ASTM F2624-12(2020)

Standard Test Method for Static, Dynamic, and Wear Assessment of Extra-Discal Single Level Spinal Constructs

ABSTRACT
This test method deals with static, dynamic, and wear testing of extra-discal motion preserving implants. These implants are intended to augment spinal stability without significant tissue removal while allowing motion of the functional spinal unit(s). Wear is assessed using a weight loss method and a dimensional analysis for determining wear of components used in extra-discal spinal motion preserving procedures, using testing medium as defined in this test method. This test method is not intended to address facet arthroplasty devices and any potential failure mode as it relates to the fixation of the device to its bony interfaces; and does not prescribe methods for assessing the mechanical characteristics of the device in translation. The static test includes the static flexion test, static extension test, static torsion test, static lateral bending test, and fatigue tests. Wear test includes flexion/extension wear assessment, rotational wear assessment, and bending wear assessment. The apparatus which shall be used includes implant components and spinal testing apparatus. The calculation and interpretation of wear results are also elaborated.
SIGNIFICANCE AND USE
4.1 This test method is designed to quantify the static and dynamic characteristics of different designs of single level spinal constructs. Wear may also be assessed for implants that allow motion using testing medium (see 6.1) for simulating the physiologic environment at 37 °C. Wear is assessed using a weight loss method in addition to dimensional analyses. Weight loss is determined after subjecting the implants to dynamic profiles specified in this test method. This information will allow the manufacturer or end user of the product to understand how the specific device in question performs under the test conditions prescribed in this test method.  
4.2 This test method is intended to be applicable for single level extra-discal spinal constructs. Three different types of fixtures are specified for testing single level extra-discal spinal constructs See Fig. 2, Fig. 4, and Fig. 5. See also Table 1.  
4.3 Implants may be designed using a variety of materials (for example, ceramics, metals, polymers, or combinations thereof), and it is the goal of this test method to enable a comparison of the static, dynamic, and wear properties generated by these devices, regardless of material and type of device.
SCOPE
1.1 This test method describes methods to assess the static and dynamic properties of single level spinal constructs.  
1.2 An option for assessing wear using a weight loss method and a dimensional analysis is given. This method, described herein, is used for the analysis of devices intended for motion preservation, using testing medium as defined in this standard (6.1).  
1.3 This test method is not intended to address any potential failure mode as it relates to the fixation of the device to its bony interfaces.  
1.4 It is the intent of this test method to enable single level extra-discal spinal constructs with regard to kinematic, functional, and wear characteristics when tested under the specified conditions.  
1.5 This test method is not intended to address facet arthroplasty devices.  
1.6 In order that the data be reproducible and comparable within and between laboratories, it is essential that uniform procedures be established. This test method is intended to facilitate uniform testing methods and data reporting.  
1.7 The motion profiles specified by this test method do not necessarily accurately reproduce those occurring in vivo. Rather this method provides useful boundary/endpoint conditions for evaluating implant designs in a functional manner.  
1.8 This test method is not intended to be a performance standard. It is the responsibility of the user of this test method to characterize the safety and effectiveness of the device under evaluation.  
1.9 Multiple test methods are included in this standard. However, it mu...

General Information

• Status: Published
• Publication Date: 30-Sep-2020
• 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

