ASTM F1714-96(2008)
(Guide)Standard Guide for Gravimetric Wear Assessment of Prosthetic Hip Designs in Simulator Devices
Standard Guide for Gravimetric Wear Assessment of Prosthetic Hip Designs in Simulator Devices
SIGNIFICANCE AND USE
This guide uses a weight-loss method of wear determination for the polymeric components used with hip joint prostheses, using serum or demonstrated equivalent fluid for lubrication, and running under a dynamic load profile representative of the human hip-joint forces during walking (1,2). The basis for this weight-loss method for wear measurement was originally developed (3) for pin-on-disk wear studies (see Practice F 732) and has been extended to total hip replacements (4,5) femoral-tibial knee prostheses (6), and to femoropatellar knee prostheses (6,7).
While wear results in a change in the physical dimensions of the specimen, it is distinct from dimensional changes due to creep or plastic deformation, in that wear generally results in the removal of material in the form of polymeric debris particles, causing a loss in weight of the specimen.
This guide for measuring wear of the polymeric component is suitable for various simulator devices. These techniques can be used with metal, ceramic, carbon, polymeric, and composite counter faces bearing against a polymeric material (for example, polyethylene, polyacetal, and so forth). This weight-loss method, therefore, has universal application for wear studies of total hip replacements that feature polymeric bearings. This weight-loss method has not been validated for high-density material bearing systems, such as metal-metal, carbon-carbon, or ceramic-ceramic. Progressive wear of such rigid bearing combinations generally has been monitored using a linear, variable-displacement transducers or by other profilometric techniques.
SCOPE
1.1 This guide describes a laboratory method using a weight-loss technique for evaluating the wear properties of materials or devices, or both, which are being considered for use as bearing surfaces of human-hip-joint replacement prostheses. The hip prostheses are evaluated in a device intended to simulate the tribological conditions encountered in the human hip joint, for example, use of a fluid such as bovine serum, or equivalent pseudosynovial fluid shown to simulate similar wear mechanisms and debris generation as found in vivo, and test frequencies of 1 Hz or less.
1.2 Since the hip simulator method permits the use of actual implant designs, materials, and physiological load/motion combinations, it can represent a more physiological simulation than basic wear-screening tests, such as pin-on-disk (see Practice F 732) or ring-on-disk (see ISO 6474).
1.3 It is the intent of this guide to rank the combination of implant designs and materials with regard to material wear-rates, under simulated physiological conditions. It must be recognized, however, that there are many possible variations in the in vivo conditions, a single laboratory simulation with a fixed set of parameters may not be universally representative.
1.4 The reference materials for the comparative evaluation of candidate materials, new devices, or components, or a combination thereof, shall be the wear rate of extruded or compression-molded, ultra-high molecular weight (UHMW) polyethylene (see Specification F 648) bearing against standard counter faces [stainless steel (see Specification F 138); cobalt-chromium-molybdenum alloy (see Specification F 75); thermomechanically processed cobalt chrome (see Specification F 799); alumina ceramic (see Specification F 603)], having typical prosthetic quality, surface finish, and geometry similar to those with established clinical history. These reference materials will be tested under the same wear conditions as the candidate materials.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: F1714 − 96(Reapproved 2008)
Standard Guide for
Gravimetric Wear Assessment of Prosthetic Hip Designs in
Simulator Devices
This standard is issued under the fixed designation F1714; 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
1.1 This guide describes a laboratory method using a
2.1 ASTM Standards:
weight-loss technique for evaluating the wear properties of
D883Terminology Relating to Plastics
materials or devices, or both, which are being considered for
F75Specification for Cobalt-28 Chromium-6 Molybdenum
use as bearing surfaces of human-hip-joint replacement pros-
Alloy Castings and Casting Alloy for Surgical Implants
theses.Thehipprosthesesareevaluatedinadeviceintendedto
(UNS R30075)
simulate the tribological conditions encountered in the human
F86Practice for Surface Preparation and Marking of Metal-
hip joint, for example, use of a fluid such as bovine serum, or
lic Surgical Implants
equivalent pseudosynovial fluid shown to simulate similar
F136 Specification for Wrought Titanium-6Aluminum-
wear mechanisms and debris generation as found in vivo, and
4VanadiumELI(ExtraLowInterstitial)AlloyforSurgical
test frequencies of 1 Hz or less.
