1、Designation: F 1798 97 (Reapproved 2008)Standard Guide forEvaluating the Static and Fatigue Properties ofInterconnection Mechanisms and Subassemblies Used inSpinal Arthrodesis Implants1This standard is issued under the fixed designation F 1798; the number immediately following the designation indica
2、tes the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the measurement of uniaxia
3、l staticand fatigue strength, and resistance to loosening of the com-ponent interconnection mechanisms of spinal arthrodesis im-plants.1.2 The purpose of this guide is to provide a means ofmechanically characterizing different designs of spinal implantinterconnections. Ultimately, the various compon
4、ents and in-terconnections should be combined for static and fatiguetesting of the spinal implant construct. It is not the intention ofthis guide to address the analysis of spinal implant constructsor subconstructs or to define levels of performance of spinalimplants as insufficient knowledge is ava
5、ilable to predict theconsequences of the use of particular spinal implant designs.1.3 This guide sets out definitions for use in measuring thestrength of component interconnections of spinal implants,possible test methods themselves, and the reporting of testresults.1.4 The values stated in SI units
6、 are to be regarded asstandard, with the exception of angular measurements, whichmay be reported in terms of either degrees or radians.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to est
7、ablish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesF 383 Practice for Static Bend and Torsion Testing ofIntramedullary Rods3F 1582 Te
8、rminology Relating to Spinal Implants3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 active length of longitudinal elementthe span be-tween rigid supports (for example, 50 mm is the active lengthin Fig. 1, Fig. 2, Fig. 3(a), Fig. 3(b), and Fig. 4.3.1.2 global coordinate system
9、spinal column motion hassix degrees of freedom, having translational motion along, androtational motion about three axes. The axes are labeledanterior-posterior or a-p (X), medial-lateral or transverse (Y),and caudal-cranial or axial (Z). This coordinate system is righthanded with +X in the anterior
10、 direction, +Y towards the leftside of the body, and +Z in the cranial direction. Positiverotations are defined by the right hand rule (see Fig. 5(a).3.1.3 gripping capacitythe maximum applied load ormoment across an interconnection mechanism within the first1.5 mm of permanent displacement or 5 of
11、permanent rotationbetween the connected components.3.1.4 local coordinate systemthe spines global coordi-nate system shall be applied locally at the position of theinterconnection. The local direction, z, shall be centeredthrough the longitudinal element of the x-y plane. The localdirection, x, shal
12、l be defined as parallel to the axis of a screwor back of a hook. The local transverse axis, y, shall be parallelto a transverse element (See Fig. 5(b) and Fig. 5(c).3.1.5 loosening torquethe torque required to disconnectthe various threaded fasteners that might comprise the im-plants interconnectio
13、n mechanism.3.1.6 major directions of loadingdirections of the pre-dominant forces and moments (relative to the local axes) towhich vertebral connection elements are subjected, (that is,axial load, Fz; A-P load, Fx; axial torsion, Mz; and flexion-extension moment, My).1This guide is under the jurisd
14、iction of ASTM Committee F04 onMedical andSurgical Materials and Devices .Current edition approved Dec. 1, 2008. Published December 2008. Originallyapproved in 1997. Last previous edition approved in 2003 as F 1798 97(2003).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcont
15、act ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.7 maxim
16、um run out load/momentthe maximum loador moment that can be applied to a subassembly where all thetested constructs have withstood 2.5 3 106 cycles without afailure.3.1.8 relevant directions of loadingthose directions ofloading in which a particular component interconnection isdesigned to provide re
17、sistance to loading. For example, aparticular spinal hook may be designed to withstand a positiveaxial load, A-P load, and flexion-extension moment, but not anegative axial load or axial torsion. Hence, positive axial load,A-P load, and flexion-extension moment are the relevantdirections of loading.