• Refers: ASTM F561-19 - Standard Practice for Retrieval and Analysis of Medical Devices, and Associated Tissues and Fluids
• Effective Date: 01-Jan-2019
• Refers: ASTM F1714-96(2018) - Standard Guide for Gravimetric Wear Assessment of Prosthetic Hip Designs in Simulator Devices
• Effective Date: 01-Apr-2018
• Refers: ASTM F1877-16 - Standard Practice for Characterization of Particles
• Effective Date: 01-Oct-2016
• Refers: ASTM F1717-15 - Standard Test Methods for Spinal Implant Constructs in a Vertebrectomy Model
• Effective Date: 01-May-2015
• Refers: ASTM F1717-14 - Standard Test Methods for Spinal Implant Constructs in a Vertebrectomy Model
• Effective Date: 01-Jan-2014
• Refers: ASTM F561-13 - Standard Practice for Retrieval and Analysis of Medical Devices, and Associated Tissues and Fluids
• Effective Date: 01-Sep-2013
• Refers: ASTM F1714-96(2013) - Standard Guide for Gravimetric Wear Assessment of Prosthetic Hip Designs in Simulator Devices
• Effective Date: 15-Mar-2013
• Refers: ASTM F1717-13 - Standard Test Methods for Spinal Implant Constructs in a Vertebrectomy Model
• Effective Date: 01-Feb-2013
• Refers: ASTM F1717-12a - Standard Test Methods for Spinal Implant Constructs in a Vertebrectomy Model
• Effective Date: 01-Dec-2012
• Refers: ASTM F1717-12 - Standard Test Methods for Spinal Implant Constructs in a Vertebrectomy Model
• Effective Date: 15-May-2012
• Refers: ASTM F2423-11 - Standard Guide for Functional, Kinematic, and Wear Assessment of Total Disc Prostheses
• Effective Date: 01-Jul-2011
• Refers: ASTM F1717-11a - Standard Test Methods for Spinal Implant Constructs in a Vertebrectomy Model
• Effective Date: 01-Jul-2011
• Refers: ASTM F1717-11 - Standard Test Methods for Spinal Implant Constructs in a Vertebrectomy Model
• Effective Date: 01-Jun-2011
• Refers: ASTM F561-05a(2010) - Standard Practice for Retrieval and Analysis of Medical Devices, and Associated Tissues and Fluids
• Effective Date: 01-Sep-2010
• Refers: ASTM F1717-10 - Standard Test Methods for Spinal Implant Constructs in a Vertebrectomy Model
• Effective Date: 01-Jul-2010

Overview

ASTM F2624-12(2020): Standard Test Method for Static, Dynamic, and Wear Assessment of Extra-Discal Single Level Spinal Constructs provides a comprehensive framework for evaluating the mechanical and wear performance of extra-discal motion-preserving spinal implants. Developed by ASTM International, this testing methodology addresses implants designed to stabilize spinal segments while preserving motion, without substantial tissue removal. The standard is applicable to single-level constructs but does not cover facet arthroplasty devices or fixation to bone interfaces.

Its primary objective is to ensure that manufacturers, researchers, and regulatory bodies have a standardized, reproducible method to assess device functionality under specified conditions. This improves the reliability, safety, and comparability of spinal implants in clinical and research settings.

Key Topics

• Static Testing: Methods include flexion, extension, torsion, and lateral bending assessments to determine stiffness, yield, and ultimate loads of the implants.
• Dynamic Testing: Involves repetitive loading (fatigue testing) to assess the endurance of the spinal construct under cyclic forces and moments, including flexion/extension, rotational, and lateral bending fatigue.
• Wear Assessment: Utilizes both weight loss and dimensional analysis after subjecting implants to motion profiles in a physiological testing medium. Provides insight into material loss over time.
• Fixture and Apparatus Design: Specifies the use of simulated vertebral body blocks, rotational test assemblies, and compression bending test configurations made from appropriate materials to accurately replicate test conditions.
• Testing Medium: Recommends physiological solutions at body temperature (37°C) for simulating in vivo conditions, especially for articulating surfaces.
• Data Reproducibility: Emphasizes standardization of procedures and reporting to ensure consistency across laboratories and test cycles.

Applications

Practical Value:

• Product Development: Provides medical device manufacturers with a robust protocol to evaluate the mechanical integrity and wear properties of new extra-discal spinal implants prior to clinical trials.
• Regulatory Submissions: Facilitates clear and standardized reporting of test results for regulatory bodies to assess device safety and performance.
• Comparative Assessment: Enables objective comparisons between different materials and implant designs, including ceramics, metals, polymers, and their combinations.
• Quality Assurance: Assists in routine batch testing for ongoing product quality and performance consistency.
• Research and Innovation: Supports academic and clinical research into the longevity, reliability, and biomechanical compatibility of motion-preserving spinal implants.