Implant Applications (UNS R56401)
1.2 Sincethehipsimulatormethodpermitstheuseofactual
F138 Specification for Wrought 18Chromium-14Nickel-
implant designs, materials, and physiological load/motion
2.5MolybdenumStainlessSteelBarandWireforSurgical
combinations, it can represent a more physiological simulation
Implants (UNS S31673)
than basic wear-screening tests, such as pin-on-disk (see
F370Specification for Proximal Femoral Endoprosthesis
Practice F732) or ring-on-disk (see ISO 6474).
(Withdrawn 2005)
1.3 It is the intent of this guide to rank the combination of
F565PracticeforCareandHandlingofOrthopedicImplants
implant designs and materials with regard to material wear-
and Instruments
rates, under simulated physiological conditions. It must be
F603Specification for High-Purity DenseAluminum Oxide
recognized,however,thattherearemanypossiblevariationsin
for Medical Application
the in vivo conditions, a single laboratory simulation with a
F648Specification for Ultra-High-Molecular-Weight Poly-
fixed set of parameters may not be universally representative.
ethylene Powder and Fabricated Form for Surgical Im-
1.4 The reference materials for the comparative evaluation
plants
of candidate materials, new devices, or components, or a
F732Test Method for Wear Testing of Polymeric Materials
combination thereof, shall be the wear rate of extruded or
Used in Total Joint Prostheses
compression-molded, ultra-high molecular weight (UHMW)
F799Specification for Cobalt-28Chromium-6Molybdenum
polyethylene (see Specification F648) bearing against standard
Alloy Forgings for Surgical Implants (UNS R31537,
counter faces [stainless steel (see Specification F138); cobalt-
R31538, R31539)
chromium-molybdenum alloy (see Specification F75); thermo-
G40Terminology Relating to Wear and Erosion
mechanically processed cobalt chrome (see Specification
2.2 ISO Standard:
F799); alumina ceramic (see Specification F603)], having
ISO6474ImplantsforSurgery–CeramicMaterialsBasedon
typical prosthetic quality, surface finish, and geometry similar
Alumina
to those with established clinical history. These reference
materials will be tested under the same wear conditions as the
candidate materials.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
This guide is under the jurisdiction ofASTM Committee F04 on Medical and Standards volume information, refer to the standard’s Document Summary page on
Surgical Materials and Devicesand is the direct responsibility of Subcommittee the ASTM website.
F04.22 on Arthroplasty. The last approved version of this historical standard is referenced on
CurrenteditionapprovedJune1,2008.PublishedJuly2008.Originallyapproved www.astm.org.
in 1996. Last previous edition approved in 2002 as F1714–96 (2002). DOI: Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/F1714-96R08. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1714 − 96 (2008)
3. Significance and Use 4.3.3 Load—Ensure that the test load profile is representa-
tive of that which occurs during the patient’s walking cycle,
3.1 This guide uses a weight-loss method of wear determi-
with peak hip-loads≥2kN (2).The loading apparatus shall be
nation for the polymeric components used with hip joint
free to follow the specimen as wear occurs, so that the applied
prostheses, using serum or demonstrated equivalent fluid for
load is constant to within 63% for the duration of the test.
lubrication, and running under a dynamic load profile repre-
Never allow the applied load to be below that required to keep
sentative of the human hip-joint forces during walking (1,2).
the chambers seated (for example, 50 N) (4).
