ASTM F1714-96(2013)
(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
3.1 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).5 The basis for this weight-loss method for wear measurement was originally developed (3) for pin-on-disk wear studies (see Practice F732) and has been extended to total hip replacements (4,5) femoral-tibial knee prostheses (6), and to femoropatellar knee prostheses (6,7).
3.2 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.
3.3 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 F732) 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 F648) bearing against standard counter faces [stainless steel (see Specification F138); cobalt-chromium-molybdenum alloy (see Specification F75); thermomechanically processed cobalt chrome (see Specification F799); alumina ceramic (see Specification F603)], 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.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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Designation: F1714 − 96 (Reapproved 2013)
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 to those with established clinical history. These reference
materials will be tested under the same wear conditions as the
1.1 This guide describes a laboratory method using a
candidate materials.
weight-loss technique for evaluating the wear properties of
materials or devices, or both, which are being considered for 1.5 The values stated in SI units are to be regarded as
use as bearing surfaces of human-hip-joint replacement pros- standard. No other units of measurement are included in this
theses.Thehipprosthesesareevaluatedinadeviceintendedto standard.
simulate the tribological conditions encountered in the human
2. Referenced Documents
hip joint, for example, use of a fluid such as bovine serum, or
equivalent pseudosynovial fluid shown to simulate similar 2.1 ASTM Standards:
wear mechanisms and debris generation as found in vivo, and
D883Terminology Relating to Plastics
test frequencies of 1 Hz or less. F75Specification for Cobalt-28 Chromium-6 Molybdenum
Alloy Castings and Casting Alloy for Surgical Implants
1.2 Sincethehipsimulatormethodpermitstheuseofactual
(UNS R30075)
implant designs, materials, and physiological load/motion
F86Practice for Surface Preparation and Marking of Metal-
combinations, it can represent a more physiological simulation
lic Surgical Implants
than basic wear-screening tests, such as pin-on-disk (see
F136 Specification for Wrought Titanium-6Aluminum-
Practice F732) or ring-on-disk (see ISO 6474).
4VanadiumELI(ExtraLowInterstitial)AlloyforSurgical
1.3 It is the intent of this guide to rank the combination of
Implant Applications (UNS R56401)
implant designs and materials with regard to material wear-
F138 Specification for Wrought 18Chromium-14Nickel-
rates, under simulated physiological conditions. It must be
2.5MolybdenumStainlessSteelBarandWireforSurgical
recognized,however,thattherearemanypossiblevariationsin
Implants (UNS S31673)
the in vivo conditions, a single laboratory simulation with a
F370Specification for Proximal Femoral Endoprosthesis
fixed set of parameters may not be universally representative. 3
(Withdrawn 2005)
1.4 The reference materials for the comparative evaluation F565PracticeforCareandHandlingofOrthopedicImplants
of candidate materials, new devices, or components, or a and Instruments
combination thereof, shall be the wear rate of extruded or F603Specification for High-Purity DenseAluminum Oxide
compression-molded, ultra-high molecular weight (UHMW) for Medical Application
polyethylene (see Specification F648) bearing against standard F648Specification for Ultra-High-Molecular-Weight Poly-
counter faces [stainless steel (see Specification F138); cobalt- ethylene Powder and Fabricated Form for Surgical Im-
chromium-molybdenum alloy (see Specification F75); thermo- plants
mechanically processed cobalt chrome (see Specification F732Test Method for Wear Testing of Polymeric Materials
F799); alumina ceramic (see Specification F603)], having Used in Total Joint Prostheses
typical prosthetic quality, surface finish, and geometry similar F799Specification for Cobalt-28Chromium-6Molybdenum
1 2
This guide is under the jurisdiction ofASTM Committee F04 on Medical and For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Surgical Materials and Devicesand is the direct responsibility of Subcommittee contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
F04.22 on Arthroplasty. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved March 15, 2013. Published April 2013. Originally the ASTM website.
approved in 1996. Last previous edition approved in 2008 as F1714–96 (2008). The last approved version of this historical standard is referenced on
DOI: 10.1520/F1714-96R13. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1714 − 96 (2013)
Alloy Forgings for Surgical Implants (UNS R31537, stainless steel, and is easily removable from the machine for
R31538, R31539) thorough cleaning between tests. Design the wear chambers
G40Terminology Relating to Wear and Erosion suchthatthetestbearingsurfacesareimmersedinthelubricant
throughout the test (3,7).