Target Audiences:

• Medical device manufacturers
• Regulatory agencies
• Clinical researchers and biomechanical engineers
• Quality control laboratories

Related Standards

To support comprehensive implant testing and evaluation, ASTM F2624-12(2020) references and can be used alongside several other important standards:

• ASTM E2309: Practices for Verification of Displacement Measuring Systems and Devices Used in Material Testing Machines
• ASTM F1714: Guide for Gravimetric Wear Assessment of Prosthetic Hip Designs in Simulator Devices
• ASTM F1717: Test Methods for Spinal Implant Constructs in a Vertebrectomy Model
• ASTM F1877: Practice for Characterization of Particles
• ASTM F2003: Practice for Accelerated Aging of Ultra-High Molecular Weight Polyethylene after Gamma Irradiation in Air
• ASTM F2423: Guide for Functional, Kinematic, and Wear Assessment of Total Disc Prostheses
• ASTM F561: Practice for Retrieval and Analysis of Medical Devices, and Associated Tissues and Fluids

These related standards help harmonize testing approaches across different types of orthopaedic implants and materials, ensuring best practices for biocompatibility, durability, and safety.

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Keywords: ASTM F2624-12, static testing, dynamic testing, wear assessment, extra-discal spinal implants, spinal construct fatigue, biomechanical testing, medical device standards, spinal implant evaluation, implant wear test

