ASTM F1612-95(2000)
(Practice)Standard Practice for Cyclic Fatigue Testing of Metallic Stemmed Hip Arthroplasty Femoral Components with Torsion
Standard Practice for Cyclic Fatigue Testing of Metallic Stemmed Hip Arthroplasty Femoral Components with Torsion
SCOPE
1.1 This practice covers a method for the fatigue testing of metallic stemmed femoral components used in hip arthroplasty. The described method is intended to be used for evaluation in comparisons of various designs and materials used for stemmed femoral components used in the arthroplasty. This practice covers procedures for the performance of fatigue tests using (as a forcing function) a periodic constant amplitude force.
1.2 This practice applies primarily to one-piece prostheses and femoral stems with modular heads, with the head in place. Such prostheses should not have an anterior-posterior A-P bow or a medial-lateral M-L bow, and they should have a nearly straight section on the distal 50 mm of the stem. This practice may require modifications to accommodate other femoral stem designs.
1.3 The values stated in SI units are to be regarded as the standard.
1.4This 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:F1612–95 (Reapproved 2000)
Standard Practice for
Cyclic Fatigue Testing of Metallic Stemmed Hip Arthroplasty
Femoral Components with Torsion
This standard is issued under the fixed designation F1612; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope ISO 7206-3 (1988) Stem Test
1.1 This practice covers a method for the fatigue testing of
3. Terminology (see Fig. 1 Fig. 2)
metallicstemmedfemoralcomponentsusedinhiparthroplasty.
3.1 Definitions of Terms Specific to This Standard:
The described method is intended to be used for evaluation in
3.1.1 cantilever plane—a plane perpendicular to the line of
comparisons of various designs and materials used for
load application at the level on the stem at which the stem
stemmed femoral components used in the arthroplasty. This
becomes unsupported.
practice covers procedures for the performance of fatigue tests
3.1.2 distal stem axis—the centerline in the A-P projection
using (as a forcing function) a periodic constant amplitude
and the M-L projection of the most distal 50 mm of the stem.
force.
3.1.3 estimated maximum bending moment—the maximum
1.2 This practice applies primarily to one-piece prostheses
compressive load times the unloaded moment arm.
and femoral stems with modular heads, with the head in place.
3.1.4 geometric centroid (cantilever plane)— the point in a
Suchprosthesesshouldnothaveananterior-posteriorA-Pbow
cross-sectional area of the cantilever plane whose coordinates
or a medial-lateral M-L bow, and they should have a nearly
arethemeanvaluesofthecoordinatesofallofthepointsinthe
straight section on the distal 50 mm of the stem. This practice
area.
mayrequiremodificationstoaccommodateotherfemoralstem
3.1.5 line of load application—the loading axis of the test
designs.
machine.
1.3 The values stated in SI units are to be regarded as the
3.1.6 R value—the ratio of the minimum force to the
standard.
maximum force,
1.4 This standard does not purport to address all of the
minimum force
safety concerns, if any, associated with its use. It is the
R 5
maximum force
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3.1.7 Reference Line L1:
bility of regulatory limitations prior to use.
3.1.7.1 distal stem axis—the M-L centerline of the most
distal 50 mm of stem in the A-P projection.
2. Referenced Documents
3.1.8 Reference Line L2:
2.1 ASTM Standards:
3.1.8.1 collared device—the plane of the distal side of the
E4 Practices for Force Verification of Testing Machines
collar in the A-P projection.
E466 Practice for Constant Amplitude Axial Fatigue Tests
3.1.8.2 collarless device—theresectionplanerecommended
of Metallic Materials
for the device in the A-P projection.
E467 Practice for Verification of Constant Amplitude Dy-
3.1.9 Reference Point P1—the spherical center of the pros-
namic Loads in an Axial Load Fatigue Testing Machine
thesis head.
E468 Practice for Presentation of Constant Amplitude Fa-
3.1.10 Reference Point P3:
tigue Test Results for Metallic Materials
3.1.10.1 collared device—the intersection of the principal
E1150 Definitions of Terms Relating to Fatigue
axisofthecollar(L2)withthemedialsurfaceofthesteminthe
2.2 ISO Document:
A-P projection.
3.1.10.2 collarless device—the intersection of the resection
plane (L2) with the medial surface of the stem in the A-P
ThispracticeisunderthejurisdictionofASTMCommitteeF04onMedicaland
projection.
Surgical Materials and Devicesand is the direct responsibility of Subcommittee
3.1.11 Reference Point P4—the distal tip of the stem.
F04.22on Arthroplasty.
Current edition approved Aug. 15, 1995. Published December 1995.
Annual Book of ASTM Standards, Vol 03.01.
