ASTM F2346-18

Standard Test Methods for Static and Dynamic Characterization of Spinal Artificial Discs

SIGNIFICANCE AND USE
5.1 Artificial intervertebral discs are orthopaedic implants that replace degenerated natural intervertebral discs. Their function is to support the anterior column of the spine while allowing motion at the operated level. These test methods outline materials and methods for the characterization of the mechanical performance of different artificial intervertebral discs so that comparisons can be made between different designs.  
5.2 These test methods are designed to quantify the static and dynamic characteristics of different designs of artificial intervertebral discs. These tests are conducted in vitro in order to allow for analysis of individual disc replacement devices and comparison of the mechanical performance of multiple artificial intervertebral disc designs in a standard model.  
5.3 The loads applied to the artificial intervertebral discs may differ from the complex loading seen in vivo, and therefore, the results from these tests may not directly predict in vivo performance. The results, however, can be used to compare mechanical performance of different artificial intervertebral discs.  
5.4 Fatigue tests should be conducted in a 0.9 % saline environmental bath at 37°C at a rate of 2 Hz or less. Other test environments such as a simulated body fluid, a saline drip or mist, distilled water, or other type of lubrication could also be used with adequate justification. Likewise, alternative test frequencies may be used with adequate justification.  
5.5 It is well known that the failure of materials is dependent upon stress, test frequency, surface treatments, and environmental factors. Therefore, when determining the effect of changing one of these parameters (for example, frequency, material, or environment), all others should be kept constant to facilitate interpretation of the results. In particular, it may be necessary to assess the influence of test frequency on device fracture while holding the test environment, implant materials and processing, ...
SCOPE
1.1 These test methods specify the materials and methods for the static and dynamic testing of artificial intervertebral discs.  
1.2 These test methods are intended to provide a basis for the mechanical comparison among past, present, and future non-biologic artificial intervertebral discs. These test methods allow comparison of artificial intervertebral discs with different intended spinal locations (cervical, thoracic, and lumbar) and methods of application to the intervertebral spaces. These test methods are intended to enable the user to mechanically compare artificial intervertebral discs and do not purport to provide performance standards for artificial intervertebral discs.  
1.3 These test methods describe static and dynamic tests by specifying load types and specific methods of applying these loads. These tests are designed to allow for the comparative evaluation of artificial intervertebral discs.  
1.4 These test methods do not purport to address all clinically relevant failure modes for artificial intervertebral discs, some of which will be device specific. For example, these test methods do not address the implant's resistance to expulsion or implant wear resistance under expected in vivo loads and motions. In addition, the biologic response to wear debris is not addressed in these test methods.  
1.5 Requirements are established for measuring displacements, determining the yield load or moment, and evaluating the stiffness of artificial intervertebral discs.  
1.6 Some artificial intervertebral discs may not be testable in all test configurations.  
1.7 The values stated in SI units are to be regarded as the standard with the exception of angular measurements, which may be reported in terms of either degrees or radians.  
1.8 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 approp...

General Information

• Status: Published
• Publication Date: 31-May-2018
• ICS: 11.040.40 - Implants for surgery, prosthetics and orthotics
• Technical Committee: F04 - Medical and Surgical Materials and Devices
• Drafting Committee: F04.25 - Spinal Devices

Relations

• Replaces: ASTM F2346-05(2011) - Standard Test Methods for Static and Dynamic Characterization of Spinal Artificial Discs
• Effective Date: 01-Jun-2018
• Refers: ASTM E1823-24a - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Feb-2024
• Refers: ASTM E1823-24 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2024
• Refers: ASTM E1823-20 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2020
• Refers: ASTM F2077-17 - Test Methods For Intervertebral Body Fusion Devices
• Effective Date: 01-Oct-2017
• Refers: ASTM F1582-98(2016) - Standard Terminology Relating to Spinal Implants
• Effective Date: 01-Oct-2016
• Refers: ASTM F2077-14 - Test Methods For Intervertebral Body Fusion Devices
• Effective Date: 01-Oct-2014
• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014
• Refers: ASTM E1823-12e - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Dec-2012
• Refers: ASTM E1823-12d - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Nov-2012
• Refers: ASTM E1823-12c - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Sep-2012
• Refers: ASTM E1823-12b - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Aug-2012
• Refers: ASTM E1823-12a - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-May-2012
• Refers: ASTM E1823-12 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Mar-2012
• Refers: ASTM F1582-98(2011) - Standard Terminology Relating to Spinal Implants
• Effective Date: 01-Dec-2011

Overview

ASTM F2346-18 is the international standard published by ASTM International for the static and dynamic mechanical testing of artificial intervertebral discs. These discs are medical implants designed to replace degenerated natural discs in the spine, supporting structural integrity while enabling motion at the treated spinal segment. The standard outlines uniform methods to quantify and compare the mechanical performance of artificial discs, regardless of their intended spinal location (cervical, thoracic, or lumbar) or design features. The procedures detailed in ASTM F2346-18 enable manufacturers, researchers, and regulatory bodies to benchmark new and existing spinal disc designs under standardized laboratory conditions.