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: F2624 − 12 (Reapproved 2020)
Standard Test Method for
Static, Dynamic, and Wear Assessment of Extra-Discal
Single Level Spinal Constructs
This standard is issued under the fixed designation F2624; 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 device design. In most instances, only a subset of the herein
described test methods will be required.
1.1 This test method describes methods to assess the static
and dynamic properties of single level spinal constructs. 1.10 The values stated in SI units are to be regarded as the
standard with the exception of angular measurements, which
1.2 Anoptionforassessingwearusingaweightlossmethod
may be reported in either degrees or radians. No other units of
and a dimensional analysis is given. This method, described
measurement are included in this standard.
herein, is used for the analysis of devices intended for motion
1.11 This standard does not purport to address all of the
preservation, using testing medium as defined in this standard
safety concerns, if any, associated with its use. It is the
(6.1).
responsibility of the user of this standard to establish appro-
1.3 Thistestmethodisnotintendedtoaddressanypotential
priate safety, health, and environmental practices and deter-
failuremodeasitrelatestothefixationofthedevicetoitsbony
mine the applicability of regulatory limitations prior to use.
interfaces.
1.12 This international standard was developed in accor-
1.4 It is the intent of this test method to enable single level
dance with internationally recognized principles on standard-
extra-discal spinal constructs with regard to kinematic,
ization established in the Decision on Principles for the
functional, and wear characteristics when tested under the
Development of International Standards, Guides and Recom-
specified conditions.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.5 This test method is not intended to address facet
arthroplasty devices.
2. Referenced Documents
1.6 In order that the data be reproducible and comparable
2.1 ASTM Standards:
within and between laboratories, it is essential that uniform
E2309Practices forVerification of Displacement Measuring
procedures be established. This test method is intended to
Systems and Devices Used in Material Testing Machines
facilitate uniform testing methods and data reporting.
F561 Practice for Retrieval and Analysis of Medical
1.7 The motion profiles specified by this test method do not
Devices, and Associated Tissues and Fluids
necessarily accurately reproduce those occurring in vivo.
F1714GuideforGravimetricWearAssessmentofProsthetic
Rather this method provides useful boundary/endpoint condi-
Hip Designs in Simulator Devices
tions for evaluating implant designs in a functional manner.
F1717Test Methods for Spinal Implant Constructs in a
Vertebrectomy Model
1.8 This test method is not intended to be a performance
F1877Practice for Characterization of Particles
standard. It is the responsibility of the user of this test method
F2003Practice for Accelerated Aging of Ultra-High Mo-
to characterize the safety and effectiveness of the device under
lecular Weight Polyethylene after Gamma Irradiation in
evaluation.
Air
1.9 Multiple test methods are included in this standard.
F2423Guide for Functional, Kinematic, and Wear Assess-
However, it must be noted that the user is not obligated to test
ment of Total Disc Prostheses
using all of the described methods. Instead, the user should
only select test methods that are appropriate for a particular 3. Terminology
3.1 All terminology is consistent with the referenced
standards, unless otherwise stated.
ThistestmethodisunderthejurisdictionofASTMCommitteeF04onMedical
andSurgicalMaterialsandDevicesandisthedirectresponsibilityofSubcommittee
F04.25 on Spinal Devices. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2020. Published November 2020. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2007. Last previous edition approved in 2016 as F2624–12 (2016). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/F2624-12R20. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2624 − 12 (2020)
3.2 Definitions: 3.2.5.1 origin—the center of the coordinate system is lo-
3.2.1 center of rotation (COR)—the point about which the cated at the center of rotation of the testing fixture.
simulated vertebral bodies rotate in performing the range of
3.2.5.2 X-Axis—the positive X-Axis is a global fixed axis
motion (ROM) specified in this test method.
relative to the testing machine’s stationary base and is to be
3.2.2 compressive bending stiffness (N/mm)—the compres-
directed anteriorly relative to the specimen’s initial unloaded
sive bending yield force divided by elastic displacement (see position.
the initial slope of line BC in Fig. 1).
3.2.5.3 Y-Axis—the positive Y-Axis is a global fixed axis
3.2.3 compressive bending ultimate load (N)—the maxi- relative to the testing machine’s stationary base and is directed
mum compressive force in the X-Z plane applied to a spinal
laterally relative to the specimen’s initial unloaded position.
implant assembly (see the force at Point E in Fig. 1). The
3.2.5.4 Z-Axis—the positive Z-Axis is a global fixed axis
