1、Designation: F 1798 97 (Reapproved 2003)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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the measurement of uniaxi
3、al 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 compo
4、nents 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 av
5、ailable 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 unit
6、s are to be regarded asstandard.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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitati
7、ons prior to use.2. Referenced Documents2.1 ASTM Standards:2E 4 Practices for Force Verification of Testing MachinesE 6 Terminology Relating to Methods of Mechanical Test-ingE 468 Practice for the Presentation of Constant AmplitudeFatigue Test Results from Metallic MaterialsE 739 Practice for Statis
8、tical Analysis of Linear or Linear-ized Stress-Life (S-N) and Strain-Life (e-N) Fatigue DataE 1150 Definitions of Terms Relating to Fatigue3F 383 Practice for Static Bend and Torsion Testing ofIntramedullary Rods3F 1582 Terminology Relating to Spinal Implants3. Terminology3.1 Definitions of Terms Sp
9、ecific 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 systemspinal column motion hassix degrees of freedom, having translational motion al
10、ong, 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 direction, +Y towards the leftside of the body, and +Z in the cranial directi
11、on. 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 permanent rotationbetween the connected components.3.1.4 local coordinate syst
12、emthe 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, shall be defined parallel to the axis of a screw orback of a hook. The local trans
13、verse axis, y, shall be parallel toa 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 interconnection mechanism.3.1.6 major directions of loadingdirections of the pre-dominant force
14、s 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 jurisdiction of ASTM Committee F04 onMedical andSurgical Materials and Devices and is t
15、he direct responsibility of SubcommitteeF04.25 on Spinal Devices .Current edition approved Nov. 1, 2003. Published November 2003. Originallyapproved in 1997. Last previous edition approved in 1997 as F 1798 97.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Custo
16、mer 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 maximum run out loa
17、d/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 resistance to lo
18、ading. 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 relevant directionsof loading.3.1.9 spinal arthr
19、odesis implantan implant applied to thespine with the specific intention of providing temporarycorrection and stability to vertebrae while bony fusion occurs.3.1.10 subassembly failurepermanent deformation result-ing from fracture, plastic deformation, loosening or slippagethat renders the subassemb
20、ly 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 insure the
21、 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 subassemblymaximum load or mo
22、ment applied to a subassembly (see PointE in Fig. 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 attachment co
23、mponents (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 locationsrelative to
24、 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 severalcomponents th
25、at, 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 so that comparison between dif-ferent designs is
26、 facilitated. Comparisons must be madecautiously and with careful analysis, taking into account theeffects that design differences can have on the loading configu-rations.5.2 This guide is used to quantify the static and fatigueproperties of different implant interconnection designs. Themechanical t
27、ests 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, orlubrication effect on the interconnection and thereby affect therelative performance of tested devices. Hence, the test envi-ronment,
28、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 r
29、esults obtained here cannot be used directly topredict in vivo performance. However, the results can be usedFIG. 1 A-P Test Apparatus for SubassemblyFIG. 2 Transverse Test Apparatus for SubassemblyF 1798 97 (2003)2FIG.3Flexion-ExtensionMomentTestApparatusforSubassemblyF 1798 97 (2003)3to compare dif
30、ferent component designs in terms of relativemechanical parameters.6. Apparatus6.1 Machines used for the test shall conform to the require-ments of Practices E 4.6.2 The apparatus for axial (z) gripping capacity measure-ments of an interconnection mechanism is depicted in Fig.7(a). One end of the lo
31、ngitudinal element shall be clampedrigidly, leaving 5 mm exposed between the interconnectionmechanism and the test machine base. A section of longitudinalelement at least 5 mm shall extend beyond the interconnectionlinkage and remain unfixed. Axial loads are applied to theinterconnection mechanism a
32、long 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 throu
33、gh the interconnection clamp.6.3 The apparatus for A-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 th
34、e 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.FIG. 4 Transverse Moment Test Apparatus for Suba
35、ssemblyF 1798 97 (2003)4FIG. 5 Coordinate SystemF 1798 97 (2003)56.4 The apparatus for transverse (y) mechanical propertymeasurements of a subassembly is depicted in Fig. 2. Bothends of the longitudinal element shall be clamped rigidly, withthe interconnection centered on a 50 mm section of thelongi
36、tudinal 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 The
37、 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 theinterconnection
38、 mechanism shall be centered between themounts. 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, Fig. 3(a). For otherFIG. 6 Load/Displacement CurveF 1798 97 (2003)6elements (screws) the lo
39、ad shall be applied 25 mm from thelocal z axis, 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 interconnectioncentered
40、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 capacitymeasure
41、ments 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 thetorsiona
42、l 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 toevaluate and mi
43、nimize the affect of the torsional properties ofthe longitudinal element on the results.7. Sampling7.1 The samples tested shall be previously unused partsonly, and shall not be re-tested.7.2 The test constructs shall be labeled and maintainedaccording to good laboratory practice.7.3 Static tests of
44、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 specime
45、nsshowing 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 orn
46、uts 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 rate
47、 is machine andsoftware dependent, it may be necessary to run the tests slowerto achieve accurate data.8.4 Static A-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 des
48、cribed in 6.1-6.7.8.5 Loads and moments in only the relevant directions ofloading need be measured.8.6 After each load or moment measurement, looseningtorque shall be measured (if applicable).9. Procedure for the Measurement of Fatigue Run Out9.1 Measure the tightening torques for any set screws orn
49、uts that are incorporated into the connection linkage.4See “Optiminal Stress Amplitude Selection in Estimating Median FatigueLimits Using Small Samples”, Little, R.E., ed., J. of Testing and Evaluation, ASTM,1990, pp. 115122.FIG. 7 Axial Gripping Capacity Test ApparatusF 1798 97 (2003)7FIG. 8 Axial Torque Gripping Capacity Test ApparatusF 1798 97 (2003)89.2 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 fatig