Key Topics

• Mechanical Characterization:

  • Provides test methods for static (single-event load) and dynamic (cyclic load) evaluation.
  • Specifies requirements for measuring displacement, yield load or moment, and stiffness.

• Comparative Evaluation:

  • Enables side-by-side comparison of artificial discs across designs, intended spinal levels, and application methods.
  • Facilitates consistent benchmarking for both current and future non-biologic artificial intervertebral discs.

• Test Environments and Apparatus:

  • Recommends in vitro testing in environments simulating physiological conditions (e.g., saline bath at 37°C).
  • Mandates controlled loads and test setups for compression, shear, and torsional testing.

• Standardization and Reporting:

  • Focuses on repeatability and transparency in methodological details.
  • Outlines reporting practices for test parameters, device characteristics, and observed mechanical failures.

Applications

• Product Development and Quality Assurance:
  ASTM F2346-18 is essential in the evaluation of artificial spinal disc implants prior to clinical use. Manufacturers use these test methods to:

  • Assess and optimize mechanical durability and fatigue resistance of disc designs.
  • Identify functional failure modes and mechanical deterioration under simulated physiological loads.
  • Compare performance metrics such as yield load, ultimate load, and stiffness to support regulatory submissions and marketing claims.

• Regulatory and Compliance:
  Regulatory agencies often reference ASTM F2346-18 as a foundational standard for preclinical testing of spinal disc replacement devices. The standardized methods:

  • Support objective device comparison in accordance with recognized international practices.
  • Ensure that critical mechanical properties are thoroughly evaluated and documented.

• Academic and Clinical Research:
  Researchers leverage this standard to:

  • Generate reproducible, peer-reviewed data on the mechanical behavior of spinal implants.
  • Explore the influence of design, materials, and testing conditions on device performance.

Note: While ASTM F2346-18 provides robust comparative data, it does not establish clinical performance benchmarks or address all failure modes specific to implanted devices, such as wear resistance or biological response to debris.

Related Standards

• ASTM E4: Practices for Force Verification of Testing Machines
• ASTM E6: Terminology Relating to Methods of Mechanical Testing
• ASTM E466: Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials
• ASTM E467: Practice for Verification of Constant Amplitude Dynamic Forces in Axial Fatigue Testing Systems
• ASTM E468: Practice for Presentation of Constant Amplitude Fatigue Test Results for Metallic Materials
• ASTM E1823: Terminology Relating to Fatigue and Fracture Testing
• ASTM F1582: Terminology Relating to Spinal Implants
• ASTM F2077: Test Methods for Intervertebral Body Fusion Devices

These related standards provide additional terminology, apparatus guidelines, and analytical methodologies relevant to the mechanical testing and evaluation of spinal implants and orthopedic devices.

---

Keywords: artificial intervertebral disc, static test methods, dynamic test methods, spinal implants, spinal disc testing, ASTM F2346-18, orthopaedic implants, mechanical characterization, fatigue testing, medical device evaluation.

Standards Content (Sample)