Available from American National Standards Institute, 11 W. 42nd St., 13th
Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F1612
FIG. 2 1(b) Collarless Device, M-L Projection
FIG. 1 1(a) Collared Device, M-L Projection
4. Significance and Use
4.1 This practice can be used to describe the effects of
3.1.12 Reference Point P6 — the intersection of the canti-
materials, manufacturing, and design variables on the fatigue
lever plane with the medial surface of the stem in the A-P
resistance of metallic stemmed femoral components subjected
projection.
to cyclic loading for relatively large numbers of cycles. The
3.1.13 stem reference angles—Since the distal stem axis is
recommended test assumes a worst case situation in which
obscurred by the grouting agent after preparation of the test
proximal support for the stem has been lost. It is also
sample,thestemreferenceanglesaretobeusedtomeasurethe
recognized that, for some materials, the environment has an
repeatability of the stem orientation.They may also be used to
effect on the response to cyclic loading (see section 12.7). The
estimate the actual orientation of the distal stem to the line of
test environment used and rationale for the choice of that
load application if the stem geometry is well known.
environment should be described in the test report.
3.1.13.1 X (M-L)—the angle between the stem reference
4.2 Itisrecognizedthatactualinvivoloadingconditionsare
line and line of load application in the M-L projection.
not constant amplitude. However, sufficient information is not
3.1.13.2 X (A-P)—theanglebetweenthestemreferenceline
available to create standard load spectrums for metallic
and line of load application in the M-L and A-P projections.
stemmed femoral components. A simple periodic constant
3.1.14 stem reference line—a line passing through Refer-
amplitude force is accordingly recommended.
ence Point P6 and the center of the prosthesis head (P1).
5. Purpose
3.1.15 supported stem length—the vertical distance be-
tween the distal tip of the stem (P4) and cantilever plane. 5.1 In order for fatigue data on femoral stems to be useful
for comparison, it must be reproducible among different
3.1.16 unloaded moment arm—the vector sum of the per-
pendicular distance between the line of load application and laboratories. It is consequently essential that uniform proce-
dures for testing and reporting test data be established.
geometric centroid of the stem cross section at the cantilever
plane in the A-P and M-L projections.
6. Apparatus
3.1.17 unsupported stem length—the vertical distance be-
6.1 Thespecimenshallbeconstrainedbyasuitablegrouting
tween Point P3 and the cantilever plane.
agent within a rigid cavity. A common grouting agent used is
polymethyl methacrylate (PMMA, bone cement). The mini-
mumthicknessofthegroutingagentshouldbe1cm.Although
The reference points and lines are consistent with the proposed Specification
bone cement is the recommended grouting agent, other mate-
for CementableTotal Hip Prostheses with Femoral Stems.The Reference Points P2
rial may be used, provided that it does not alter the test
and P5 in that specification are not relevant to this practice. Consequently, they are
not used in this practice. specimen chemically or mechanically.
F1612
6.2 The test fixtures shall be constructed so that the line of 9. Procedure
load application is in the implant A-P symmetry plane of the
9.1 Specimen Test Orientation—The angle between the
supported portion of the stem (Fig. 3).
distal stem axis and the line of load application in the M-L
6.3 The test fixtures shall be constructed so that the line of
projection shall be 10 6 1° (Fig. 1 Fig. 2)), and the angle
load application passes through the ball center.
between the distal stem axis and the line of load application in
6.4 Aballorrollerbearing,low-frictionmechanismshallbe
the A-P projection shall be 9 6 1° (Fig. 3). An example of a
included in the loading apparatus to minimize loads not
method of accomplishing mounting the stem at the desired
perpendicular to the cantilever plane. An example of such a
angle is given in Appendix X1.
mechanism is included in Appendix X2.
9.2 Specimen Mounting:
9.2.1 Maintain the stem reference angles X (M-L) and X
7. Specimen Selection
(A-P) within a range of 61° over a test group.
7.1 The specimen selected should have the same geometry
9.2.2 Maintain the unsupported stem length within 62 mm.
asthefinalfinishedproduct,andthestemshouldbeinthefinal 9.2.3 Do not permit any relative motion between the pros-
finished condition.
thesis and grouting agent during hardening of the grouting
7.2 The head of the prothesis should have the same geom- agent.
etry and surface finish as the final finished product, unless it 9.2.4 Keepthesurfaceofthegroutingagentatthecantilever
can be demonstrated that differences in the condition of the planeapproximatelylevelandperpendiculartothelineofload
head have no effect on the fatigue response of the stem in this application.
test.
9.2.5 An example of a technique for setting a specimen in
7.3 The length of the neck of the prosthesis contributes to the grouting agent in the correct orientation is given in
themagnitudeofthemaximumbendingmoment.Thelengthof
Appendix X1.
neck(orheadoffset)shouldbethelongestpossiblethatwillbe 9.3 Test Frequency—Run all tests at a test frequency of 30
used with the femoral stem being evaluated. This will inher-
Hz or less (see section 12.8).
ently maximize the maximum bending moment. 9.4 R Value—Run all tests with an R value of 10.0.