18、3.1.9 spinal arthrodesis implantan implant applied to thespine with the intention of providing temporary correction andstability to vertebrae while bony fusion occurs.3.1.10 subassembly failurepermanent deformation result-ing from fracture, plastic deformation, loosening or slippagethat renders the
19、subassembly ineffective or unable to ad-equately resist load.3.1.11 subassembly permanent deformationthe displace-ment (mm) or angular displacement (degree of the subassem-bly relative to the unloaded condition) remaining after theapplied load moment or torque has been removed. Care mustbe taken to
20、ensure that the loading fixtures are rigid and do notcontribute to the measurement of deflection.3.1.12 tightening torquethe specified torque that is ap-plied to the various threaded fasteners that might comprise theimplants interconnection mechanism.3.1.13 ultimate load/moment of the subassemblymax
21、imum load or moment applied to a subassembly (see PointEinFig. 6).3.1.14 yield load/moment of the subassemblythe load ormoment required to produce a permanent deformation equal to0.020 times the active length of the longitudinal element (seePoint D in Fig. 6).4. Summary of Test Methods4.1 Vertebral
22、attachment components (for example, hook,screws, bands) and transverse elements must be attached tolongitudinal elements (for example, rods, plates) to form spinalimplant subassemblies.4.2 The interconnections are tested only in the relevantdirections of loading by applying loads at specific locatio
23、nsrelative to the local coordinate system.4.3 The interconnections and subassemblies are tested stati-cally in a load-to-failure mode and also can be tested cyclicallyto estimate the maximum run out value at 2.5 3 106cycles.5. Significance and Use5.1 Spinal implants are generally composed of several
24、components that, when connected together, form a spinalimplant construct. Spinal implant constructs are designed toprovide some stability to the spine while arthrodesis takesplace. This guide outlines standardized evaluations of differentinterconnection mechanisms to facilitate comparison betweendif
25、ferent designs. Comparisons must be made cautiously andwith careful analysis, taking into account the effects that designdifferences can have on the loading configurations.5.2 This guide is used to quantify the static and fatigueproperties of different implant interconnection designs. Themechanical
26、tests are conducted in vitro using simplified,unidirectional loads and moments. Fatigue testing in a simu-lated body fluid or saline may have a fretting, corrosive, orlubricating effect on the interconnection and thereby affect therelative performance of tested devices. Hence, the test envi-ronment,
27、 whether a simulated body fluid, saline (9g NaCl per1000 mL H2O), with a saline drip, or dry, is an importantcharacteristic of the test and must be reported accurately.5.3 The loading of spinal implant constructs in vivo will, ingeneral, differ from the loading configurations used in thisguide. The
28、results obtained here cannot be used directly topredict in vivo performance. However, the results can be usedto compare different component designs in terms of relativemechanical parameters.FIG. 1 A-P Test Apparatus for SubassemblyFIG. 2 Transverse Test Apparatus for SubassemblyF 1798 97 (2008)2FIG.
29、 3 Flexion-Extension Moment Test Apparatus for SubassemblyF179897(2008)36. Apparatus6.1 Machines used for the test shall conform to the require-ments of Practices E4.6.2 The apparatus for axial (z) gripping capacity measure-ments of an interconnection mechanism is depicted in Fig.7(a). One end of th
30、e longitudinal element shall be clampedrigidly, leaving 5 mm exposed between the interconnectionmechanism and the test machine base.Asection of longitudinalelement at least 5 mm shall extend beyond the interconnectionlinkage and remain unfixed. Axial loads are applied to theinterconnection mechanism
31、 along the axis of the longitudinalelement via a sleeve (collar) which freely surrounds thelongitudinal element. The sleeve (collar) should evenly distrib-ute the load around the interconnection. An alternate method,depicted in Fig. 7(b), applies the load to the longitudinalelement and pushes it thr
32、ough the interconnection clamp.6.3 The apparatus forA-P (x) mechanical property measure-ments of a subassembly is depicted in Fig. 1. Both ends of thelongitudinal element shall be clamped rigidly, with the inter-connection centered on a 50-mm section of the longitudinalelement. The local origin of t
33、he interconnection mechanismshall be centered between the mounts. Loads are applied to theinterconnection (perpendicular to the longitudinal element) viaa clamp on the hook, screw, or band. The load should becentered through the local x coordinate axis.6.4 The apparatus for transverse (y) mechanical