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.
Designation:F2346 −18
Standard Test Methods for
Static and Dynamic Characterization of Spinal Artificial
Discs
This standard is issued under the fixed designation F2346; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.8 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 These test methods specify the materials and methods
responsibility of the user of this standard to establish appro-
for the static and dynamic testing of artificial intervertebral
priate safety, health, and environmental practices and deter-
discs.
mine the applicability of regulatory limitations prior to use.
1.2 These test methods are intended to provide a basis for
1.9 This international standard was developed in accor-
the mechanical comparison among past, present, and future
dance with internationally recognized principles on standard-
non-biologic artificial intervertebral discs. These test methods
ization established in the Decision on Principles for the
allowcomparisonofartificialintervertebraldiscswithdifferent
Development of International Standards, Guides and Recom-
intended spinal locations (cervical, thoracic, and lumbar) and
mendations issued by the World Trade Organization Technical
methods of application to the intervertebral spaces. These test
Barriers to Trade (TBT) Committee.
methods are intended to enable the user to mechanically
compare artificial intervertebral discs and do not purport to 2. Referenced Documents
provide performance standards for artificial intervertebral
2.1 ASTM Standards:
discs.
E4Practices for Force Verification of Testing Machines
1.3 These test methods describe static and dynamic tests by E6Terminology Relating to Methods of MechanicalTesting
specifying load types and specific methods of applying these E466Practice for Conducting Force Controlled Constant
loads. These tests are designed to allow for the comparative
Amplitude Axial Fatigue Tests of Metallic Materials
evaluation of artificial intervertebral discs. E467Practice for Verification of Constant Amplitude Dy-
namic Forces in an Axial Fatigue Testing System
1.4 These test methods do not purport to address all clini-
E468Practice for Presentation of Constant Amplitude Fa-
cally relevant failure modes for artificial intervertebral discs,
tigue Test Results for Metallic Materials
some of which will be device specific. For example, these test
E1823TerminologyRelatingtoFatigueandFractureTesting
methodsdonotaddresstheimplant’sresistancetoexpulsionor
F1582Terminology Relating to Spinal Implants
implant wear resistance under expected in vivo loads and
F2077Test Methods for Intervertebral Body Fusion Devices
motions.Inaddition,thebiologicresponsetoweardebrisisnot
addressed in these test methods.
3. Terminology
1.5 Requirements are established for measuring
3.1 All definitions below supersede definitions contained
displacements, determining the yield load or moment, and
within Terminologies E6, E1823, F1582, and Practices E466,
evaluating the stiffness of artificial intervertebral discs.
E467.
1.6 Some artificial intervertebral discs may not be testable
3.2 Definitions:
in all test configurations.
3.2.1 artificial intervertebral disc—asyntheticstructurethat
1.7 The values stated in SI units are to be regarded as the
is permanently implanted in the disc space between two
standard with the exception of angular measurements, which adjacentvertebralbodiestoprovidespinalcolumnsupportand
may be reported in terms of either degrees or radians.
allow intervertebral motion.
3.2.2 coordinate system/axes—three orthogonal axes are
defined by Terminology F1582. The center of the coordinate
These test methods are 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. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved June 1, 2018. Published August 2018. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2005. Last previous edition approved in 2011 as F2346–05 (2011). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/F2346-18. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2346−18
FIG. 1Intervertebral Height Diagram
system is located at the geometric center of the artificial 3.2.8 intervertebral height—the minimum distance parallel
intervertebraldisc.Alternativecoordinatesystemsmaybeused to the Z-axis in the YZ-plane between the unaltered simulated
with justification. The XY-plane is to bisect the superior and vertebral bodies: minimum height of 2 mm and maximum
3,4
inferior surfaces that are intended to simulate the adjacent height of 16.5 mm. See Fig. 1.
vertebral end plates. The positive Z-axis is to be directed
3.2.9 load point—the point through which the resultant
perpendicular to the bisector of the disc space, oriented in the
force on the intervertebral device passes; that is, the geometric
superior direction. The positive X-axis is parallel to the
center of the superior fixture’s sphere (see Figs. 2-4).
intervertebral space, oriented in the anterior direction and the
3.2.10 maximum run-out load or moment—the maximum
positive Y-axis is parallel to the disc space, oriented in the left
load or moment for a given test that can be applied to an
direction. Force components parallel to the XY-plane are shear
artificial intervertebral disc where all of the tested constructs
components of loading.The compressive axial force is defined
have withstood 10000000 cycles without functional failure.
tobethecomponentinthenegative Zdirection.Torsionalload
