1、Designation: F897 02 (Reapproved 2013)Standard Test Method forMeasuring Fretting Corrosion of Osteosynthesis Plates andScrews1This standard is issued under the fixed designation F897; the number immediately following the designation indicates the year of originaladoption or, in the case of revision,
2、 the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method provides a screening test for determin-ing the amount of metal loss from plates and scre
3、ws used forosteosynthesis (internal fixation of broken bones) due tofretting corrosion in the contact area between the screw headand the plate hole countersink area. The implants are used inthe form they would be used clinically. The machine describedgenerates a relative motion between plates and sc
4、rews whichsimulates one type of motion pattern that can occur when thesedevices are used clinically.1.2 Since the environmental and stress conditions used inthis test method may not be identical to those experienced bybone plates in the human body, this test method may producefretting corrosion rate
5、s that are lower or higher than thoseexperienced in practice. The recommended axial load of 400 Nwas selected as being in a range where the amount of frettingcorrosion is not sensitive to small changes in axial load (1).2The combination of the recommended load and angular dis-placement are such that
6、 a measurable amount of frettingcorrosion of surgical alloys occurs in a comparatively shortperiod of time (7 to 14 days). (Refs 1-3)1.3 The device is designed so as to facilitate sterilization ofthe test specimens and test chambers to permit testing withproteinaceous solutions that would become con
7、taminated withmicrobial growth in nonsterile conditions.1.4 The specimens used can be standard osteosynthesisimplants or can be materials fabricated into the appropriateshapes.1.5 This test method may be used for testing the frettingcorrosion of metal plates and screws of similar or differentalloy c
8、ompositions, or it may be used for testing the frettingcorrosion of metal-nonmetal combinations. This test methodmay also be used for wear or degradation studies of nonme-tallic materials. This test method may be used as a screeningtest to rank the corrosivities of saline or proteinaceoussolutions,
9、or to rank metal-to-metal couples for resistance tofretting corrosion, or to study other material combinations.1.6 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem sh
10、all be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.7 This standard may involve hazardous materials,operations, and equipment. This standard does not purport toaddress all of the safety concerns associated with its use. It ist
11、he responsibility of whoever uses this standard to consult andestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D1886 Test Methods for Nickel in WaterF86 Practice for Surface Preparatio
12、n and Marking of Metal-lic Surgical ImplantsF382 Specification and Test Method for Metallic Bone PlatesF543 Specification and Test Methods for Metallic MedicalBone ScrewsG1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test Specimens3. Summary of Test Method3.1 A two-hole plate is atta
13、ched to two plastic rods withbone screws, with flexible spacers between the plate and therods, placed in a glass beaker, and the beaker sealed with aflexible rubber cover. This assembly is steam sterilized, andthen a sterile solution is injected through the rubber cover intothe beaker. This assembly
14、 is then mounted in the frettingapparatus which, when set in motion, produces a rockingmotion and, therefore, a small cyclic displacement between the1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devicesand is the direct responsibility of Subco
15、mmitteeF04.15 on Material Test Methods.Current edition approved March 1, 2013. Published March 2013. Originallyapproved in 1984. Last previous edition approved in 2007 as F897 02(2007). DOI:10.1520/F0897-02R13.2The boldface numbers in parentheses refer to the list of references at the end ofthis sta
16、ndard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO
17、 Box C700, West Conshohocken, PA 19428-2959. United States1mating surfaces of the plate and screws. The amount of frettingcorrosion is determined at the end of the test by measurementof the weight loss of the plates and screws and by chemicalanalysis of the solutions.4. Significance and Use4.1 It is
18、 well known from examination of implants after usethat plates and screws used for osteosynthesis are subjected tometal loss due to corrosion at the plate-screw interfaces. One ofthe mechanisms of this corrosive attack is fretting corrosiondue to relative motion (micromotion) between the screw headsa
19、nd plate-hole countersinks.4.2 It is also known that release of corrosion products intothe tissues surrounding an implant may have adverse effects onlocal tissue or have systemic effects. Thus, it is important tominimize the amount of tissue exposure to corrosion products.4.3 Screws and plates are a
20、vailable in different configura-tions in accordance with Specifications F543 and F382. Thistest method may be used to evaluate the effects of differentcombinations of screw and plate designs.As new materials anddevice designs are developed for use in the treatment offractured bones, it is important
21、to determine the effects thesedevelopments have on the amount of metal loss due to frettingcorrosion.4.4 This test method provides a standardized screening testfor ranking metal plates and screws in terms of resistance tofretting corrosion and for determining the influence of differentsolutions on f
22、retting corrosion rates.4.5 This test method may also be used to generate corrosionproducts either for chemical analysis of the products or fortesting for biological reactions to corrosion products usinganimal or cell culture methods.4.6 It is well known that fretting corrosion rates depend onnormal
23、 load or pressure, frequency, sliding amplitude,materials, surface treatments, and environmental factors. (4)Therefore, when determining the effect of changing one ofthese parameters (for example, material or environment), allothers must be kept constant to facilitate interpretation of theresults.5.