ultimate load should be a function of the device and not of the
relative to the testing machine’s stationary base and is to be
load cell or testing machine.
directed superiorly relative to the specimen’s initial unloaded
3.2.4 compressive bending yield load (N)—the compressive
position.
bending force in the X-Z plane necessary to produce a
3.2.6 degradation—loss of material, function, or material
permanent deformation equal to 0.020 times the active length
properties due to causes other than wear.
of the longitudinal element (see the force at Point D in Fig. 1).
3.2.7 elastic displacement (mm or degrees)—the displace-
3.2.5 coordinate system/axes—three orthogonal axes are
ment at 2% offset yield (see PointAin Fig. 1) minus the 2%
defined following a right-handed Cartesian coordinate system.
offset displacement (see Point B in Fig. 1). (The distance
The XY plane bisects the sagittal plane between the superior
between Point A and Point B in Fig. 1.)
and inferior surfaces that are intended to simulate the adjacent
3.2.8 fluid absorption—fluid absorbed by the device mate-
vertebral end plates. The positive Z axis is to be directed
rial during testing or while implanted in vivo.
superiorly.Forcecomponentsparalleltothe XYplaneareshear
components of loading.The compressive axial force is defined 3.2.9 functional failure—permanent deformation or wear
to be the component in the negative Z direction.Torsional load that renders the implant assembly ineffective or unable to
is defined to be the component of moment about the Z-axis. adequately resist load/motion or any secondary effects that
FIG. 1 Typical Force Displacement Curve
F2624 − 12 (2020)
result in a reduction of clinically relevant motions or the 3.2.20 stiffness (N/mm or N-m/degree)—the slope of the
motions intended by the design of the device. initial linear portion of the force-displacement or moment-
degree curve (the slope of Line OG in Fig. 1).
3.2.10 interval net volumetric wear rate—VR during cycle
i
3.2.21 test block—the component of the test apparatus for
interval i (mm /million cycles):
mounting a single level spinal construct for the intended test
WR
i
configuration (Fig. 3).
VR 5
i
ρ
3.2.22 torsional aspect ratio—the active length of the lon-
where:
gitudinal element divided by the distance from the center of
ρ = mass density (for example, units of g/mm ) of the wear
rotation to the insertion point of an anchor (for example: 0.78
material.
for a 35 mm active length, X=40mmand Y = 40/2 mm).
3.2.11 interval net wear rate—WR during cycle interval i 3.2.23 two percent (2 %) offset angular displacement
i
(degrees)—a permanent angular displacement in the X-Y plane
(mg/million cycles):
measured via the actuator equal to 0.020 times the torsional
NW 2 NW
~ !
i i21
WR 5 310 aspect ratio (for example: 0.9° for 0.78 × 0.02 × 180°/pi) (see
i
~# ofcyclesininterval i)
Point B in Fig. 1).
Note: for i=1, NW =0.
i–1
3.2.24 2 % offset displacement—a permanent deformation
3.2.12 kinematic profile—the relative motion between adja-
measuredviatheactuatorequalto0.020timestheactivelength
centvertebralbodiesthatthespinaldeviceissubjectedtowhile
ofthelongitudinalelement(forexample:1.04mmfora52mm
being tested (note that rigid devices may have minimal motion
active length) (see Distance OB in Fig. 1).
between vertebral bodies).
3.2.25 wear—the progressive loss of material from the
3.2.13 maximum run-out force or moment—the maximum
device(s)ordevicecomponentsasaresultofrelativemotionat
force or moment for a given test that can be applied to a single
the surface with another body as measured by the change in
level construct intended for fusion in which all of the tested
mass of the components of the implants. Or in the case of
constructs have withstood 5000000 cycles without functional
non-articulating, compliant components, wear is defined sim-
or mechanical failure. For non-fusion devices, the maximum
ply as the loss of material from the device. Note that bone
run-out force or moment is defined as 10000000 cycles
interface components of the device are excluded from this
without functional or mechanical failure.
definition. See 5.2.2, 5.2.4, and 5.2.5.
3.2.14 mechanical failure—failure associated with a defect
3.2.26 weight S of soak control specimen (g)—S initialand
i 0
in the material (for example, fatigue crack) or of the bonding
S at end of cycle interval i.
i
between materials that may or may not produce functional
3.2.27 weight W of wear specimen (g)—W initialand W at
i 0 i
failure.
end of cycle interval i.
3.2.15 net volumetric wear—NV of wear specimen (mm ):
i
3.2.28 ultimate displacement (mm or degrees)—the dis-
NW
placementassociatedwiththeultimateforce(displacementOF
i
NV 5
i
ρ
in Fig. 1).
at end of cycle interval i.
3.2.29 ultimate load (N or N-m)—the maximum applied
where: force, F, transmitted by the actuator that can be applied to the
spinal construct (Point E in Fig. 1).
ρ = mass density (for example, units of g/mm ) of the wear
material.
3.2.30 yield displacement—the displacement (mm or de-
grees) when a spinal construct has a permanent deformation
3.2.16 net wear—NW of wear specimen (g):
i
equal to the offset displacement (Distance OA in Fig. 1).
NW 5 ~W 2 W !1~S 2 S !
i 0 i i 0
3.2.31 yield force—the applied force, F, or moment trans-