3.2.11 mechanical deterioration—deterioration that is vis-
is defined to be the component of moment parallel to the
ibletothenakedeyeandisassociatedwithmechanicaldamage
Z-axis.
tothedeviceundertest(forexample,initiationoffatiguecrack
3.2.3 fatigue life—thenumberofcycles, N,thattheartificial
or surface wear).
intervertebral disc can sustain at a particular load or moment
3.2.12 offset angular displacement—(distance OB—Fig. 6)
before functional failure occurs.
offset on the angular displacement axis equal to 2% of the
3.2.4 functional failure—permanent deformation that ren-
intervertebralheight, H,dividedbythemaximumradiusofthe
ders the artificial intervertebral disc ineffective or unable to
implant in the XY-plane; for example, for an artificial interver-
adequately resist load.
tebral disc with a height of 10 mm and a maximum radius in
3.2.5 ideal insertion location—the location of the artificial
the XY-planeof9mm,distanceOB=(0.02)(10mm)/(9mm)
disc in the intervertebral space that is suggested in the
= 0.022 radians = 1.3°.
manufacturer’s surgical installation instructions. The ideal
3.2.13 offset displacement—(distance OB—Fig. 6) offset on
insertion location is to be described with respect to the
the linear displacement axis equal to 2% of the intervertebral
simulated inferior and superior vertebral bodies (polyacetal or
height (for example, 0.2 mm for a 10 mm intervertebral
metal blocks) and will be dictated by the device design.
height).
3.2.6 intended method of application—artificial interverte-
3.2.14 permanent deformation—the remaining linear or an-
bral discs may contain different types of features to stabilize
gular displacement (axial—mm, angular—degrees or radians)
the implant-tissue interface such as threads, spikes, and tex-
relative to the initial unloaded condition of the artificial
tured surfaces. Each type of feature has an intended method of
intervertebral disc after the applied load or moment has been
application or attachment to the spine.
removed.
3.2.7 intended spinal location—the anatomic region of the
3.2.15 stiffness (axial—n/mm, angular—n·mm/degree or
spine intended for the artificial intervertebral disc. Artificial
n·mm/radian)—the slope of the initial linear portion of the
intervertebraldiscsmaybedesignedanddevelopedforspecific
regions of the spine such as the cervical, thoracic, and lumbar
Nissan, M., Gilad, I., “The Cervical and LumbarVertebrae—AnAnthropomet-
spine. Also, since different surgical approaches may exist, the
ric Model,” Engineering In Medicine, Vol 13, No. 3, 1984, pp. 111–114.
description of the intended spinal location should include both
Lu, J., Ebraheim, N.A., Yang, H., Rollins, J., and Yeasting, R. A., “Anatomic
the indicated spinal levels and the ideal insertion locations
BasesforAnteriorSpinalSurgery:SurgicalAnatomyoftheCervicalVertebralBody
within the intervertebral space allowed at each level. and Disc Space,” Surg Radiol Anat, Vol 21, No. 4, 1999, pp. 235–239.
F2346−18
FIG. 2Compression Testing Configuration
load-displacement curve or the slope of the initial linear offset displacement or offset angular displacement. This is
portion of the moment-angular displacement curve. This is illustrated as the distance OA in Fig. 6.
illustrated as the slope of the line OG in Fig. 6. If the device
3.2.20 yield load or moment—the applied load, F,or
does not exhibit a linear initial load/displacement curve, the
moment, M, transmitted by the pushrod (assumed equal to
displacement should be reported at 30%, 60%, and 90% of
force component parallel to and indicated by load or torque
the yield load or moment.
cell) required to produce a permanent deformation equal to the
3.2.16 test block—the component of the test apparatus for offset displacement or the offset angular displacement. This is
mounting the artificial intervertebral disc in the intended test illustrated as point D in Fig. 6.
configuration.
4. Summary of Test Methods
3.2.17 ultimate displacement (axial—mm, angular—
4.1 These test methods are proposed for the mechanical
degrees or radians)—the linear or angular displacement asso-
testing of artificial intervertebral discs specific to the cervical,
ciated with the ultimate load or ultimate moment. This is
thoracic, and lumbar spine.
illustrated as the displacement, OF, in Fig. 6.
4.2 All tests are to be performed on the prosthesis size with
3.2.18 ultimate load or moment (axial—n, angular—
the smallest safety factor for the levels indicated for implan-
n·mm)—the maximum applied load, F, or moment, M, trans-
tation. If this worst-case size cannot be determined using
mitted by the pushrod (assumed equal to force and moment
theoretical or experimental methods such as simple stress
component parallel to and indicated by load or torque cell) to
calculations or finite element analysis, then all available sizes
the artificial intervertebral disc assembly. This is illustrated as
are to be tested and the complete range of results are to be
point E in Fig. 6.
reported.
3.2.19 yield displacement—the linear displacement (mm) or
angular displacement (degrees or radians) when an artificial 4.3 Fatigue testing of the artificial intervertebral discs will
intervertebral disc has a permanent deformation equal to the simulate a motion segment via a gap between two polyacetal
F2346−18
FIG. 3Compression/Shear Testing Configuration
test blocks. The polyacetal will eliminate the effects of the function is to support the anterior column of the spine while