The basis for this weight-loss method for wear measurement
4.3.4 Motion—Ensure that relative motion between the hip
was originally developed (3) for pin-on-disk wear studies (see
components oscillates and simulates the flexion-extension arc
PracticeF732)andhasbeenextendedtototalhipreplacements
of walking. Addition of internal-external or abduction-
(4,5) femoral-tibial knee prostheses (6), and to femoropatellar
adduction arcs is at the investigator’s discretion. It is recom-
knee prostheses (6,7).
mendedthattheorientationsofthecupandballrelativetoeach
3.2 While wear results in a change in the physical dimen-
other and to the load-axis be maintained by suitable specimen-
sions of the specimen, it is distinct from dimensional changes
holder keying.
due to creep or plastic deformation, in that wear generally
4.3.5 Oscillating Frequency—Oscillatethehipprosthesesat
results in the removal of material in the form of polymeric
a rate of one cycle per second (1 Hz).
debris particles, causing a loss in weight of the specimen.
4.3.6 Cycle Counter—Include a counter with the hip-
3.3 This guide for measuring wear of the polymeric com- simulator to record the total number of wear cycles.
ponent is suitable for various simulator devices. These tech- 4.3.7 Friction—It is recommended that the machine include
niquescanbeusedwithmetal,ceramic,carbon,polymeric,and sensors capable of monitoring the friction forces transmitted
composite counter faces bearing against a polymeric material across the bearing surfaces during the wear test.
(for example, polyethylene, polyacetal, and so forth). This
4.4 Lubricant:
weight-loss method, therefore, has universal application for
4.4.1 It is recommended that the specimen be lubricated
wear studies of total hip replacements that feature polymeric
withbovinebloodserum;however,anothersuitablelubrication
bearings. This weight-loss method has not been validated for
medium may be used if validated.
high-density material bearing systems, such as metal-metal,
4.4.2 If serum is used, use filtered-sterilized serum rather
carbon-carbon, or ceramic-ceramic. Progressive wear of such
than pooled serum since the former is less likely to contain
rigidbearingcombinationsgenerallyhasbeenmonitoredusing
hemolyzed blood material, which has been shown to adversely
a linear, variable-displacement transducers or by other profi-
affect the lubricating properties of the serum (3). Diluted
lometric techniques.
solutions of serum have also been used for this purpose (8).
Filtration may remove hard, abrasive, particulate contaminants
4. Apparatus and Materials
that might otherwise affect the wear properties of the speci-
4.1 Hip Prosthesis Components—The hip-joint prosthesis
mens being tested.
comprises a ball-and-socket configuration in which materials
4.4.3 Maintain the volume and concentration of the lubri-
such as polymers, composites, metal alloys, ceramics, and
cant nearly constant throughout the test. This may be accom-
carbon have been used in various combinations and designs.
plished by sealing the chambers so that water does not
4.2 Component Configurations—The diameter of the pros- evaporate,orperiodicallyorcontinuouslyreplacingevaporated
thetic ball may vary from 22 to 54 mm or larger. The design water with distilled water.
may include ball-socket, trunnion, bipolar, or other configura- 4.4.4 To retard bacterial degradation, freeze and store the
tions. serumuntilneededforthetest.Inaddition,ensurethatthefluid
medium in the test contains 0.2% sodium azide (or other
4.3 Hip Simulator:
suitable antibiotic) to minimize bacterial degradation. Other
4.3.1 Test Chambers—In the case of a multi-specimen
lubricantsshouldbeevaluatedtodetermineappropriatestorage
machine, contain the components in individual, isolated cham-
conditions.
bers to prevent contamination of one set of components with
4.4.5 It is recommended that ethylene-diaminetetraacetic
debris from another test. Ensure that the chamber is made
acid (EDTA) be added to the serum at a concentration of 20
entirely of noncorrosive materials, such as acrylic plastic or
mM to bind calcium in solution and minimize precipitation of
stainless steel, and is easily removable from the machine for
calcium phosphate onto the bearing surfaces. The latter event
thorough cleaning between tests. Design the wear chambers
has been shown to strongly affect the friction and wear
suchthatthetestbearingsurfacesareimmersedinthelubricant
properties, particularly of polyethylene/ceramic combinations.
throughout the test (3,7).
