1、Designation: F 1440 92 (Reapproved 2002)Standard Practice forCyclic Fatigue Testing of Metallic Stemmed Hip ArthroplastyFemoral Components Without Torsion1This standard is issued under the fixed designation F 1440; the number immediately following the designation indicates the year oforiginal adopti
2、on or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes a method for the fatigue testingof metallic stemm
3、ed femoral components used in hip arthro-plasty. The described method is intended to be used to evaluatethe comparison of various designs and materials used forstemmed femoral components used in the arthroplasty. Thispractice covers procedures for the performance of fatigue testsusing (as a forcing
4、function) a periodic constant amplitudeforce.1.2 This practice applies primarily to one-piece prosthesesand modular components, with head in place such that pros-theses should not have an anterior/posterior bow, and shouldhave a nearly straight section on the distal 50 mm of the stem.This practice m
5、ay require modifications to accommodate otherfemoral stem designs.1.3 The values stated in SI units are to be regarded as thestandard.1.4 For additional information see Refs. (1-5) .2. Referenced Documents2.1 ASTM Standards:E 4 Practices for Force Verification of Testing Machines2E 466 Practice for
6、Conducting Force Controlled ConstantAmplitude Axial Fatigue Tests of Metallic Materials2E 467 Practice for Verification of Constant Amplitude Dy-namic Forces in an Axial Fatigue Testing System2E 468 Practice for Presentation of Constant Amplitude Fa-tigue Test Results for Metallic Materials23. Termi
7、nology3.1 Definitions and Symbols (see Fig. 1(a) and 1(b):3.1.1 cantilever planea plane perpendicular to the line ofload application at the level on the stem where the stembecomes unsupported.3.1.2 distal stem axisthe centerline in the anterior/posterior projection of the most distal 50 mm of the st
8、em.3.1.3 estimated maximum bending momentthe maximumload times the unloaded moment arm.3.1.4 geometric centroid (cantilever plane) the point in across-sectional area of the cantilever plane whose coordinatesare the mean values of the coordinates of all the points in thearea.3.1.5 line of load applic
9、ationthe loading axis of the testmachine.3.1.6 Reference Line L1, distal stem axisthe medial-lateral (M-L) centerline of the most distal 50 mm of stem in theA-P projection.3.1.7 Reference Line L2:3.1.7.1 collared device the plane of the distal side of thecollar in the A-P projection.3.1.7.2 collarle
10、ss devicethe resection plane recommendedfor the device in the A-P projection.3.1.8 Reference Point P1the spherical center of the pros-thesis head.3.1.9 Reference Point P3:1This practice is under the jurisdiction of ASTM Committee F04 on Medical andSurgical Materials and Devices and is the direct res
11、ponsibility of SubcommitteeF04.22 on Arthroplasty.Current edition approved Sept. 15, 1992. Published November 1992.2Annual Book of ASTM Standards, Vol 03.01.FIG. 1 Collared Device1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.9.
12、1 collared device the intersection of the principalaxis of the collar (L2) with the medial surface of the stem in theA-P projection.3.1.9.2 collarless devicethe intersection of the resectionplane (L2) with the medial surface of the stem in the A-Pprojection.3.1.10 Reference Point P4the distal tip of
13、 the stem.3.1.11 Reference Point P63 the intersection of the canti-lever plane with the medial surface of the stem in the A-Pprojection.3.1.12 R valuethe R value is the ratio of the minimumforce to the maximum force.R 5minimum forcemaximum force3.1.13 Stem Reference Angle Xthe angle between the stem
14、reference line and the line of load application.3.1.14 stem reference linea line passing through Refer-ence Point P6 and the center of the prosthesis head (P1).3.1.15 supported stem lengththe vertical distance be-tween the distal tip of the stem (P4) and the cantilever plane.3.1.16 unloaded moment a
15、rmthe perpendicular distancebetween the line of load application and the geometric centroidof the stem cross section at the cantilever plane.3.1.17 unsupported stem lengththe vertical distance be-tween Point P3 and the cantilever plane.3.2 See Figs. 1 and 2.4. Significance and Use4.1 This practice c
16、an be used to describe the effects ofmaterials, manufacturing, and design variables on the fatigueresistance of metallic stemmed femoral components subjectedto cyclic loading for relatively large numbers of cycles. Therecommended test assumes a “worst case situation whereproximal support for the ste
17、m has been lost. It is alsorecognized that for some materials the environment may havean effect on the response to cyclic loading. The test environ-ment used and the rationale for the choice of that environmentshould be described in the report.4.2 It is recognized that actual in vivo loading conditi