Loss in weight of the wear specimen corrected for fluid ab-
mitted by the actuator required to produce a permanent
sorption at end of cycle interval i.
deformation equal to the offset displacement (Point D in Fig.
3.2.17 permanent deformation—the remaining displace-
1).
ment (mm) or angular rotation (degrees) relative to the initial
unloaded condition of the intervertebral body fusion device
4. Significance and Use
assembly after the applied force has been removed.
4.1 This test method is designed to quantify the static and
3.2.18 run-out (cycles)—the maximum number of cycles
dynamic characteristics of different designs of single level
thatatestneedstobecarriedtoiffunctionalfailurehasnotyet
spinal constructs. Wear may also be assessed for implants that
occurred.
allowmotionusingtestingmedium(see6.1)forsimulatingthe
3.2.19 single level spinal construct—a non-biologic physiologic environment at 37°C. Wear is assessed using a
structure, which lies entirely outside the intervertebral disc
weight loss method in addition to dimensional analyses.
space, intended to support the full or partial load between Weight loss is determined after subjecting the implants to
adjacent vertebral bodies. In this test method, this definition dynamicprofilesspecifiedinthistestmethod.Thisinformation
does not include facet arthroplasty devices. will allow the manufacturer or end user of the product to
F2624 − 12 (2020)
NOTE 1—This example depicts a 3D rendering of a possible method for implementing of the rotational testing apparatus. In this example, adjustment
mechanismsareemployedtoimpartbothaxialload(Fz)andaspondylolisthesisoffsetpriortolockingthespinalassemblyintheapparatus.Theactuator
isrotatedtoapplyflexion/extensionmoments.Spinalconstructsarealsotestedinlateralbendingandaxialtorsioninthissametestsetupwithappropriate
modifications.
FIG. 2 Rotational Testing Apparatus
understand how the specific device in question performs under 5.2.1 Test Chambers—In the case of a multi-specimen
the test conditions prescribed in this test method.
machine being used with testing medium, each chamber shall
be isolated to prevent cross-contamination of the test speci-
4.2 This test method is intended to be applicable for single
mens. The chamber shall be made entirely of non-corrosive
level extra-discal spinal constructs. Three different types of
components(suchasacrylicplasticorstainlesssteel)andshall
fixtures are specified for testing single level extra-discal spinal
be easy to remove from the machine for thorough cleaning
constructs See Fig. 2, Fig. 4, and Fig. 5. See also Table 1.
between tests.
4.3 Implants may be designed using a variety of materials
5.2.2 Forweartesting,thetestchamberalsomustisolatethe
(for example, ceramics, metals, polymers, or combinations
device/construct from wear centers created by the testing
thereof), and it is the goal of this test method to enable a
fixtures.
comparison of the static, dynamic, and wear properties gener-
5.2.3 The user must determine the appropriate degrees of
atedbythesedevices,regardlessofmaterialandtypeofdevice.
freedom for the device depending on its intended use (see
5. Apparatus
5.2.6).
5.2.4 Component Clamping/Fixturing—Since one of the
5.1 Implant Components—The device may comprise a va-
purposes may be to characterize the wear properties of the
riety of shapes and configurations. Some known forms include
spinal device, the method for mounting components in the test
screws which rigidly grip the vertebral bodies coupled with
flexible, elastic members; other forms may include rigid chamber shall not compromise the accuracy of assessment of
members coupled in a constrained (for example, pedicle the weight loss or stiffness variation during the test. For
screws) or semi-constrained manner (for example, screws and example, implants having complicated surfaces for contacting
rods connected with a universal joint with defined motion bone (for example, sintered beads, hydroxylapatite (HA)
limitations). Forms of these devices which employ hooks that
coating, plasma spray) may be specially manufactured to
engage posterior spinal elements are also envisioned; these
modify that surface in a manner that does not affect the wear
devices may support extension loading only or loads in both
simulation.
flexion and extension.
5.2.5 The device should be securely (rigidly) attached at its
5.2 Spinal Testing Apparatus: bone-implant interface to the test fixtures.
F2624 − 12 (2020)
NOTE 1—All dimensions are in mm.
FIG. 3 Simulated Vertebral Body Testing Block
FIG. 4 Schematic of Anterior/Posterior Shear Testing Apparatus
F2624 − 12 (2020)
FIG. 5 Schematic of Single Level Compression Bending Test
TABLE 1 Loading Modes and Associated Apparatus Listing
NOTE 1—304 stainless steel is used for the simulated spinous process
Possible Tests That May Be Conducted (see 1.9)
for rigidity purposes to enable the user to accurately characterize the
mechanical performance of the extra-discal implant.
NOTE 1—For all loading modes, static, dynamic, and wear tests are
described in this test method.
5.2.7.1 The simulated spinous process is only needed if the
implants are intended to be attached to the spinous process in
NOTE 2—“Offset” refers to 8 mm of offset induced in the spinal
