ASTM F1714-96(2002)
(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).6 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) and to 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 terminological conditions encountered in the human hip joint, for example, use of a fluid such as bovine serum, or equivalent pseudosynovial fluid shown to simulate 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 pinion-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.
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Designation:F1714–96 (Reapproved 2002)
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 (e) 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 D883 Terminology Relating to Plastics
materials or devices, or both, which are being considered for F75 SpecificationforCastCobalt-Chromium-Molybdenum
use as bearing surfaces of human-hip-joint replacement pros- Alloy for Surgical Implant Applications
theses.Thehipprosthesesareevaluatedinadeviceintendedto F86 Practice for Surface Preparation and Marking of Me-
simulate the tribological conditions encountered in the human tallic Surgical Implants
hip joint, for example, use of a fluid such as bovine serum, or F136 Specification for Titanium 6A1-4V ELI Alloy for
equivalent pseudosynovial fluid shown to simulate similar Surgical Implant Applications
wear mechanisms and debris generation as found in vivo, and F138 Specification for Stainless Steel Bar and Wire for
test frequencies of 1 Hz or less. Surgical Implants (Special Quality)
1.2 Sincethehipsimulatormethodpermitstheuseofactual F370 Specification for Proximal Femoral Prosthesis
implant designs, materials, and physiological load/motion F565 Practice for Care and Handling of Orthopedic Im-
combinations, it can represent a more physiological simulation plants and Instruments
than basic wear-screening tests, such as pin-on-disk (see F603 Specification for High-Purity Dense Aluminum Ox-
Practice F732) or ring-on-disk (see ISO 6474). ide for Surgical Implant Application
1.3 It is the intent of this guide to rank the combination of F648 Specification for Ultra-High-Molecular-Weight Poly-
implant designs and materials with regard to material wear- ethylene Powder and Fabricated Form for Surgical Im-
rates, under simulated physiological conditions. It must be plants
recognized,however,thattherearemanypossiblevariationsin F732 Practice for Pin-on-Flat Evaluation of Friction and
the in vivo conditions, a single laboratory simulation with a Wear Properties of Polymeric Materials for Use in Total
fixed set of parameters may not be universally representative. Joint Prostheses
1.4 The reference materials for the comparative evaluation F 799 Specification for Thermomechanically Processed
of candidate materials, new devices, or components, or a Cobalt-Chrome-MolybdenumAlloy for Surgical Implants
combination thereof, shall be the wear rate of extruded or G40 Terminology Relating to Erosion and Wear
compression-molded, ultra-high molecular weight (UHMW) 2.2 ISO Standard:
polyethylene(seeSpecificationF648)bearingagainststandard ISO 6474 Implants for Surgery–Ceramic Materials Based
counter faces [stainless steel (see Specification F138); cobalt- on Alumina
chromium-molybdenum alloy (see Specification F75); ther-
3. Significance and Use
momechanically processed cobalt chrome (see Specification
F799); alumina ceramic (see Specification F603)], having 3.1 This guide uses a weight-loss method of wear determi-
nation for the polymeric components used with hip-joint
typical prosthetic quality, surface finish, and geometry similar
to those with established clinical history. These reference prostheses, using serum or demonstrated equivalent fluid for
materials will be tested under the same wear conditions as the
candidate materials.
Annual Book of ASTM Standards, Vol 08.01.
1 3
This guide is under the jurisdiction ofASTM Committee F04 on Medical and Annual Book of ASTM Standards, Vol 13.01.
Surgical Materials and Devicesand is the direct responsibility of Subcommittee Annual Book of ASTM Standards, Vol 03.02.
F04.22on Arthroplasty. Available from American National Standards Institute, 25 W. 43rd St., 4th
Current edition approved Sept. 10, 1996. Published October 1996. Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F1714
lubrication, and running under a dynamic load profile repre- test. Never allow the applied load to be below that required to
sentative of the human hip-joint forces during walking (1,2). keep 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
Practice F732) and has been extended to total hip replace-
of walking. Addition of internal-external or abduction-
ments (4,5) and to femoral-tibial knee prostheses (6), and to adduction arcs is at the investigator’s discretion. It is recom-
femoropatellar 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—Itisrecommendedthatthemachineinclude
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, then use filtered-sterilized serum
carbon-carbon, or ceramic-ceramic. Progressive wear of such
rather than pooled serum since the former is less likely to
rigidbearingcombinationsgenerallyhasbeenmonitoredusing
contain hemolyzed blood material, which has been shown to
a linear, variable-displacement transducers or by other profilo-
adversely affect the lubricating properties of the serum (3).
metric techniques.