18、ons arenot constant amplitude. However, there is not sufficient infor-mation available to crate standard load spectrums for metallicstemmed femoral components. Accordingly, a simple periodicconstant amplitude force is recommended.4.3 In order for fatigue data on femoral stems to be usefulfor compari
19、son, it must be reproducible among differentlaboratories. Consequently, it is essential that uniform proce-dures be established.5. Specimen Selection5.1 The specimen selection should have the same geometryas the final finished product, and the stem should be in the finalfinished condition.6. Apparat
20、us6.1 The specimen shall be constrained by a suitable groutingagent within a rigid cavity. A common grouting agent used ispoly methyl methacrylate (PMMAbone cement) that ispolymerized in place. The minimum thickness of the groutingagent should be 1 cm. Although bone cement is the recom-mended grouti
21、ng agent, other material may be used provided itdoes not chemically or mechanically interact with the testspecimen.6.2 The test fixtures shall be constructed so that the line ofload application is in the implant anterior/posterior symmetryplane of the supported portion of the stem.6.3 The test fixtu
22、res shall be constructed so that the line ofload application passes through the ball center.6.4 A ball- or roller-bearing low-friction mechanism shallbe included in the loading apparatus to minimize loads notperpendicular to the cantilever plane. An example of such amechanism is included in Appendix
23、 X1.7. Equipment Characteristics7.1 The action of the machine should be analyzed to ensurethat the desired form and periodic force amplitude is main-tained for the duration of the test. (See Practice E 467.)7.2 The test machine should have a load monitoring systemsuch as the transducer mounted in li
24、ne with the specimen. Thetest loads should be monitored continuously in the early stagesof the test and periodically thereafter to ensure the desired loadcycle is maintained. The varying load as determined bysuitable dynamic verification should be maintained at all timesto within 62 % of the maximum
25、 force being used.8. Procedure8.1 Specimen Test OrientationThe angle between thedistal stem axis and the line of load application shall be 10 61 %. An example of a method to accomplish mounting thestem at the desired angle is given in Appendix X2.3The reference points and lines are consistent with t
26、he Proposed StandardSpecification for Cementable Total Hip Prostheses with Femoral Stems. Thereference points “P2” and “P5” in that proposed specification are not relevant to thispractice. Consequently, they are not used in this practice.FIG. 2 Collarless DeviceF 1440 92 (2002)28.2 Specimen Mounting
27、:8.2.1 Maintain the stem Reference Angle X within a rangeof 61 over a test group.8.2.2 Maintain the unsupported stem length at 62 mm.8.2.3 No relative motion between the prosthesis and thegrouting agent is permitted during hardening of the groutingagent.8.2.4 The surface of the grouting agent at the
28、 cantileverplane shall be approximately level and perpendicular to the lineof load application.8.2.5 An example of a technique for setting a specimen inthe grouting agent in the correct orientation is given inAppendix X2.8.3 Test Frequency Run all tests at a test frequency of 30Hz or less.8.4 R Valu
29、eRun all tests with an R value of 10.0.48.5 Measure the unsupported stem length, stem referenceangle, and moment arm for each test specimen prior to testing.A possible means would be to use a shadowgraph of theanterior posterior projection as shown in Fig. 1.8.6 Estimate the amount of horizontal def
30、lection of the headin response to the periodic forcing function one time after thebeginning of each test. Possible methods included dial gages,optical micrometers, or linear scales viewed with a strobe lightto slow the apparent motion of the deflection.9. Test Termination9.1 Continue the test until
31、the specimen fails or until apredetermined number of cycles has been applied to thespecimen. Failure should be defined as a complete separation,or exceeding of a deflection limit on a test machine. Inreporting results, state the criteria selected for defining failureand the number of cycles shown as
32、 the predetermined runout ofthe test. Discard the data for a specific sample if the groutingagent fractured prior to test completion.10. Report10.1 Report the fatigue test specimens, procedures, andresults in accordance with Recommended Practice E 468.10.2 In addition, report the following parameter
33、s: StemReference Angle X, supported stem length, maximum force, Rvalue, specimen material, cycles to failure, location of fracturesin relation to the cantilever plane, average dimensions of thestem cross section in the cantilever plane, grouting agent, testenvironment, and test frequency.11. Precisi
34、on and Bias11.1 The precision and bias of this practice is being estab-lished.512. Keywords12.1 arthroplasty; femoral components; hip arthroplasty;metallic stemmed femoral components; orthopaedic medicaldevices4In strict terms, since the force applied to the head is compressive, the maximumforce is
