ASTM F1714-96
(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
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 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: F 1714 – 96
Standard Guide for
Gravimetric Wear Assessment of Prosthetic Hip-Designs in
Simulator Devices
This standard is issued under the fixed designation F 1714; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope F 75 Specification for Cast Cobalt-Chromium-Molybdenum
Alloy for Surgical Implant Applications
1.1 This guide describes a laboratory method using a
F 86 Practice for Surface Preparation and Marking of Me-
weight-loss technique for evaluating the wear properties of
tallic Surgical Implants
materials or devices, or both, which are being considered for
F 136 Specification for Titanium 6A1-4V ELI Alloy for
use as bearing surfaces of human-hip-joint replacement pros-
Surgical Implant Applications
theses. The hip prostheses are evaluated in a device intended to
F 138 Specification for Stainless Steel Bar and Wire for
simulate the tribological conditions encountered in the human
Surgical Implants (Special Quality)
hip joint, for example, use of a fluid such as bovine serum, or
F 370 Specification for Proximal Femoral Prosthesis
equivalent pseudosynovial fluid shown to simulate similar
F 565 Practice for Care and Handling of Orthopedic Im-
wear mechanisms and debris generation as found in vivo, and
plants and Instruments
test frequencies of 1 Hz or less.
F 603 Specification for High-Purity Dense Aluminum Ox-
1.2 Since the hip simulator method permits the use of actual
ide for Surgical Implant Application
implant designs, materials, and physiological load/motion
F 648 Specification for Ultra-High-Molecular-Weight Poly-
combinations, it can represent a more physiological simulation
ethylene Powder and Fabricated Form for Surgical Im-
than basic wear-screening tests, such as pin-on-disk (see
plants
Practice F 732) or ring-on-disk (see ISO-6474).
F 732 Practice for Pin-on-Flat Evaluation of Friction and
1.3 It is the intent of this guide to rank the combination of
Wear Properties of Polymeric Materials for Use in Total
implant designs and materials with regard to material wear-
Joint Prostheses
rates, under simulated physiological conditions. It must be
F 799 Specification for Thermomechanically Processed
recognized, however, that there are many possible variations in
Cobalt-Chrome-Molybdenum Alloy for Surgical Implants
the in vivo conditions, a single laboratory simulation with a
G 40 Terminology Relating to Erosion and Wear
fixed set of parameters may not be universally representative.
2.2 ISO Standard:
1.4 The reference materials for the comparative evaluation
ISO 6474 Implants for Surgery–Ceramic Materials Based
of candidate materials, new devices, or components, or a
on Alumina
combination thereof, shall be the wear rate of extruded or
compression-molded, ultra-high molecular weight (UHMW)
3. Significance and Use
polyethylene (see Specification F 648) bearing against standard
3.1 This guide uses a weight-loss method of wear determi-
counter faces [stainless steel (see Specification F 138); cobalt-
nation for the polymeric components used with hip-joint
chromium-molybdenum alloy (see Specification F 75); ther-
prostheses, using serum or demonstrated equivalent fluid for
momechanically processed cobalt chrome (see Specification
lubrication, and running under a dynamic load profile repre-
F 799); alumina ceramic (see Specification F 603)], having
sentative of the human hip-joint forces during walking (1,2).
typical prosthetic quality, surface finish, and geometry similar
The basis for this weight-loss method for wear measurement
to those with established clinical history. These reference
was originally developed (3) for pin-on-disk wear studies (see
materials will be tested under the same wear conditions as the
Practice F 732) and has been extended to total hip replace-
candidate materials.
ments (4,5) and to femoral-tibial knee prostheses (6), and to
2. Referenced Documents femoropatellar knee prostheses (6,7).
2.1 ASTM Standards:
D 883 Terminology Relating to Plastics
Annual Book of ASTM Standards, Vol 13.01.
This guide is under the jurisdiction of ASTM Committee F-4 on Medical and Annual Book of ASTM Standards, Vol 03.02.
Surgical Materials and Devicesand is the direct responsibility of Subcommittee Available from American National Standards Institute, 11 W. 42nd St., 13th
F04.22on Arthroplasty. Floor, New York, NY 10036.