variability of bone properties and morphology for the fatigue allowing motion at the operated level. These test methods
tests. The minimum ultimate tensile strength of the polyacetal outline materials and methods for the characterization of the
blocks shall be no less than 61 MPa. mechanical performance of different artificial intervertebral
discs so that comparisons can be made between different
4.4 Static testing of the artificial intervertebral discs will
designs.
simulate a motion segment via a gap between two stainless
steel blocks. The minimum tensile yield strength of the blocks 5.2 These test methods are designed to quantify the static
shall be no less than 1170 MPa.
and dynamic characteristics of different designs of artificial
intervertebral discs. These tests are conducted in vitro in order
4.5 The pushrod shall be manufactured from stainless steel
toallowforanalysisofindividualdiscreplacementdevicesand
having minimum tensile yield stress of 1170 MPa and be of
comparison of the mechanical performance of multiple artifi-
minimum cross-sectional area that would produce a compres-
cial intervertebral disc designs in a standard model.
sive yield strength of at least 25000 N.
5.3 The loads applied to the artificial intervertebral discs
4.6 Static and dynamic tests will evaluate the artificial
may differ from the complex loading seen in vivo, and
intervertebral disc. The user of these test methods must decide
therefore, the results from these tests may not directly predict
which series of tests are applicable to the artificial interverte-
in vivo performance. The results, however, can be used to
bral disc in question. The user of these test methods may
compare mechanical performance of different artificial in-
choose to use all or a selection of the tests described in these
tervertebral discs.
test methods for testing a particular artificial intervertebral
disc. For example, the torsion test method may not apply to a 5.4 Fatigue tests should be conducted in a 0.9% saline
device that has no mechanical resistance in axial rotation.
environmental bath at 37°C at a rate of 2 Hz or less. Other test
environments such as a simulated body fluid, a saline drip or
5. Significance and Use
mist, distilled water, or other type of lubrication could also be
5.1 Artificial intervertebral discs are orthopaedic implants used with adequate justification. Likewise, alternative test
that replace degenerated natural intervertebral discs. Their frequencies may be used with adequate justification.
F2346−18
FIG. 4Torsion Testing Configuration with a Pin-Slot Gimbal
FIG. 5Polyacetal or Metal Test Block
5.5 It is well known that the failure of materials is depen- changing one of these parameters (for example, frequency,
dent upon stress, test frequency, surface treatments, and envi- material,orenvironment),allothersshouldbekeptconstantto
ronmental factors. Therefore, when determining the effect of facilitate interpretation of the results. In particular, it may be
F2346−18
FIG. 6Typical Load Displacement Curve
necessary to assess the influence of test frequency on device methods should select the intervertebral height that is appro-
fracture while holding the test environment, implant materials priate for the device being tested.
and processing, and implant geometry constant.
6.3 Axial Compression Test Apparatus:
6.3.1 Theactuatorofthetestingmachineisconnectedtothe
6. Apparatus
pushrodbyaminimalfrictionball-and-socketjointoruniversal
6.1 Test machines will conform to the requirements of
joint (that is, unconstrained in bending). The pushrod is
Practices E4.
connected to the superior fixture by a minimal friction sphere
6.2 The intervertebral height, H, shall be determined from joint (that is, unconstrained in bending and torsion). The
hollow pushrod should be of minimal weight so as to be
vertebral body and disc morphometric data at the intended
level of application. Suggested heights are as follows: 4 mm considered a “two force” member.
for the cervical spine, 6 mm for the thoracic spine, and 10 mm 6.3.2 It thus applies to the artificial intervertebral disc a
forthelumbarspine.Theintervertebralheightshouldnotreach resultant force directed along the pushrod’s axis and located at
zeropriortotheonsetoffunctionalfailuredeterioration.Ifthis the center of the superior fixture’s sphere joint (the geometric
occurs, the test is considered a failure. The user of these test center of the device being tested).
F2346−18
6.3.3 For the fatigue tests, the device is placed between two pushrod interconnections. The actuator of the testing machine
polyacetal blocks, which are rigidly attached to the metal mustbeconnectedtothepushrodbyaminimalfriction(thatis,
blocks (Fig. 5). unconstrainedinbending)universaljointtobeabletotransmit
6.3.4 Forthestatictests,metalblocksaretobeused,which torsional moment in addition to axial load. The pushrod is
could be incorporated as an integral part of the superior and connected to the superior fixture by a spherical gimbal mecha-
inferior fixtures. The blocks are to have surfaces that mate nismtoapplycombinedcompressiveforce, F,andmoment, M,
geometrically with the intervertebral disc prosthesis similar to with negligible bending moment to the artificial intervertebral
how the device is intended to mate with vertebral end plates. disc.
6.3.5 The te
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F2346 − 05 (Reapproved 2011) F2346 − 18