34、 propertymeasurements of a subassembly is depicted in Fig. 2. Bothends of the longitudinal element shall be clamped rigidly, withFIG. 4 Transverse Moment Test Apparatus for SubassemblyF 1798 97 (2008)4FIG. 5 Coordinate SystemF 1798 97 (2008)5the interconnection centered on a 50-mm section of thelong
35、itudinal element. The local origin of the interconnectionmechanism shall be centered between the mounts. Loads areapplied to the interconnection (perpendicular to the longitudi-nal element) via a clamp on the transverse connector. The loadshould be centered through the local y coordinate axis.6.5 Th
36、e apparatus for flexion-extension moment (My) me-chanical property measurements of a subassembly is depictedin Fig. 3. Both ends of the longitudinal element shall beclamped rigidly, with the interconnection centered on a 50-mmsection of the longitudinal element. The local origin of theinterconnectio
37、n mechanism shall be centered between theFIG. 6 Load/Displacement CurveF 1798 97 (2008)6mounts. Loads are applied to the interconnection (parallel tothe longitudinal element). For spinal hooks, the load shall beapplied via a cylinder set in the hook notch (see Fig. 3(a). Forother elements (screws) t
38、he load shall be applied 25 mm fromthe local z axis (see Fig. 3(b).6.6 The apparatus for transverse moment (Mx) mechanicalproperty measurements of a subassembly is depicted in Fig. 4.As in the previous test, 6.5, both ends of the longitudinalelement shall be clamped rigidly, with the interconnection
39、centered on a 50-mm section of the longitudinal element. Thelocal origin of the interconnection mechanism shall be centeredbetween the mounts. Loads are applied to the interconnection(parallel to the longitudinal element), 25 mm from the z axis.6.7 The apparatus for axial torque (Mz) gripping capaci
40、tymeasurements of an interconnection mechanism is depicted inFig. 8(a) and is similar to that described in 6.2 with theexception that the axial torque is applied via notches in thesleeve that surrounds the longitudinal element. An alternativemethod is to hold the interconnection rigidly and apply th
41、etorsional force to the longitudinal element as shown in Fig.8(b). A third alternative is to apply the torque via a forceapplied to a moment arm as shown in Fig. 8(c), but thisalternative may introduce an additional variable of bending ofthe anchor component. In any case, care must be taken toevalua
42、te and minimize the effect of the torsional properties ofthe longitudinal element on the results.7. Sampling7.1 The samples tested shall be previously unused parts, andshall not be re-tested.7.2 The test constructs shall be labeled and maintainedaccording to good laboratory practice.7.3 Static tests
43、 of mechanical properties should have aminimum sample size of five.7.4 Fatigue tests for determining the maximum run out loador moment of a subassembly at 2.5 3 106cycles shall utilize arun down, half-interval approach4with one specimen per rundown interval or half-interval and three consecutive spe
44、cimensshowing run out to 2.5 3 106cycles. Alternative methods fordetermining the starting point of the fatigue curve are therun-up method or choosing 75 % of the ultimate static load ormoment.8. Procedure for Measuring Static Mechanical Properties8.1 Measure the tightening torques for any set screws
45、 ornuts which are incorporated into the interconnection linkage.8.2 Apply all tightening, crimping, or locking mechanismsas specified by the manufacturer.8.3 The recommended maximum rate for applying a load is20 N/s (or 25 mm/min) and is 25 N-m/min (or 25 /min) forapplying a moment or torque. Since
46、rate is machine- andsoftware-dependent, it may be necessary to run the tests slowerto achieve accurate data.8.4 StaticA-P load (Fx), transverse load (Fy), axial grippingcapacity (Fz), and transverse moment (Mx), flexion-extensionmoment (My), and axial torque (Mz) shall be measured usingthe apparatus
47、 described in 6.1-6.7.8.5 Loads and moments need to be measured only in therelevant directions of loading.8.6 After each load or moment measurement, looseningtorque shall be measured (if applicable).4“Optiminal Stress Amplitude Selection in Estimating Median Fatigue LimitsUsing Small Samples”, Littl
48、e, R.E., ed., J. of Testing and Evaluation, ASTM, 1990,pp. 115122.FIG. 7 Axial Gripping Capacity Test ApparatusF 1798 97 (2008)7FIG. 8 Axial Torque Gripping Capacity Test ApparatusF 1798 97 (2008)89. Procedure for the Measurement of Fatigue Run Out9.1 Measure the tightening torques for any set screw
49、s ornuts that are incorporated into the connection linkage.9.2 Apply all tightening, crimping, or locking mechanismsas specified by the manufacturer.9.3 The maximum frequency of cyclic loading is not speci-fied but shall be measured and reported.9.4 All fatigue loading should be sinusoidal, accomplishedvia continuous load amplitude control, rather than in a con-trolled deflection manner.9.5 A-P fatigue run out (Fx), transverse fatigue run out (Fy),axial fatigue run out (Fz), transverse moment fatigue run out(Mx), flexion extension moment fatigue ru