24、 Apparatus5.1 Steam Autoclave, capable of maintaining 121 6 2C250 6 4F, and equipped with a thermometer, pressuregauge, vent cock, and a rack to hold the test assemblies abovethe water level.5.2 Microbalance, with a 0.01-mg scale.5.3 Fretting Apparatus, as described in 5.3.1-5.3.4 andillustrated in
25、Fig. 1 and Fig. 2.5.3.1 The fretting apparatus is driven by a slow speed gearmotor connected to a horizontal rotating shaft. Round diskswith machined flats (cams) are mounted on the shaft as shownin Fig. 1. For multiple specimen testing, there may be morethan one cam on the drive shaft.5.3.2 The fla
26、ts on the cams are machined so as to produce 2of relative motion between the posts of the test assemblies.NOTE 1A suggested combination of short post length and plungerdisplacement is a 5-cm post with a 1.9-mm displacement.5.3.3 The shaft rotation rate and the number of machinedflats shall be such t
27、hat the flats produce one oscillation of theplunger per second.NOTE 1Figure 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 SystemF897 02 (2013)2
28、5.3.4 Test assembly holding and driving frames are mountedsymmetrically on each side of the rotating cams. The oscillat-ing plunger is springloaded and held in the guide sleeve. Thehole in the top plate is slotted to permit adjustment of theposition of the test assemblies.5.4 Test Assemblies, consis
29、ting of two plastic rods, and twoflexible spacers, the two-hole plate, two bone screws, onebeaker, and the rubber cover.5.4.1 The longer rod is threaded at one end to mate with amounting screw, while the other end is threaded to mate withthe bone screw.5.4.2 The shorter rod has a reduced diameter at
30、 one end tomate with the oscillating horizontal plunger, while the otherend is threaded to mate with a bone screw.5.4.3 The flexible spacers made of, for example, polydim-ethylsiloxane or buna-n, are used to maintain axial loads on thescrews and to permit the necessary axial displacements asso-ciate
31、d with the rocking motion of the screws, while at the sametime preventing fatigue failure of the screws. The screws aretightened such that there is a 400 6 50 N load on the screws;a different load may be used, but in such cases the load must bereported (see 10.1). In actual operation, it may be easi
32、er tomeasure the screw torque rather than the axial load; a methodfor determining the relationships between torque and load isgiven in Appendix X2.5.4.4 Test Specimen Plates and Screws, as described inSection 7.5.4.5 Beakers, autoclavable borosilicate glass.5.4.6 Rubber Cover, made from a thin piece
33、 of flexiblerubber with two holes punched out to make a tight fit aroundthe plastic rods. Heavy gauge (0.3 mm thick) latex dental damhas been used effectively for this purpose. The cover is securedto the beaker with wire, rubber bands, or by some otherappropriate device.6. Reagents and Materials6.1
34、The basic test solution shall be 0.9 % NaCl in distilledwater. Measure the pH of the solutions before conducting thetest. If necessary, buffer them to ensure they are in the range of6.5 to 7.5.6.2 Other solutions may include other “physiologic” salineand electrolyte solutions for injection (USP) or
35、saline andprotein solutions. If proteins are used, the solutions shall besterile in accordance with 8.1.5. Protein solutions may either bepurchased sterile, or sterilized by filtration. These shall bereported in accordance with 10.1.7. Test Specimens7.1 Plates:7.1.1 The plates used for these tests m
36、ay be cut fromcommercially available plates for osteosynthesis.7.1.2 Plates may be fabricated from 3.5-mm or thicker metalsheet or strip. Holes may be prepared in accordance withSpecification F382. Holes may be round, or slotted, or “self-compressing” type.7.2 Screws:7.2.1 Screws used for this test
37、may be commercially avail-able bone screws. Heads should be spherical, although othershapes may be used.7.2.2 Screws may be fabricated from rod stock in accor-dance with Specification F543.7.3 Test specimens may be used in the condition as receivedfrom the implant manufacturer; custom fabricated spe