Standard Test Methods for
Static and Dynamic Characterization of Spinal Artificial
Discs
This standard is issued under the fixed designation F2346; 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 These test methods specify the materials and methods for the static and dynamic testing of artificial intervertebral discs.
1.2 These test methods are intended to provide a basis for the mechanical comparison among past, present, and future
non-biologic artificial intervertebral discs. These test methods allow comparison of artificial intervertebral discs with different
intended spinal locations (cervical, thoracic, and lumbar) and methods of application to the intervertebral spaces. These test
methods are intended to enable the user to mechanically compare artificial intervertebral discs and do not purport to provide
performance standards for artificial intervertebral discs.
1.3 These test methods describe static and dynamic tests by specifying load types and specific methods of applying these loads.
These tests are designed to allow for the comparative evaluation of artificial intervertebral discs.
1.4 These test methods do not purport to address all clinically relevant failure modes for artificial intervertebral discs, some of
which will be device specific. For example, these test methods do not address the implant’s resistance to expulsion or implant wear
resistance under expected in vivo loads and motions. In addition, the biologic response to wear debris is not addressed in these test
methods.
1.5 Requirements are established for measuring displacements, determining the yield load or moment, and evaluating the
stiffness of artificial intervertebral discs.
1.6 Some artificial intervertebral discs may not be testable in all test configurations.
1.7 The values stated in SI units are to be regarded as the standard with the exception of angular measurements, which may be
reported in terms of either degrees or radians.
1.8 The use of this standard may involve the operation of potentially hazardous equipment. 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.
1.9 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 Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E466 Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials
E467 Practice for Verification of Constant Amplitude Dynamic Forces in an Axial Fatigue Testing System
E468 Practice for Presentation of Constant Amplitude Fatigue Test Results for Metallic Materials
E1823 Terminology Relating to Fatigue and Fracture Testing
These test methods are 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, 2011June 1, 2018. Published January 2012August 2018. Originally approved in 2005. Last previous edition approved in 20052011 as
F2346 – 05.F2346 – 05 (2011). DOI: 10.1520/F2346-05R11.10.1520/F2346-18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2346 − 18
FIG. 1 Intervertebral Height Diagram
F1582 Terminology Relating to Spinal Implants
F2077 Test Methods For Intervertebral Body Fusion Devices
3. Terminology
3.1 All definitions below supersede definitions contained within Terminologies E6, E1823, F1582, and Practices E466, E467.
3.2 Definitions:
3.2.1 artificial intervertebral disc—a synthetic structure that is permanently implanted in the disc space between two adjacent
vertebral bodies to provide spinal column support and allow intervertebral motion.
3.2.2 coordinate system/axes—three orthogonal axes are defined by Terminology F1582. The center of the coordinate system
is located at the geometric center of the artificial intervertebral disc. Alternative coordinate systems may be used with justification.
The XY-plane is to bisect the superior and inferior surfaces that are intended to simulate the adjacent vertebral end plates. The
positive Z-axis is to be directed perpendicular to the bisector of the disc space, oriented in the superior direction. The positive
X-axis is parallel to the intervertebral space, oriented in the anterior direction and the positive Y-axis is parallel to the disc space,
oriented in the left direction. Force components parallel to the XY-plane are shear components of loading. The compressive axial
force is defined to be the component in the negative Z direction. Torsional load is defined to be the component of moment parallel
to the Z-axis.
3.2.3 fatigue life—the number of cycles, N, that the artificial intervertebral disc can sustain at a particular load or moment before
functional failure occurs.
3.2.4 functional failure—permanent deformation that renders the artificial intervertebral disc ineffective or unable to adequately
resist load.
3.2.5 ideal insertion location—the location of the artificial disc in the intervertebral space that is suggested in the manufacturer’s
surgical installation instructions. The ideal insertion location is to be described with respect to the simulated inferior and superior
vertebral bodies (polyacetal or metal blocks) and will be dictated by the device design.
3.2.6 intended method of application—artificial intervertebral discs may contain different types of features to stabilize the
implant-tissue interface such as threads, spikes, and textured surfaces. Each type of feature has an intended method of application
or attachment to the spine.
3.2.7 intended spinal location—the anatomic region of the spine intended for the artificial intervertebral disc. Artificial
