protruding inferior tibial
component edge when a stiff block is used. A subtractive
6.2 In the medial-lateral (ML)/anterior-posterior (AP) plane
Boolean operation (i.e., removing tibial component volume
(refer to Fig. 1), locate a 6.35 mm (0.25 in.) diameter solid
from the solid block volume) is commonly used for this step.
cylinder (actual dimensions of the spacer may vary as smaller
tibial tray designs may require a smaller diameter disk) on the 7.2 Considering reference tibial component bounding box
superior surface of the knee tibial component, per the method dimensions AP , ML , and SI (refer to Fig. 1), the bone
tc tc tc
NOTE 1—SI excludes the stem length for stemmed designs.
tc
FIG. 1 Tibial Component Bounding Box
F3334 − 19
FIG. 2 Loading and Boundary Condition Dimensions
cementblockdimensions AP , ML ,and SI (refertoFig. refinement in the critical stress regions is used to demonstrate
box box box
2)shallhavetheminimumvaluesofAP =1.5×AP ,ML solution convergence. This allows the error associated with
box tc box
= 0.75 × ML , and SI = 3.0 × SI . For stemmed designs, subsequent models to be estimated. The method used to
tc box tc
calculate SI = 3.0 × SI + stem length. These dimensions demonstrate mesh convergence (in analysis cases where it is
box tc
have been demonstrated to minimize any constraint-induced notperformeddirectlyontothemodelbeinganalyzed)shallbe
stressartifacts(asdefinedbelow).Theencasedhalfofthetibial documented in the FEA report. It is recommended that a
component shall be centrally positioned in the AP and SI minimumofthreelevelsofmeshrefinementbeperformedand
directions within the block. In the ML direction, the tibial amodelconvergenceof≤5% bedemonstratedonthequantity
componentshallbepositionedsuchthattheblockverticalface of interest (see 8.6) and at all regions of interest. A stress
thatisclosesttotheloadlocationisalignedwiththecenterline convergence of >5 % shall be justified based on the context of
of the tibial component, or along the AP centerline of the use.
central keel or other prominence, when applicable.
8.4 The choice of element type is left to the analyst;
7.3 Merged nodes or bonded contact between the bone however, it is recommended for analysis of a knee tibial
cement block and tibial component shall be used to bond the component that tetrahedral or hexahedral elements be used. If
tibial component to the block along their shared surfaces. tetrahedral elements are considered, use of 4-noded elements
shouldbeavoidedtopreventstressandstrainincompatibilities
7.4 The top and bottom surfaces of the cement block shall
across elements. Additionally, the linear, 4-noded tetrahedron
be fixed in all three translational degrees of freedom (refer to
element is a constant strain element.This means that displace-
Fig. 2).
ment interpolation is linear and the corresponding stresses and
7.5 Theuseofalternativetibialcomponentconstraintsshall
strains are constant within any element. Therefore, a very
be justified.
refined mesh is required around locations where high stress/
strain gradients are present when utilizing these elements.
8. Analysis
When using elements that are not directly identified in this
8.1 The analysis and modeling system, programs, or soft-
practice, documentation that demonstrates their validity shall
ware used for the finite element model creation and analysis
be provided in the FEA report.
should be capable of fully developing the geometric features
8.5 The finite element results should be examined to ensure
andidealizingtheloadingandboundaryconditionenvironment
that the geometrical models of the implant, boundary condi-
of the orthopaedic implant. An engineering justification shall
tions and applied loads have been appropriately defined in the
beprovidedtosupportanyassumptionsand/orsimplifications.
analysis to properly represent the behavior of the in vitro test
8.2 The finite element mesh can be created using automatic
condition.
meshing, manual meshing, or a combination of the two
8.6 The primary measure of interest is the maximum (first)
techniques. The overriding consideration is that the type, the
principalstressgeneratedbyaunitload(refertoFig.3andFig.
size, and the shape of the elements used must be able to
4). A secondary measure of interest is the von Mises stress at
simulate the expected behavior without significant numerical
the location of maximum (first) principal stress generated by a
limitation or complication. Check the element quality by
unit load. If other stress values are used, their validi
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