ASTM F1798-21

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Designation: F1798 − 13 F1798 − 21
Standard Test Method for
Evaluating the Static and Fatigue Properties of
Interconnection Mechanisms and Subassemblies Used in
Spinal Arthrodesis Implants
This standard is issued under the fixed designation F1798; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the measurement of uniaxial static and fatigue strength, and resistance to loosening of the component
interconnection mechanisms of spinal arthrodesis implants.
1.2 The purpose of this test method is to provide a means of mechanically characterizing different designs of spinal implant
interconnections. Ultimately, the various components and interconnections should be combined for static and fatigue testing of the
spinal implant construct. It is not the intention of this test method to address the analysis of spinal implant constructs or
subconstructs or to define levels of performance of spinal implants, as insufficient knowledge is available to predict the
consequences of the use of particular spinal implant designs.
1.3 This test method sets out definitions for use in measuring standard defines test methods to measure the strength of component
interconnections of spinal implants, possible test methods themselves, and the reporting ofspinal implant component intercon-
nections and how to report test results.
1.4 The values stated in SI units are to be regarded as standard, with the exception of angular measurements, which may be
reported in terms of either degrees or radians.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E4 Practices for Force Calibration and Verification of Testing Machines
F383 Practice for Static Bend and Torsion Testing of Intramedullary Rods (Withdrawn 1996)
This test method is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices. and is the direct responsibility of Subcommittee
F04.25 on Spinal Devices.
Current edition approved Dec. 1, 2013Oct. 1, 2021. Published February 2014October 2021. Originally approved in 1997. Last previous edition approved in 20082013 as
F1798 – 97F1798 – 13.(2008). DOI: 10.1520/F1798-13. 10.1520/F1798-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
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F1798 − 21
F1582F1717 Terminology Relating to Spinal ImplantsTest Methods for Spinal Implant Constructs in a Vertebrectomy Model
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 active length of longitudinal element—the span between rigid supports (for example, 50 mm is the active length in Fig. 1,
Fig. 2, Fig. 3((a),a), Fig. 3((b),b), and Fig. 4.).
3.1.2 global coordinate system—spinal column motion has six degrees of freedom, having translational motion along, and
rotational motion about three axes. The axes are labeled anterior-posterior or a-pA-P (X), medial-lateral or transverse (Y), and
caudal-cranial or axial (Z). This coordinate system is right handed with +X in the anterior direction, +Y towards the left side of
the body, and +Z in the cranial direction. Positive rotations are defined by the right hand rule (see Fig. 5((a)).a)).
3.1.3 gripping capacity—the maximum applied load or moment across an interconnection mechanism within the first 1.5 mm of
permanent displacement or 5° of permanent rotation between the connected components.
3.1.4 local coordinate system—the spine’s global coordinate system shall be applied locally at the position of the interconnection.
The local direction, z, shall be centered through the longitudinal element of the x-y plane. The local direction, x, shall be defined
as parallel to the axis of a screw or back of a hook. The local transverse axis, y, shall be parallel to a transverse element (See(see
Fig. 5((b)b) and Fig. 5((c)).c)).
3.1.5 loosening torque—the torque required to disconnect the various threaded fasteners that might comprise the implant’s
interconnection mechanism.of the spinal arthrodesis implant.
3.1.6 major directions of loading—directions of the predominant forces and moments (relative to the local axes) to which vertebral
connection elements are subjected, (that is, axial load, Fz; A-P load, Fx; axial torsion, Mz; and flexion-extension moment, My).
3.1.6 maximum run out run-out load/moment—the maximum load or moment that can be applied to a subassembly where all the
tested constructs have withstood 2.5 × 106 cycles without a failure.
3.1.7 relevant directions of loading—those directions of loading in which a particular component interconnection is designed to
provide resistance to loading. For example, a particular spinal hook may be designed to withstand a positive axial load, A-P load,
and flexion-extension moment, but not a negative axial load or axial torsion. Hence, positive axial load, A-P load, and
flexion-extension moment are the relevant directions of loading.
FIG. 1 A-P Test Apparatus for Subassembly
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FIG. 2 Transverse Test Apparatus for Subassembly
3.1.8 spinal arthrodesis implant—an implant applied to the spine with the intention of providing that provides temporary
correction and stability to vertebrae while bony fusion occurs.
3.1.9 subassembly failure—permanent deformation resulting from fracture, plastic deformation, loosening, or slippage that renders
the subassembly ineffective or unable to adequately resist load.
3.1.10 subassembly permanent deformation—the displacement (mm) or angular displacement (degree of the subassembly relative
to the unloaded condition) remaining after the applied load moment or torque has been removed. Care must be taken to ensure that
the loading fixtures are rigid and do not contribute to the measurement of deflection.
3.1.11 tightening torque—the specified torque that is applied to the various threaded fasteners that might comprise the implant’s
interconnection mechanism.of the spinal arthrodesis implant during assembly.
3.1.12 ultimate load/moment of the subassembly—maximum load or moment applied to a subassembly (see Point E in Fig. 6).
3.1.13 yield load/moment of the subassembly—the load or moment required to produce a permanent deformation equal to 0.020
times the active length of the longitudinal element (see Point D in Fig. 6).
4. Summary of Test MethodsMethod
4.1 Vertebral attachment components (for example, hook, screws, bands) and transverse elements must be attached to longitudinal
elements (for example, rods, plates) to form spinal implant subassemblies.
4.2 The interconnections are tested only in the relevant directions of loading by applying loads at specific locations relative to the
local coordinate system.