2.2 ISO Standard:
ISO6474ImplantsforSurgery–CeramicMaterialsBasedon 4.3.2 Component Clamping Fixtures—Since wear is to be
determined from the weight-loss of the components, the
Alumina
method for mounting the components in the test chamber
3. Significance and Use
should not compromise the accuracy of assessment of the
weight-loss due to wear.
3.1 This guide uses a weight-loss method of wear determi-
4.3.3 Load—Ensure that the test load profile is representa-
nation for the polymeric components used with hip joint
tive of that which occurs during the patient’s walking cycle,
prostheses, using serum or demonstrated equivalent fluid for
with peak hip-loads ≥2kN (2). The loading apparatus shall be
lubrication, and running under a dynamic load profile repre-
free to follow the specimen as wear occurs, so that the applied
sentative of the human hip-joint forces during walking (1,2).
load is constant to within 63% for the duration of the test.
The basis for this weight-loss method for wear measurement
Never allow the applied load to be below that required to keep
was originally developed (3) for pin-on-disk wear studies (see
the chambers seated (for example, 50 N) (4).
PracticeF732)andhasbeenextendedtototalhipreplacements
4.3.4 Motion—Ensure that relative motion between the hip
(4,5) femoral-tibial knee prostheses (6), and to femoropatellar
components oscillates and simulates the flexion-extension arc
knee prostheses (6,7).
of walking. Addition of internal-external or abduction-
3.2 While wear results in a change in the physical dimen-
adduction arcs is at the investigator’s discretion. It is recom-
sions of the specimen, it is distinct from dimensional changes
mendedthattheorientationsofthecupandballrelativetoeach
due to creep or plastic deformation, in that wear generally
other and to the load-axis be maintained by suitable specimen-
results in the removal of material in the form of polymeric
holder keying.
debris particles, causing a loss in weight of the specimen.
4.3.5 Oscillating Frequency—Oscillatethehipprosthesesat
3.3 This guide for measuring wear of the polymeric com-
a rate of one cycle per second (1 Hz).
ponent is suitable for various simulator devices. These tech-
4.3.6 Cycle Counter—Include a counter with the hip-
niquescanbeusedwithmetal,ceramic,carbon,polymeric,and
simulator to record the total number of wear cycles.
composite counter faces bearing against a polymeric material
4.3.7 Friction—It is recommended that the machine include
(for example, polyethylene, polyacetal, and so forth). This
sensors capable of monitoring the friction forces transmitted
weight-loss method, therefore, has universal application for
across the bearing surfaces during the wear test.
wear studies of total hip replacements that feature polymeric
4.4 Lubricant:
bearings. This weight-loss method has not been validated for
4.4.1 It is recommended that the specimen be lubricated
high-density material bearing systems, such as metal-metal,
withbovinebloodserum;however,anothersuitablelubrication
carbon-carbon, or ceramic-ceramic. Progressive wear of such
medium may be used if validated.
rigidbearingcombinationsgenerallyhasbeenmonitoredusing
4.4.2 If serum is used, use filtered-sterilized serum rather
a linear, variable-displacement transducers or by other profi-
than pooled serum since the former is less likely to contain
lometric techniques.
hemolyzed blood material, which has been shown to adversely
affect the lubricating properties of the serum (3). Diluted
4. Apparatus and Materials
solutions of serum have also been used for this purpose (8).
4.1 Hip Prosthesis Components—The hip-joint prosthesis
Filtration may remove hard, abrasive, particulate contaminants
comprises a ball-and-socket configuration in which materials
that might otherwise affect the wear properties of the speci-
such as polymers, composites, metal alloys, ceramics, and
mens being tested.
carbon have been used in various combinations and designs.
4.4.3 Maintain the volume and concentration of the lubri-
4.2 Component Configurations—The diameter of the pros-
cant nearly constant throughout the test. This may be accom-
thetic ball may vary from 22 to 54 mm or larger. The design
plished by sealing the chambers so that water does not
may include ball-socket, trunnion, bipolar, or other configura-
evaporate,orperiodicallyorcontinuouslyreplacingevaporated
tions.
water with distilled water.