Current edition approved Sept. 10, 1996. Published October 1996. The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 08.01. this standard.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
F 1714
3.2 While wear results in a change in the physical dimen- 4.3.6 Cycle Counter—Include a counter with the hip-
sions of the specimen, it is distinct from dimensional changes simulator to record the total number of wear cycles.
due to creep or plastic deformation, in that wear generally 4.3.7 Friction—It is recommended that the machine include
results in the removal of material in the form of polymeric sensors capable of monitoring the friction forces transmitted
debris particles, causing a loss in weight of the specimen. across the bearing-surfaces during the wear test.
3.3 This guide for measuring wear of the polymeric com- 4.4 Lubricant:
ponent is suitable for various simulator devices. These tech- 4.4.1 It is recommended that the specimen be lubricated
niques can be used with metal, ceramic, carbon, polymeric, and with bovine blood serum, however, another suitable lubrication
composite counter faces bearing against a polymeric material medium may be used if validated.
(for example, polyethylene, polyacetal, and so forth). This 4.4.2 If serum is used, then use filtered-sterilized serum
weight-loss method, therefore, has universal application for rather than pooled serum since the former is less likely to
wear studies of total-hip replacements that feature polymeric contain hemolyzed blood material, which has been shown to
bearings. This weight-loss method has not been validated for adversely affect the lubricating properties of the serum (3).
high-density material bearing systems, such as metal-metal, Diluted solutions of serum also have been used for this purpose
carbon-carbon, or ceramic-ceramic. Progressive wear of such (8). Filtration may remove hard, abrasive, particulate contami-
rigid bearing combinations generally has been monitored using nants that might otherwise affect the wear properties of the
a linear, variable-displacement transducers or by other profilo- specimens being tested.
metric techniques. 4.4.3 Maintain the volume and concentration of the lubri-
cant nearly constant throughout the test. This may be accom-
4. Apparatus and Materials
plished by sealing the chambers so that water does not
4.1 Hip Prosthesis Components—The hip-joint prosthesis
evaporate, or periodically or continuously replacing evaporated
comprises a ball-and-socket configuration in which materials
water with distilled water.
such as polymers, composites, metal alloys, ceramics, and
4.4.4 To retard bacterial degradation, freeze and store the
carbon have been used in various combinations and designs.
serum until needed for test. In addition, ensure that the fluid
4.2 Component Configurations—The diameter of the pros-
medium in the test contains 0.2 % sodium azide (or other
thetic ball may vary from 22 to 54 mm or larger. The design
suitable antibiotic) to minimize bacterial degradation. Other
may include ball-socket, trunnion, bipolar, or other configura-
lubricants should be evaluated to determine appropriate storage
tions.
conditions.
4.3 Hip Simulator:
4.4.5 It is recommended that ethylene-diaminetetraacetic
4.3.1 Test Chambers—In the case of a multi-specimen
acid (EDTA) be added to the serum at a concentration of 20
machine, contain the components in individual, isolated cham-
mM to bind calcium in solution and minimize precipitation of
bers to prevent contamination of one set of components with
calcium phosphate onto the bearing surfaces. The latter event
debris from another test. Ensure that the chamber is made
has been shown to strongly affect the friction and wear
entirely of noncorrosive materials, such as acrylic plastic or
properties, particularly of polyethylene/ceramic combinations.
stainless steel, and is easily removable from the machine for
The addition of EDTA to other lubricant mediums should be
thorough cleaning between tests. Design the wear chambers
evaluated.
such that the test bearing surfaces are immersed in the lubricant
4.4.6 A lubricant other than bovine serum may be used
throughout the test (3,7).
when it can be shown that its lubricating properties and,
4.3.2 Component Clamping Fixtures—Since wear is to be
therefore, material wear properties are reasonably physiologi-
determined from the weight loss of the components, the
cal (8). In such a case, specify the lubricant in the test report.
method for mounting the components in the test chamber
4.5 Hold the bulk temperature of the lubricant at 376 3°C
should not compromise the accuracy of assessment of the
or specified, if different.
weight-loss due to wear.
