ASTM F897-02(2007)
(Test Method)Standard Test Method for Measuring Fretting Corrosion of Osteosynthesis Plates and Screws
Standard Test Method for Measuring Fretting Corrosion of Osteosynthesis Plates and Screws
SIGNIFICANCE AND USE
It is well known from examination of implants after use that plates and screws used for osteosynthesis are subjected to metal loss due to corrosion at the plate-screw interfaces. One of the mechanisms of this corrosive attack is fretting corrosion due to relative motion (micromotion) between the screw heads and plate-hole countersinks.
It is also known that release of corrosion products into the tissues surrounding an implant may have adverse effects on local tissue or have systemic effects. Thus, it is important to minimize the amount of tissue exposure to corrosion products.
Screws and plates are available in different configurations in accordance with Specifications F 543 and F 382. This test method may be used to evaluate the effects of different combinations of screw and plate designs. As new materials and device designs are developed for use in the treatment of fractured bones, it is important to determine the effects these developments have on the amount of metal loss due to fretting corrosion.
This test method provides a standardized screening test for ranking metal plates and screws in terms of resistance to fretting corrosion and for determining the influence of different solutions on fretting corrosion rates.
This test method may also be used to generate corrosion products either for chemical analysis of the products or for testing for biological reactions to corrosion products using animal or cell culture methods.
It is well known that fretting corrosion rates depend on normal load or pressure, frequency, sliding amplitude, materials, surface treatments, and environmental factors. (4) Therefore, when determining the effect of changing one of these parameters (for example, material or environment), all others must be kept constant to facilitate interpretation of the results.
SCOPE
1.1 This test method provides a screening test for determining the amount of metal loss from plates and screws used for osteosynthesis (internal fixation of broken bones) due to fretting corrosion in the contact area between the screw head and the plate hole countersink area. The implants are used in the form they would be used clinically. The machine described generates a relative motion between plates and screws which simulates one type of motion pattern that can occur when these devices are used clinically.
1.2 Since the environmental and stress conditions used in this test method may not be identical to those experienced by bone plates in the human body, this test method may produce fretting corrosion rates that are lower or higher than those experienced in practice. The recommended axial load of 400 N was selected as being in a range where the amount of fretting corrosion is not sensitive to small changes in axial load (1). The combination of the recommended load and angular displacement are such that a measurable amount of fretting corrosion of surgical alloys occurs in a comparatively short period of time (7 to 14 days). (Refs 1-3)
1.3 The device is designed so as to facilitate sterilization of the test specimens and test chambers to permit testing with proteinaceous solutions that would become contaminated with microbial growth in nonsterile conditions.
1.4 The specimens used can be standard osteosynthesis implants or can be materials fabricated into the appropriate shapes.
1.5 This test method may be used for testing the fretting corrosion of metal plates and screws of similar or different alloy compositions, or it may be used for testing the fretting corrosion of metal-nonmetal combinations. This test method may also be used for wear or degradation studies of nonmetallic materials. This test method may be used as a screening test to rank the corrosivities of saline or proteinaceous solutions, or to rank metal-to-metal couples for resistance to fretting corrosion, or to study other material combinations.
1.6 The values stated in SI units are to be regarded as the standard. The va...
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Designation: F897 − 02(Reapproved 2007)
Standard Test Method for
Measuring Fretting Corrosion of Osteosynthesis Plates and
Screws
ThisstandardisissuedunderthefixeddesignationF897;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope tallic materials. This test method may be used as a screening
test to rank the corrosivities of saline or proteinaceous
1.1 This test method provides a screening test for determin-
solutions, or to rank metal-to-metal couples for resistance to
ing the amount of metal loss from plates and screws used for
fretting corrosion, or to study other material combinations.
osteosynthesis (internal fixation of broken bones) due to
fretting corrosion in the contact area between the screw head 1.6 The values stated in SI units are to be regarded as the
and the plate hole countersink area. The implants are used in standard. The values given in parentheses are for information
the form they would be used clinically. The machine described only.