4.3 Hip Simulator: 4.4.4 To retard bacterial degradation, freeze and store the
4.3.1 Test Chambers—In the case of a multi-specimen serumuntilneededforthetest.Inaddition,ensurethatthefluid
machine, contain the components in individual, isolated cham- medium in the test contains 0.2% sodium azide (or other
bers to prevent contamination of one set of components with suitable antibiotic) to minimize bacterial degradation. Other
debris from another test. Ensure that the chamber is made lubricantsshouldbeevaluatedtodetermineappropriatestorage
entirely of noncorrosive materials, such as acrylic plastic or conditions.
4.4.5 It is recommended that ethylene-diaminetetraacetic
acid (EDTA) be added to the serum at a concentration of 20
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
mM to bind calcium in solution and minimize precipitation of
4th Floor, New York, NY 10036, http://www.ansi.org.
calcium phosphate onto the bearing surfaces. The latter event
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard. has been shown to strongly affect the friction and wear
F1714 − 96 (2013)
properties, particularly of polyethylene/ceramic combinations. AnnexA1). Keep the components in a dust-free container and
The addition of EDTA to other lubricant mediums should be handle with clean tools to prevent contamination that might
evaluated. affect the weight measurement. Weigh each wear and control
4.4.6 Alubricant other than bovine serum may be used if it component three times in rotation to detect random errors in
can be shown that its lubricating properties and, therefore, the weighing process.
material wear properties are reasonably physiological (8).In
5.3 Soaking of Polymeric and Composite Prostheses:
such a case, specify the lubricant in the test report.
5.3.1 Polymeric and composite components should be pre-
4.5 Hold the bulk temperature of the lubricant at 37 6 3°C soaked in the lubricant to minimize fluid sorption during the
or as specified, if different. wear run. Without presoaking, components of very low-wear
polymers such as polyethylene may show a net increase in
5. Specimen Preparation
weight during the initial wear intervals, due to fluid sorption
(3,4). The error due to fluid sorption can be reduced through
5.1 The governing rule for preparation of component coun-
presoakingandtheuseofcontrolsoakspecimens.Thenumber
ter faces is that the fabrication process parallels that used or
ofspecimensrequiredandthelengthofpresoakingdependson
intendedforuseintheproductionofactualprostheses,inorder
thevariabilityandmagnitudeoffluidsorptionencountered (4).
to produce a specimen with comparable bulk material proper-
5.3.2 After fabrication and characterization, clean and dry
ties and surface characteristics (see Practice F86).
the wear components and three soak-control components of
5.2 Polymers and Composites:
each test material in accordance with Annex A4, and then
5.2.1 Obtain a fabrication history for each polymeric or
weigh by precisely controlled and repeatable methods. Place
composite component, including information such as grade,
thewearcomponentsandsoakcontrolsinacontainerofserum
batch number, and processing variables, including method of
for a specified time interval. Then, remove, clean, dry, and
forming (extruding, molding, and so forth), temperature,
reweigh the components, and calculate the weight-loss (see
pressure, and forming time used, and any post-forming
Annex A4). Repeat the specimens until a steady rate of
treatments, including sterilization.
fluid-sorption has been established. The number of weighings
5.2.2 Pretest characterization may include measurement of
will depend on the amount of fluid sorption exhibited by the
bulk material properties, such as molecular-weight range and
specimens.
distribution, percent crystallinity, density, or other.The surface
5.3.3 Ingeneral,theweightofthecomponentswillstabilize
finish of specimens may be characterized by profilometry,
at an asymptotic value in a reasonable time period. With
photomicrography, replication by various plastics, or other
UHMW polyethylene, a presoak period of 30 days has been
techniques.
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
5.4 Counterfaces of Metal Alloys, Ceramic, or Other Mate-
the materials. Report these processing parameters with the
rials:
aging time prior to each test when known. Sterilization of all
5.4.1 Characterization—Include with the pretest character-
testandcontrolcomponentswithinaspecifictestgroupshould
ization of metal, ceramic, or other materials, recording of
be done simultaneously (in a single container), when possible,
fabrication variables, such as composition, forming method
to minimize variation among the specimens. This wear-
(forging, casting, and so forth) and any postforming
simulationproceduremakesnoattempttomaintainthesterility
processing, such as annealing. Obtain data on material prop-
of specimens during the wear test.
erties relevant to wear (for example, grain structure, hardness,
5.2.4 Cleaning of Polymer Prostheses—Prior to wear
and percentage of contaminants).
testing,carefulcleaningofthepolymerspecimensisimportant
5.4.2 Surface Finish—In tests that are intended to evaluate
to remove any contaminants that would not normally be
an alternate cou
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