Dilutedsolutionsofserumalsohavebeenusedforthispurpose
(8). Filtration may remove hard, abrasive, particulate contami-
4. Apparatus and Materials
nants that might otherwise affect the wear properties of the
4.1 Hip Prosthesis Components—The hip-joint prosthesis
specimens 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.
serum until needed for test. In addition, ensure that the fluid
4.3 Hip Simulator:
medium in the test contains 0.2% sodium azide (or other
4.3.1 Test Chambers—In the case of a multi-specimen
suitable antibiotic) to minimize bacterial degradation. Other
machine, contain the components in individual, isolated cham-
lubricantsshouldbeevaluatedtodetermineappropriatestorage
bers to prevent contamination of one set of components with
conditions.
debris from another test. Ensure that the chamber is made
4.4.5 It is recommended that ethylene-diaminetetraacetic
entirely of noncorrosive materials, such as acrylic plastic or
acid (EDTA) be added to the serum at a concentration of 20
stainless steel, and is easily removable from the machine for
mM to bind calcium in solution and minimize precipitation of
thorough cleaning between tests. Design the wear chambers
calcium phosphate onto the bearing surfaces. The latter event
suchthatthetestbearingsurfacesareimmersedinthelubricant
has been shown to strongly affect the friction and wear
throughout the test (3,7).
properties, particularly of polyethylene/ceramic combinations.
4.3.2 Component Clamping Fixtures—Since wear is to be
The addition of EDTA to other lubricant mediums should be
determined from the weight loss of the components, the
evaluated.
method for mounting the components in the test chamber
4.4.6 A lubricant other than bovine serum may be used
should not compromise the accuracy of assessment of the
when it can be shown that its lubricating properties and,
weight-loss due to wear.
therefore, material wear properties are reasonably physiologi-
4.3.3 Load—Ensure that the test load profile is representa-
cal (8). In such a case, specify the lubricant in the test report.
tive of that which occurs during the patients walking cycle,
4.5 Hold the bulk temperature of the lubricant at 37 6 3°C
withpeakhip-loads$2kN (2).Theloadingapparatusmustbe
or specified, if different.
free to follow the specimen as wear occurs, such that the
applied load is constant to within 63% for the duration of the
5. Specimen Preparation
5.1 The governing rule for preparation of component
counter faces is that the fabrication process parallels that used
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard. or intended for use in the production of actual prostheses, in
F1714
order to produce a specimen with comparable bulk material ofspecimensrequiredandthelengthofpresoakingdependson
properties and surface characteristics (see Practice F86). thevariabilityandmagnitudeoffluidsorptionencountered (4).
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, pres-
for a specified time interval. Then, remove, clean, dry, and
sure, and forming time used, and any post-forming treatments,
reweigh the components, and calculate the weight (seeAnnex
including sterilization.
A4). Repeat the specimens until a steady rate of fluid-sorption
5.2.2 Pretest characterization may include measurement of
hasbeenestablished.Thenumberofweighingswilldependon
bulk material properties, such as molecular-weight range and
the amount of fluid sorption exhibited by the 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 process-
simulationproceduremakesnoattempttomaintainthesterility
ing, such as annealing. Obtain data on material properties
of specimens during the wear test.
relevant to wear (for example, grain structure, hardness, and
5.2.4 Cleaning of Polymer Prostheses—Prior to wear test-
percentage of contaminants).
ing, careful cleaning of the polymer specimens is important to
5.4.2 Surface Finish—In tests that are intended to evaluate
remove any contaminants that would not normally be present
an alternate counter face material bearing against the standard
on the actual prosthesis. During the wear run, the components
UHMWPE, ensure that the counter face finish is appropriate
must be re-cleaned and dried before each weighing to remove
for components intended for clinical use. In tests of alternate
any extraneous material that might affect the accuracy of the
materialswhereareferencemetalorceramicisused,polishthe
weighing. A suggested procedure for cleaning and drying of
counter face to the prosthesis quality.
polymeric components is given in Annex A4. With some
5.4.3 Clean, degrease, and passivate components of refer-
combinations of materials, wear may result in the transfer of
enced prosthetic metals or ceramics in accordance with Prac-
particulate debris which may then become reimbedded or
tice F86. This practice may require modification for compo-
otherwise attached to polymeric, metal, or composite surfaces.
nents of other materials. Ensure that cleaning of components
Such an occurrence will render the weight-loss assessment of
produces a surface free of any particles, oils, greases, or other
wear less reliable.
contaminants that might influence the wear process.
5.2.5 Weighing of Polymeric Components—Weighthepoly-
mericcomponentsonan
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