generates a relative motion between plates and screws which
1.7 This standard may involve hazardous materials,
simulates one type of motion pattern that can occur when these
operations, and equipment. This standard does not purport to
devices are used clinically.
address all of the safety concerns associated with its use. It is
the responsibility of whoever uses this standard to consult and
1.2 Since the environmental and stress conditions used in
establish appropriate safety and health practices and deter-
this test method may not be identical to those experienced by
mine the applicability of regulatory limitations prior to use.
bone plates in the human body, this test method may produce
fretting corrosion rates that are lower or higher than those
2. Referenced Documents
experienced in practice.The recommended axial load of 400 N
was selected as being in a range where the amount of fretting
2.1 ASTM Standards:
corrosion is not sensitive to small changes in axial load (1).
D1886 Test Methods for Nickel in Water
The combination of the recommended load and angular dis-
F86 Practice for Surface Preparation and Marking of Metal-
placement are such that a measurable amount of fretting
lic Surgical Implants
corrosion of surgical alloys occurs in a comparatively short
F382 SpecificationandTestMethodforMetallicBonePlates
period of time (7 to 14 days). (Refs 1-3)
F543 Specification and Test Methods for Metallic Medical
Bone Screws
1.3 The device is designed so as to facilitate sterilization of
G1 Practice for Preparing, Cleaning, and Evaluating Corro-
the test specimens and test chambers to permit testing with
sion Test Specimens
proteinaceous solutions that would become contaminated with
microbial growth in nonsterile conditions.
3. Summary of Test Method
1.4 The specimens used can be standard osteosynthesis
3.1 A two-hole plate is attached to two plastic rods with
implants or can be materials fabricated into the appropriate
bone screws, with flexible spacers between the plate and the
shapes.
rods, placed in a glass beaker, and the beaker sealed with a
1.5 This test method may be used for testing the fretting
flexible rubber cover. This assembly is steam sterilized, and
corrosion of metal plates and screws of similar or different
then a sterile solution is injected through the rubber cover into
alloy compositions, or it may be used for testing the fretting
the beaker. This assembly is then mounted in the fretting
corrosion of metal-nonmetal combinations. This test method
apparatus which, when set in motion, produces a rocking
may also be used for wear or degradation studies of nonme-
motion and, therefore, a small cyclic displacement between the
mating surfaces of the plate and screws.The amount of fretting
corrosion is determined at the end of the test by measurement
This test method is under the jurisdiction ofASTM Committee F04 on Medical
and Surgical Materials and Devicesand is the direct responsibility of Subcommittee
F04.15 on Material Test Methods.
Current edition approved Oct. 1, 2007. Published October 2007. Originally
approved in 1984. Last previous edition approved in 2002 as F897 – 02. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/F0897-02R07. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to the list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F897 − 02 (2007)
of the weight loss of the plates and screws and by chemical 4.6 It is well known that fretting corrosion rates depend on
analysis of the solutions. normal load or pressure, frequency, sliding amplitude,
materials, surface treatments, and environmental factors. (4)
4. Significance and Use
Therefore, when determining the effect of changing one of
4.1 It is well known from examination of implants after use these parameters (for example, material or environment), all
that plates and screws used for osteosynthesis are subjected to others must be kept constant to facilitate interpretation of the
metallossduetocorrosionattheplate-screwinterfaces.Oneof
results.
the mechanisms of this corrosive attack is fretting corrosion
due to relative motion (micromotion) between the screw heads
5. Apparatus
and plate-hole countersinks.
5.1 Steam Autoclave, capable of maintaining 121 6 2°C
4.2 It is also known that release of corrosion products into
(250 6 4°F), and equipped with a thermometer, pressure
the tissues surrounding an implant may have adverse effects on
gauge, vent cock, and a rack to hold the test assemblies above
local tissue or have systemic effects. Thus, it is important to
the water level.
minimize the amount of tissue exposure to corrosion products.