intervertebral discs may be designed and developed for specific regions of the spine such as the cervical, thoracic, and lumbar
spine. Also, since different surgical approaches may exist, the description of the intended spinal location should include both the
indicated spinal levels and the ideal insertion locations within the intervertebral space allowed at each level.
3.2.8 intervertebral height—the minimum distance parallel to the Z-axis in the YZ-plane between the unaltered simulated
3,4
vertebral bodies: minimum height of 2 mm and maximum height of 16.5 mm. See Fig. 1.
3.2.9 load point—the point through which the resultant force on the intervertebral device passes; that is, the geometric center
of the superior fixture’s sphere (see Figs. 2-4).
Nissan, M., Gilad, I., “The Cervical and Lumbar Vertebrae—An Anthropometric Model,” Engineering In Medicine, Vol 13, No. 3, 1984, pp. 111–114.
Lu, J., Ebraheim, N.A., Yang, H., Rollins, J., and Yeasting, R. A., “Anatomic Bases for Anterior Spinal Surgery: Surgical Anatomy of the Cervical Vertebral Body and
Disc Space,” Surg Radiol Anat, Vol 21, No. 4, 1999, pp. 235–239.
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FIG. 2 Compression Testing Configuration
3.2.10 maximum run-out load or moment—the maximum load or moment for a given test that can be applied to an artificial
intervertebral disc where all of the tested constructs have withstood 10 000 000 cycles without functional failure.
3.2.11 mechanical deterioration—deterioration that is visible to the naked eye and is associated with mechanical damage to the
device under test (for example, initiation of fatigue crack or surface wear).
3.2.12 offset angular displacement—(distance OB—Fig. 6) offset on the angular displacement axis equal to 2 % of the
intervertebral height, H, divided by the maximum radius of the implant in the XY-plane; for example, for an artificial intervertebral
disc with a height of 10 mm and a maximum radius in the XY-plane of 9 mm, distance OB = (0.02) (10 mm) / (9 mm) = 0.022
radians = 1.3°.
3.2.13 offset displacement—(distance OB—Fig. 6) offset on the linear displacement axis equal to 2 % of the intervertebral
height (for example, 0.2 mm for a 10 mm intervertebral height).
3.2.14 permanent deformation—the remaining linear or angular displacement (axial—mm, angular—degrees or radians)
relative to the initial unloaded condition of the artificial intervertebral disc after the applied load or moment has been removed.
3.2.15 stiffness (axial—n/mm, angular—n·mm/degree or n·mm/radian)—the slope of the initial linear portion of the
load-displacement curve or the slope of the initial linear portion of the moment-angular displacement curve. This is illustrated as
the slope of the line OG in Fig. 6. If the device does not exhibit a linear initial load/displacement curve, the displacement should
be reported at 30 %, 60 %, and 90 % of the yield load or moment.
3.2.16 test block—the component of the test apparatus for mounting the artificial intervertebral disc in the intended test
configuration.
3.2.17 ultimate displacement (axial—mm, angular—degrees or radians)—the linear or angular displacement associated with the
ultimate load or ultimate moment. This is illustrated as the displacement, OF, in Fig. 6.
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FIG. 3 Compression/Shear Testing Configuration
3.2.18 ultimate load or moment (axial—n, angular—n·mm)—the maximum applied load, F, or moment, M, transmitted by the
pushrod (assumed equal to force and moment component parallel to and indicated by load or torque cell) to the artificial
intervertebral disc assembly. This is illustrated as point E in Fig. 6.
3.2.19 yield displacement—the linear displacement (mm) or angular displacement (degrees or radians) when an artificial
intervertebral disc has a permanent deformation equal to the offset displacement or offset angular displacement. This is illustrated
as the distance OA in Fig. 6.
3.2.20 yield load or moment—the applied load, F, or moment, M, transmitted by the pushrod (assumed equal to force component
parallel to and indicated by load or torque cell) required to produce a permanent deformation equal to the offset displacement or
the offset angular displacement. This is illustrated as point D in Fig. 6.
4. Summary of Test Methods
4.1 These test methods are proposed for the mechanical testing of artificial intervertebral discs specific to the cervical, thoracic,
and lumbar spine.
4.2 All tests are to be performed on the prosthesis size with the smallest safety factor for the levels indicated for implantation.
If this worst-case size cannot be determined using theoretical or experimental methods such as simple stress calculations or finite
element analysis, then all available sizes are to be tested and the complete range of results are to be reported.
4.3 Fatigue testing of the artificial intervertebral discs will simulate a motion segment via a gap between two polyacetal test
blocks. The polyacetal will eliminate the effects of the variability of bone properties and morphology for the fatigue tests. The
minimum ultimate tensile strength of the polyacetal blocks shall be no less than 61 MPa.
4.4 Static testing of the artificial intervertebral discs will simulate a motion segment via a gap between two stainless steel blocks.
The minimum tensile yield strength of the blocks shall be no less than 1170 MPa.