38、cimensshould be prepared in accordance with Practice F86.8. Procedure8.1 Test Assembly Preparation (see Fig. 1):8.1.1 Clean the plates and screws ultrasonically with deter-gent or other degreasing agent to ensure that they are free fromgrease and dirt. Rinse them with distilled water, and immedi-ate
39、ly dry them in warm air.8.1.2 Weigh the plate and each screw separately. Thenweigh the three together on a microbalance to an accuracy of0.01 mg.8.1.3 Attach the plates to the posts with the rubber spacersand bone screws. Tighten the screws so as to create a 400 6 50N axial load on the screws. After
40、 a correlation has beendeveloped for relating torque and axial load for the particularmetal(s), screw head, and plate hole configuration used, deter-mine the load indirectly by measurement of the screw torque.8.1.4 Place the assembled test specimens in a borosilicatebeaker, add the test solution, an
41、d seal the top with the rubbercover with the tops of the posts projecting through the gasket.8.1.5 If the test solution contains proteins that might supportmicrobial growth, then the test assembly and solution must besterile. Steam sterilize the test assembly for 20 min at 121Cprior to adding the li
42、quid. Inject the sterile test liquid into thebeaker using a sterile syringe and needle by carefully openinga small space between the post and the gasket.8.2 Test Assembly Mounting:8.2.1 Mate the short plastic rod to the horizontal plunger,and attach the longer rod to the top plate of the assembly ho
43、lderwith the mounting screw.8.2.2 Start the motor and check that there is full motion ofthe horizontal plunger. It may be found that the elastic recoil ofthe elastomeric spacers is such that the plunger springs do notmaintain plunger-cam contact during the complete oscillationcycle. Adjust the posit
44、ion of the mounting screw to ensure thatcontact is maintained. Run the test continuously for one millioncycles. If the test is not run continuously, report details of allinteruptions.FIG. 2 Assembled Test Chamber with Rubber SealF897 02 (2013)38.3 Test Completion:8.3.1 At the completion of the desig
45、nated number of days offretting corrosion, stop the motor and remove the test assembly.8.3.2 Remove the gasket seal, and remove the screws andplates from the spacers and plastic rods.8.3.3 Ultrasonically clean the test specimens in their testliquids to remove all excess corrosion products.8.3.4 Pour
46、 the test liquid and residue into a screw capcontainer, measure the pH of the solution, and store the liquidfor chemical analysis. If the solutions contain organicmaterials, the container should be sterile. Determine theconcentration of the appropriate metals by atomic absorptionspectrophotometry. T
47、he concentration of nickel may be deter-mined in accordance with Test Methods D1886.8.3.5 Ultrasonically clean the plates and screws in detergentand rinse with distilled water. Dry with warm air prior toreweighing. Additional cleaning with a stronger solution maybe necessary, for example, with 10 %
48、oxalic acid or othersolutions in accordance with Practice G1.8.3.6 Weigh the plates and screws separately. Then weighthem together on a microbalance to an accuracy of 0.01 mg.9. Calculation or Interpretation of Results9.1 Calculate the change in weight of the plate and eachscrew separately, and as a
49、 total weight loss when the three areweighed together.10. Report10.1 The report shall contain a detailed description of thematerials used for manufacture of the plate and screws, forexample, chemical composition, grain size, hardness, andinclusion content, the design and dimensions of the plate andscrews, the surface condition of the metal(s), the axial load onthe screws if other than 400 6 50 N, the pH before and afterthe test and the composition of the test solution, and the detailsof the fretting cycle and type of cleaning solution used.10.2 Report the amount of frettin