5.2 Microbalance, with a 0.01-mg scale.
4.3 Screws and plates are available in different configura-
tions in accordance with Specifications F543 and F382. This
5.3 Fretting Apparatus, as described in 5.3.1-5.3.4 and
test method may be used to evaluate the effects of different
illustrated in Fig. 1.
combinations of screw and plate designs.As new materials and
5.3.1 The fretting apparatus is driven by a slow speed gear
device designs are developed for use in the treatment of
motor connected to a horizontal rotating shaft. Round disks
fractured bones, it is important to determine the effects these
with machined flats (cams) are mounted on the shaft as shown
developments have on the amount of metal loss due to fretting
in Fig. 1. For multiple specimen testing, there may be more
corrosion.
than one cam on the drive shaft.
4.4 This test method provides a standardized screening test
5.3.2 Theflatsonthecamsaremachinedsoastoproduce2°
for ranking metal plates and screws in terms of resistance to
of relative motion between the posts of the test assemblies.
fretting corrosion and for determining the influence of different
solutions on fretting corrosion rates. NOTE 1—A suggested combination of short post length and plunger
displacement is a 5-cm post with a 1.9-mm displacement.
4.5 This test method may also be used to generate corrosion
5.3.3 The shaft rotation rate and the number of machined
products either for chemical analysis of the products or for
flats shall be such that the flats produce one oscillation of the
testing for biological reactions to corrosion products using
animal or cell culture methods. plunger per second.
NOTE 1—Figure shows assembly drawings of one pair of test positions on each side of a cam, and of the relationships between the screws, plate,
spacers, and polyacetal rods.
FIG. 1 Two-Hole Plate Fretting (THPF) Testing System
F897 − 02 (2007)
sterileinaccordancewith8.1.5.Proteinsolutionsmayeitherbe
purchased sterile, or sterilized by filtration. These shall be
reported in accordance with 10.1.
7. Test Specimens
7.1 Plates:
7.1.1 The plates used for these tests may be cut from
commercially available plates for osteosynthesis.
7.1.2 Platesmaybefabricatedfrom3.5-mmorthickermetal
sheet or strip. Holes may be prepared in accordance with
Specification F382. Holes may be round, or slotted, or “self-
compressing” type.
7.2 Screws:
FIG. 2 Assembled Test Chamber with Rubber Seal
7.2.1 Screws used for this test may be commercially avail-
able bone screws. Heads should be spherical, although other
5.3.4 Testassemblyholdinganddrivingframesaremounted
shapes may be used.
symmetrically on each side of the rotating cams. The oscillat-
7.2.2 Screws may be fabricated from rod stock in accor-
ing plunger is springloaded and held in the guide sleeve. The
dance with Specification F543.
hole in the top plate is slotted to permit adjustment of the
7.3 Test specimens may be used in the condition as received
position of the test assemblies.
from the implant manufacturer; custom fabricated specimens
5.4 Test Assemblies, consisting of two plastic rods, and two
should be prepared in accordance with Practice F86.
flexible spacers, the two-hole plate, two bone screws, one
8. Procedure
beaker, and the rubber cover.
5.4.1 The longer rod is threaded at one end to mate with a
8.1 Test Assembly Preparation (see Fig. 1):
mounting screw, while the other end is threaded to mate with
8.1.1 Clean the plates and screws ultrasonically with deter-
the bone screw.
gent or other degreasing agent to ensure that they are free from
5.4.2 The shorter rod has a reduced diameter at one end to grease and dirt. Rinse them with distilled water, and immedi-
mate with the oscillating horizontal plunger, while the other
ately dry them in warm air.
end is threaded to mate with a bone screw. 8.1.2 Weigh the plate and each screw separately. Then
5.4.3 The flexible spacers made of, for example, polydim-
weigh the three together on a microbalance to an accuracy of
ethylsiloxane or buna-n, are used to maintain axial loads on the 0.01 mg.
screws and to permit the necessary axial displacements asso-
8.1.3 Attach the plates to the posts with the rubber spacers
ciated with the rocking motion of the screws, while at the same and bone screws.Ti
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