4.5 The pushrod shall be manufactured from stainless steel having minimum tensile yield stress of 1170 MPa and be of
minimum cross-sectional area that would produce a compressive yield strength of at least 25 000 N.
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FIG. 4 Torsion Testing Configuration with a Pin-Slot Gimbal
FIG. 5 Polyacetal or Metal Test Block
4.6 Static and dynamic tests will evaluate the artificial intervertebral disc. The user of these test methods must decide which
series of tests are applicable to the artificial intervertebral disc in question. The user of these test methods may choose to use all
or a selection of the tests described in these test methods for testing a particular artificial intervertebral disc. For example, the
torsion test method may not apply to a device that has no mechanical resistance in axial rotation.
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FIG. 6 Typical Load Displacement Curve
5. Significance and Use
5.1 Artificial intervertebral discs are orthopaedic implants that replace degenerated natural intervertebral discs. Their function
is to support the anterior column of the spine while allowing motion at the operated level. These test methods outline materials
and methods for the characterization of the mechanical performance of different artificial intervertebral discs so that comparisons
can be made between different designs.
5.2 These test methods are designed to quantify the static and dynamic characteristics of different designs of artificial
intervertebral discs. These tests are conducted in vitro in order to allow for analysis of individual disc replacement devices and
comparison of the mechanical performance of multiple artificial intervertebral disc designs in a standard model.
5.3 The loads applied to the artificial intervertebral discs may differ from the complex loading seen in vivo, and therefore, the
results from these tests may not directly predict in vivo performance. The results, however, can be used to compare mechanical
performance of different artificial intervertebral discs.
5.4 Fatigue tests should be conducted in a 0.9 % saline environmental bath at 37°C at a rate of 2 Hz or less. Other test
environments such as a simulated body fluid, a saline drip or mist, distilled water, or other type of lubrication could also be used
with adequate justification. Likewise, alternative test frequencies may be used with adequate justification.
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5.5 It is well known that the failure of materials is dependent upon stress, test frequency, surface treatments, and environmental
factors. Therefore, when determining the effect of changing one of these parameters (for example, frequency, material, or
environment), all others should be kept constant to facilitate interpretation of the results. In particular, it may be necessary to assess
the influence of test frequency on device fracture while holding the test environment, implant materials and processing, and implant
geometry constant.
6. Apparatus
6.1 Test machines will conform to the requirements of Practices E4.
6.2 The intervertebral height, H, shall be determined from vertebral body and disc morphometric data at the intended level of
application. Suggested heights are as follows: 4 mm for the cervical spine, 6 mm for the thoracic spine, and 10 mm for the lumbar
spine. The intervertebral height should not reach zero prior to the onset of functional failure deterioration. If this occurs, the test
is considered a failure. The user of these test methods should select the intervertebral height that is appropriate for the device being
tested.
6.3 Axial Compression Test Apparatus:
6.3.1 The actuator of the testing machine is connected to the pushrod by a minimal friction ball-and-socket joint or universal
joint (that is, unconstrained in bending). The pushrod is connected to the superior fixture by a minimal friction sphere joint (that
is, unconstrained in bending and torsion). The hollow pushrod should be of minimal weight so as to be considered a “two force”
member.
6.3.2 It thus applies to the artificial intervertebral disc a resultant force directed along the pushrod’s axis and located at the center
of the superior fixture’s sphere joint (the geometric center of the device being tested).
6.3.3 For the fatigue tests, the device is placed between two polyacetal blocks, which are rigidly attached to the metal blocks
(Fig. 5).
6.3.4 For the static tests, metal blocks are to be used, which could be incorporated as an integral part of the superior and inferior
fixtures. The blocks are to have surfaces that mate geometrically with the intervertebral disc prosthesis similar to how the device
is intended to mate with vertebral end plates.
6.3.5 The test apparatus will be assembled such that the Z-axis of the intervertebral device is initially coincident with the
pushrod’s axis and collinear with the axis of the testing machine’s actuator and load cell.
6.3.6 The length of the pushrod between the center of the ball-and-socket joint to the center of the spherical surface is to be
a minimum of 380 mm. This is required to minimize deviation of the pushrod’s axis (direction of applied force, F) from that of
the test machine’s load cell axis. In other words, this is to minimize the error in using and reporting that the force indicated by
the load cell F is the applied load, F, and is
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