9.5 Measure the unsupported stem length, stem reference
8. Equipment Characteristics
angle, and moment arm for each specimen prior to testing. A
possible means would be to use a shadowgraph of the A-P
8.1 The action of the machine should be analyzed to ensure
projection as shown in Fig. 1 Fig. 2 Fig. 3.
that the desired form and periodic force amplitude is main-
9.6 Measuretheamountofhorizontaldeflectionofthehead
tained for the duration of the test. (see Practice E467).
inboththeM-LandA-Pprojectionsinresponsetotheperiodic
8.2 The test machine should have a load monitoring system
forcing function one time after the beginning of each test (see
such as the transducer mounted in line with the specimen. The
section 12.9).
test loads should be monitored continuously in the early stages
of the test and periodically thereafter to ensure that the desired
10. Test Termination
load profile is maintained. The varying load as determined by
10.1 Continue the test until the specimen fails or a prede-
suitable dynamic verification should be maintained at all times
termined number of cycles has been applied to the specimen.
to within 62% of the largest compressive force being used.
Specimenfailureshouldbedefinedasacompleteseparationof
the specimen, or exceeding of a deflection limit on a test
machine. In reporting the results, state the criteria selected for
defining specimen failure and the number of cycles shown as
the predetermined runout of the test. Discard the data for a
specific sample if the grouting agent fails prior to test comple-
tion.
11. Report
11.1 Report the fatigue test specimens, procedures, and
results in accordance with Practice E468.
11.2 In addition, report the following parameters: stem
reference angles X (M-L) and X (A-P), unsupported stem
length, supported stem length, largest compressive force, R
value, specimen material, cycles to failure, estimated maxi-
mum bending moment, location of fractures in relation to the
Instrictterms,sincetheforceappliedtotheheadiscompressive,themaximum
force is the largest algebraic value. The R value is consequently 10 when the
negative signs cancel each other.As a numeric example, assume a test is conducted
atapeakloadof3000N(−3000).Theleastcompressiveloadwouldbe10%ofthat,
or 300 N (−300). The R value would be−3000/−300, or 10. The R value would be
FIG. 3 Collared or Collarless Device, A-P Projection 0.1 in terms of applied bending moment at the cantilever plane.
F1612
cantilever plane, average dimensions of the stem cross section
in the cantilever plane, grouting agent, test environment, test
frequency, head/neck offset of the stem (neck length), and
deflection limit used to cut off testing (see 10.1).
12. Precision and Bias
12.1 The precision and bias of this practice is being
established.
APPENDIXES
(Nonmandatory Information)
X1. EXAMPLE PROSTHESIS MOUNTING PROCEDURE
X1.1 Adrawingorshadowgraphoftheprosthesisshouldbe ringstand and test tube holder can be used to grip the head of
available before mounting to establish the angular relationship the subject prosthesis.
between the distal stem axis and stem reference angle.
X1.3 The prosthesis is held by the head permitting the
X1.2 A gripping device, as illustrated in Fig. X1.1, or a
distal tip to rest on a flat surface. The angle jig illustrated in
Fig. X1.2 is positioned with the distal stem in the notch. The
stem is adjusted so that it is centered in the notch of the angle
jig. This will orient the distal stem at approximately 10° to the
line of load application. The head is now gripped firmly to
maintain the angular orientation of the stem.
X1.4 The angle jig can be removed and the prosthesis
mounted at the appropriate depth in an appropriate specimen
holder.
X1.5 Grouting material can be placed around the test
prosthesis into the specimen holder and permitted to harden.
X1.6 Thegripontheheadoftheprosthesisisreleasedafter
hardening of the grouting agent, and a shadowgraph may be
prepared of the profile of the test specimen and specimen
holder assembly.
X1.7 Asecondadjustablestopmaybeaddedbelowthegrip
and adjusted to rest against the medial surface of an appropri-
ately oriented prosthesis to facilitate repeatable mounting of
FIG. X1.1 Example of a Low-Friction Mechanism the test group.
F1612
FIG. X1.2 Apparatus for Gripping the Test Specimen While
Embedding it in the Correct Orientation
X2. RATIONALE
X2.1 Thebreakageoffemoralstemsinhiparthroplastyhas X2.3 Thispracticeattemptstomodelsimplytheorientation
occurred in clinical application. The stem design, PMMA of the stemmed femoral component in relation to the peak
support, quality of bone, and other features contribute to stem loads that are applied in the human body. To accomplish this,
fracture. One recognizable mode of breakage is with the distal thedistalstemwillhaveananatomicorientationtotheapplied
portion of the stem anchored firmly, while medial proximal load in both the M-LandA-Pplane of the prosthesis. Because
support is lost.As the body loads are applied through
...
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