5. Specimen Preparation
4.3.3 Load—Ensure that the test load profile is representa-
tive of that which occurs during the patients walking cycle, 5.1 The governing rule for preparation of component
with peak hip-loads $2kN (2). The loading apparatus must be counter faces is that the fabrication process parallels that used
free to follow the specimen as wear occurs, such that the or intended for use in the production of actual prostheses, in
applied load is constant to within 63 % for the duration of the order to produce a specimen with comparable bulk material
test. Never allow the applied load to be below that required to properties and surface characteristics (see Practice F 86).
keep the chambers seated (for example, 50 N) (4). 5.2 Polymers and Composites:
4.3.4 Motion—Ensure that relative motion between the hip 5.2.1 Obtain a fabrication history for each polymeric or
components oscillates and simulates the flexion-extension arc composite component, including information such as grade,
of walking. Addition of internal-external or abduction- batch number, and processing variables, including method of
adduction arcs is at the investigator’s discretion. It is recom- forming (extruding, molding, and so forth), temperature, pres-
mended that the orientations of the cup and ball relative to each sure, and forming time used, and any post-forming treatments,
other and to the load-axis be maintained by suitable specimen- including sterilization.
holder keying. 5.2.2 Pretest characterization may include measurement of
4.3.5 Oscillating Frequency—Oscillate the hip prostheses at bulk material properties, such as molecular-weight range and
a rate of one cycle per second (1 Hz). distribution, percent crystallinity, density, or other. The surface
F 1714
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
soak controls to correct for ongoing fluid sorption by the wear
5.2.3 Sterilization—Sterilize the components in a manner
components during the wear test.
typical of that in clinical use for such devices, including total
5.4 Counterfaces of Metal Alloys, Ceramic, or Other Mate-
dose and dose rate, as these may affect the wear properties of
rials:
the materials. Report these processing parameters with the
5.4.1 Characterization—Include with the pretest character-
aging time prior to each test when known. Sterilization of all
ization of metal, ceramic, or other materials, recording of
test and control components within a specific test group should
fabrication variables, such as composition, forming method
be done simultaneously (in a single container), when possible,
(forging, casting, and so forth) and any postforming process-
to minimize variation among the specimens. This wear-
ing, such as annealing. Obtain data on material properties
simulation procedure makes no attempt to maintain the sterility
relevant to wear (for example, grain structure, hardness, and
of specimens during the wear test.
percentage of contaminants).
5.2.4 Cleaning of Polymer Prostheses—Prior to wear test-
5.4.2 Surface Finish—In tests that are intended to evaluate
ing, careful cleaning of the polymer specimens is important to
an alternate counter face material bearing against the standard
remove any contaminants that would not normally be present
UHMWPE, ensure that the counter face finish is appropriate
on the actual prosthesis. During the wear run, the components
for components intended for clinical use. In tests of alternate
must be re-cleaned and dried before each weighing to remove
materials where a reference metal or ceramic is used, polish the
any extraneous material that might affect the accuracy of the
counter face to the prosthesis quality.
weighing. A suggested procedure for cleaning and drying of
5.4.3 Clean, degrease, and passivate components of refer-
polymeric components is given in Annex A4. With some
enced prosthetic metals or ceramics in accordance with Prac-
combinations of materials, wear may result in the transfer of
tice F 86. This practice may require modification for compo-
particulate debris which may then become reimbedded or
nents of other materials. Ensure that cleaning of components
otherwise attached to polymeric, metal, or composite surfaces.
produces a surface free of any particles, oils, greases, or other
Such an occurrence will render the weight-loss assessment of
contaminants that might influence the wear process.
wear less reliable.
5.2.5 Weighing of Polymeric Components—Weigh the poly-
6. Measurement Procedure
meric components on an analytical balance having an accuracy
6.1 At the completion of the presoak period, the wear
on the order of6 10 μg. This degree of sensitivity is necessary
components and soak controls should be removed from the
to detect the slight loss in weight of polymers, such as UHMW
soak bath, cleaned, dried, and weighed by precisely controlled
polyethylene, which may wear 30 mg or less per million cycles
and repeatable methods. Record these weights as the initial
(3,5). Always weight specimens in the clean, dry condition (see
weights of the specimens for p
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