35、the smallest negative amplitude. Consequently the R value is 10 when thenegative signs cancel each other. In terms of applied bending moment at thecantilever plane, the R value would be 0.15Test results that can be used to establish precision and bias are solicited.F 1440 92 (2002)3APPENDIXES(Nonman
36、datory Information)X1. EXAMPLE OF A LOW-FRICTION MECHANISMX1.1 See Fig. X1.1.X2. EXAMPLE PROSTHESIS MOUNTING PROCEDUREX2.1 A drawing or shadowgraph of the prosthesis should beavailable before mounting to establish the angular relationshipbetween the distal stem axis and the stem reference angle.X2.2
37、 A gripping device as illustrated in Fig. X2.1 or aringstand and test tube holder can be used to grip the head ofthe subject prosthesis.X2.3 The prosthesis is held by the head permitting thedistal tip to rest on a flat surface. The angle jig is positionedwith the distal stem in the notch. The stem i
38、s adjusted so thatit is centered in the notch of the angle jig. This will orient thedistal stem at approximately 10 deg to the line of loadapplication. The head is now firmly gripped to maintain theangular orientation of the stem.X2.4 The angle jig can be removed and the prosthesismounted at the app
39、ropriate depth in an appropriate specimenholder.X2.5 Grouting material can be placed around the testprosthesis into the specimen holder and allowed to harden.FIG. X1.1 Example of a Low Friction MechanismF 1440 92 (2002)4X2.6 After hardening of the grouting agent the grip on thehead of the prosthesis
40、 is released and a shadowgraph may beprepared of the profile of the test specimen/specimen holderassembly.X2.7 A second adjustable stop may be added below the gripand adjusted to rest against the medial surface of an appropri-ately oriented prosthesis to facilitate repeatable mounting ofthe test gro
41、up.X3. RATIONALEX3.1 Fracture of femoral stems in THA has been a problemin clinical application. The stem design, PMMA support,quality of bone, and other features contribute to stem fracture.One recognizable mode of failure is with the distal portion ofthe stem firmly anchored, while medial proximal
42、 support islost. As the body loads are applied through the head of theprosthesis, significant stem stresses can result at the area wherethe cement is still firmly anchored. Because it is believed thatthis proximal cement breakdown model is the primary reasonbehind fracture of the femoral stems, this
43、 simplified model waschosen for the fatigue testing of actual stems. There are someproblems with the proposed simplified model. The worst caseassumes that proximal cement breakdown has already oc-curred. It does not address any features of a THA system thatmight help prevent cement breakdown or any
44、features that aidin placing the femoral component in an optimal position withgood cement support. While the latter approach is desirable,the test described can give information on the relative fatiguestrengths.X3.2 In 8.1 there is no specification of the number of cyclesfor test runout. The fundamen
45、tal idea behind this type of test isthat the number of cycles to runout represents a limiting pointbeyond which the material will not fracture no matter howmany more cyclic loads are applied. This is referred to as afatigue limit. However, in real life most materials do notpossess a true fatigue lim
46、it. Consequently, a compromise mustbe made between the amount of testing, (the number of testcycles) and the relationship of the test to actual deviceperformance and device life. Since most of these tests areplotted and evaluated on a semi-log or log-log plot, a typicalrunout point is often ten mill
47、ion cycles. Doubling or triplingthe number of test cycles to twenty or thirty million contributesonly a small amount to the trend analysis on the log scale, butit doubles or triples the length of the test. In Europe five millioncycles has been used as a runout value for some stem tests.X3.3 This tes
48、t is a cantilever beam bend test. In a cantileverbeam bend test the load point will tend to deflect in thedirection of the applied load, the amount of deflection depend-ing on the elasticity of the test sample With this test the headof the prosthesis is the cantilever load point. Since the direction
49、of the load also applies a compressive force down the stem,only the vector portion of the force, perpendicular to theprosthesis long axis, will contribute to the beam deflection.That contribution of beam bending will deflect the head to theside. This motion effectively increases the bending momentarm. This motion must be permitted. If the head is not allowedFIG. X2.1 Apparatus for Gripping the Test Specimen WhileEmbedding it in the Correct OrientationF 1440 92 (2002)5to deflect in a near frictionless manner the portion of the testfixture that prevents th