The addition of EDTA to other lubricant mediums should be
4.3.2 Component Clamping Fixtures—Since wear is to be
evaluated.
determined from the weight-loss of the components, the
4.4.6 Alubricant other than bovine serum may be used if it
method for mounting the components in the test chamber
can be shown that its lubricating properties and, therefore,
should not compromise the accuracy of assessment of the
material wear properties are reasonably physiological (8).In
weight-loss due to wear.
such a case, specify the lubricant in the test report.
4.5 Hold the bulk temperature of the lubricant at 37 6 3°C
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard. or as specified, if different.
F1714 − 96 (2008)
5. Specimen Preparation polymers such as polyethylene may show a net increase in
weight during the initial wear intervals, due to fluid sorption
5.1 The governing rule for preparation of component coun-
(3,4). The error due to fluid sorption can be reduced through
ter faces is that the fabrication process parallels that used or
presoakingandtheuseofcontrolsoakspecimens.Thenumber
intendedforuseintheproductionofactualprostheses,inorder
ofspecimensrequiredandthelengthofpresoakingdependson
to produce a specimen with comparable bulk material proper-
thevariabilityandmagnitudeoffluidsorptionencountered (4).
ties and surface characteristics (see Practice F86).
5.3.2 After fabrication and characterization, clean and dry
5.2 Polymers and Composites:
the wear components and three soak-control components of
5.2.1 Obtain a fabrication history for each polymeric or each test material in accordance with Annex A4, and then
composite component, including information such as grade,
weigh by precisely controlled and repeatable methods. Place
batch number, and processing variables, including method of thewearcomponentsandsoakcontrolsinacontainerofserum
forming (extruding, molding, and so forth), temperature,
for a specified time interval. Then, remove, clean, dry, and
pressure, and forming time used, and any post-forming reweigh the components, and calculate the weight-loss (see
treatments, including sterilization.
Annex A4). Repeat the specimens until a steady rate of
5.2.2 Pretest characterization may include measurement of fluid-sorption has been established. The number of weighings
bulk material properties, such as molecular-weight range and will depend on the amount of fluid sorption exhibited by the
distribution, percent crystallinity, density, or other.The surface specimens.
finish of specimens may be characterized by profilometry, 5.3.3 Ingeneral,theweightofthecomponentswillstabilize
photomicrography, replication by various plastics, or other at an asymptotic value in a reasonable time period. With
techniques. UHMW polyethylene, a presoak period of 30 days has been
found adequate (4,7). In any case, use the weight-gain of the
5.2.3 Sterilization—Sterilize the components in a manner
soak controls to correct for ongoing fluid sorption by the wear
typical of that in clinical use for such devices, including total
components during the wear test.
dose and dose rate, as these may affect the wear properties of
the materials. Report these processing parameters with the
5.4 Counterfaces of Metal Alloys, Ceramic, or Other Mate-
aging time prior to each test when known. Sterilization of all
rials:
testandcontrolcomponentswithinaspecifictestgroupshould
5.4.1 Characterization—Include with the pretest character-
be done simultaneously (in a single container), when possible,
ization of metal, ceramic, or other materials, recording of
to minimize variation among the specimens. This wear-
fabrication variables, such as composition, forming method
simulationproceduremakesnoattempttomaintainthesterility
(forging, casting, and so forth) and any postforming
of specimens during the wear test.
processing, such as annealing. Obtain data on material prop-
5.2.4 Cleaning of Polymer Prostheses—Prior to wear
erties relevant to wear (for example, grain structure, hardness,
testing,carefulcleaningofthepolymerspecimensisimportant
and percentage of contaminants).
to remove any contaminants that would not normally be
5.4.2 Surface Finish—In tests that are intended to evaluate
present on the actual prosthesis. During the wear run, the
an alternate counter face material bearing against the standard
components must be re-cleaned and dried before each weigh-
UHMWPE, ensure that the counter face finish is appropriate
ing to remove any extraneous material that might affect the
for components intended for clinical use. In tests of alternate
accuracy of the weighing.Asuggested procedure for cleaning
materialswhereareferencemetalorceramicisused,polishthe
and drying of polymeric components is given in Annex A4.
counter face to the prosthesis quality.
With some combinations of materials, wear may result in the
5.4.3 Clean
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.