4.3 The interconnections and subassemblies are tested statically in a load-to-failure mode and also can be tested cyclically to
estimate the maximum run out run-out value at 2.5 × 10 cycles.
5. Significance and Use
5.1 Spinal implants are generally composed of several components that, when connected together, form a spinal implant construct.
Spinal implant constructs are designed to provide some stability to the spine while arthrodesis takes place. This test method
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FIG. 3 Flexion-Extension Moment Test Apparatus for Subassembly

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FIG. 4 Transverse Moment Test Apparatus for Subassembly
outlines standardized evaluations of different interconnection mechanisms to facilitate comparison between different designs.
Comparisons must be made cautiously and with careful analysis, taking into account the effects that design differences can have
on the loading configurations.
5.2 This test method is used to quantify the static and fatigue properties of different implant interconnection designs. The
mechanical tests are conducted in vitro using simplified, unidirectional loads and moments. Fatigue testing in a simulated body
fluid or saline may have a fretting, corrosive, or lubricating effect on the interconnection and thereby affect the relative performance
of tested devices. Hence, the test environment, whether a simulated body fluid, saline (9g(9 g NaCl per 1000 mL H O), with a
saline drip, or dry, is an important characteristic of the test and must be reported accurately.
5.3 The loading of spinal implant constructs in vivo will, in general, differ from the loading configurations used in this test method.
The results obtained here cannot be used directly to predict in vivo performance. However, the results can be used to compare
different component designs in terms of relative mechanical parameters.
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FIG. 5 Coordinate System
FIG. 6 Load/Displacement Curve
6. Apparatus
6.1 Machines used for the test shall conform to the requirements of Practices E4.
6.2 The apparatus for axial (z) gripping capacity measurements of an interconnection mechanism is depicted in Fig. 7((a).a). One
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FIG. 7 Axial Gripping Capacity Test Apparatus
end of the longitudinal element shall be clamped rigidly, leaving 5 mm exposed between the interconnection mechanism and the
test machine base. A section of longitudinal element at least 5 mm shall extend beyond the interconnection linkage and remain
unfixed. Axial loads are applied to the interconnection mechanism along the axis of the longitudinal element via a sleeve (collar)
which freely surrounds the longitudinal element. The sleeve (collar) should evenly distribute the load around the interconnection.
An alternate method, depicted in Fig. 7((b),b), applies the load to the longitudinal element and pushes it through the
interconnection clamp.
6.3 The apparatus for A-P (x) mechanical property measurements of a subassembly is depicted in Fig. 1. Both ends of the
longitudinal element shall be clamped rigidly, with the interconnection centered on a 50-mm section of the longitudinal element.
The local origin of the interconnection mechanism shall be centered between the mounts. Loads are applied to the interconnection
(perpendicular to the longitudinal element) via a clamp on the hook, screw, or band. The load should be centered through the local
x coordinate x-coordinate axis.
6.4 The apparatus for transverse (y) mechanical property measurements of a subassembly is depicted in Fig. 2. Both ends of the
longitudinal element shall be clamped rigidly, with the interconnection centered on a 50-mm section of the longitudinal element.
The local origin of the interconnection mechanism shall be centered between the mounts. Loads are applied to the interconnection
(perpendicular to the longitudinal element) via a clamp on the transverse connector. The load should be centered through the local
y coordinate y-coordinate axis.
6.5 The apparatus for flexion-extension moment (My) mechanical property measurements of a subassembly is depicted in Fig. 3.
Both ends of the longitudinal element shall be clamped rigidly, with the interconnection centered on a 50-mm section of the
longitudinal element. The local origin of the interconnection mechanism shall be centered between the mounts. Loads are applied
to the interconnection (parallel to the longitudinal element). For spinal hooks, the load shall be applied via a cylinder set in the
hook notch (see Fig. 3((a)).a)). For other elements (screws) the load shall be applied 25 mm from the local z axis z-axis (see Fig.
3((b)).b)).
6.6 The apparatus for transverse moment (Mx) mechanical property measurements of a subassembly is depicted in Fig. 4. As in
the previous test, 6.5, both ends of the longitudinal element shall be clamped rigidly, with the interconnection centered on a 50-mm
section of the longitudinal element. The local origin of the interconnection mechanism shall be centered between the mounts. Loads
are applied to the interconnection (parallel to the longitudinal element), 25 mm from the z axis.z-axis.
6.7 The apparatus for axial torque (Mz) gripping capacity measurements of an interconnection mechanism is depicted in Fig.
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8((a)a) and is similar to that described in 6.2, with the exception that the axial torque is applied via notches in the sleeve that
surrounds the longitudinal element. An alternative method is to hold the interconnection rigidly and apply the torsional force to
the longitudinal element as shown in Fig. 8((b).b). A third alternative is to apply the torque via a force applied to a moment arm
as shown in Fig. 8((c),c), but this alternative may introduce an additional variable of bending of the anchor component. In any case,
care must be taken to evaluate and minimize the effect of the torsional properties of the longitudinal element on the results.
6.8 For each of these apparatuses, care must be taken to ensure that the loading fixtures are rigid and do not contribute to the
measurement of deflection.
7. Sampling
7.1 The samples tested shall be previously unused parts, and shall not be re-tested.
7.2 The test constructs shall be labeled and maintained according to good laboratory practice.
7.3 Static tests of mechanical properties should have a minimum sample size of five.
7.4 Fatigue tests for determining the maximum run out run-out load or moment of a subassembly at 2.5 × 10 cycles shall utilize
a run down, rundown, half-interval approach with one specimen per run down interval or half-interval and three consecutive
specimens
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