construct (see Fig. 6) before subjecting the construct to rotational
vivo.
flexion/extension moments (see Fig. 2).
5.2.7.2 If a simulated spinous process is used, the entire
Associated Associated
Loading Mode
simulated vertebral body (Fig. 3) shall be made from stainless
Apparatus Figure
steel (minimum ultimate tensile strength of 500 MPa). Modi-
Rotational Fig. 2 Flexion
Extension fications(includingamaterialchange)tothetestingblocksare
Lateral Bending
allowed to conform to device design and the manufacturer’s
Axial Rotation
intended use of the extra-discal implant. Note that if wear
Fig. 2 and Fig. 6 Offset Flexion and Off-
between the implant and the spinous process is expected, the
set Extension
usershouldconsideralteringthesurfacefinishofthesimulated
spinous process to offer a more appropriate test model for
Shear Fig. 4 Anterior/Posterior
Shear
assessing the mechanical characteristics of the implant.
Compression Fig. 5 Compression Bending 5.2.8 Rotational Test Apparatus—The single level spinal
Bending
constructisassembledperthemanufacturer’sinstructions.The
spinal construct is placed in a fixture, which is capable of
inducing a rotational torque to test the single level construct
under flexion/extension, axial rotation, and lateral bending.
5.2.6 The construct mated with the testing fixture shall be
Fig. 2 depicts an example testing fixture for testing the spinal
constrained with the appropriate degrees of freedom for the
constructinflexion/extension.Notethattherepresentedtesting
intendeduse.Forexample,somedevicesmayonlybeintended
fixtures,whichattachtothesimulatedvertebralbodies(Fig.3)
toprovidestabilityinonemotion,whichwoulddictatethatthe
and the testing instrument, are for illustrative purposes only.
test fixture may be constrained in all other motions. Other
The user must design the appropriate fixtures for the device
devices, which provide stability along multiple degrees of
being tested and means by which they are rigidly fixed to the
freedom, would necessitate having more degrees of freedom
testing instrument. Note that the use of this fixture may
incorporated into the testing fixture. The user shall determine
produceshear(side)loadsontheactuator.Toaddresspotential
and justify the appropriate degrees of freedom of the test
adverse effects on the performance of the actuator and the
fixture.
readings of the load cell, the user may wish to restrict this side
5.2.7 Blocks are to be made from polyacetal homopolymer
load by blocking translation of the actuator or by using
(minimum ultimate tensile strength shall be no less than 61
appropriate bearings and/or joints to remove this side load.
MPa). It is suggested that the simulated spinous process be
5.2.9 Anterior-Posterior Shear Apparatus—Thesinglelevel
made from stainless steel (minimum ultimate tensile strength
spinal construct is assembled per the manufacturer’s instruc-
of 500 MPa). Other materials may also be used based on the
tions. One simulated vertebral body is rigidly connected to the
design intent of the implant being tested (for example, some
actuator of the testing instrument. The other simulated verte-
devices may depend on spinous process bone compliance to
bral body is constrained along the X-axis. Load, Fx, is applied
properly function, which would preclude using stainless steel
as the spinous process material.) along the X-axis as indicated in Fig. 4.
F2624 − 12 (2020)
5.2.10 Compression Bending Apparatus—The single level 5.2.12.5 Torsional loads/motions are generated by positive
spinal construct is assembled per the manufacturer’s instruc- and negative rotation about the Z-axis.
tions.Theinferiorvertebraisrigidlyattachedtothetestframe,
5.2.12.6 Anterior/posterior shear loads are applied in the
and the actuator is attached to the superior block to apply
direction of the positive and negative X-axis.
loads/displacements along the Z-axis (Fig. 5). For certain
5.2.12.7 Center of Rotation (COR)—See the Appendix
implants,itmaynotbedesirableforthesuperiorblocktorotate
(X1.7) for a discussion on the COR. Since the COR will vary
during testing. In this case, the rotation may be blocked,
accordingtodevicedesignandintendeduse,itisimpossibleto
thereby eliminating a degree of freedom in the test.To do this,
artificially specify the coordinates of the COR for testing.
place an aluminum block between the modified polyacetal
Therefore,theCORmustbedeterminedbytheenduserofthis
block and the superior fixture to stop rotation of the simulated
test method for the specific device being tested. The user
vertebral body and eliminate a degree of freedom. The total
should specify the COR based on the expected in-vivo COR.
clearance between a rigid block (for example, aluminum or
5.2.13 Frequency for Fatigue and Wear Tests:
stainless steel), a polyacetal block, and a base plate shall not
5.2.13.1 Test frequency shall be determined and justified by
exceed 0.10 mm. By blocking rotation, the test effectively
the user of this test method. For wear and dynamic testing, the
becomes an axial compression test. Note also that the inferior
testfrequencyfordeviceswithpolymericcomponentsshallnot
plate should be free to translate in the XY plane to avoid
exceed 2 Hz without adequate justification, ensuring that the
uncontrolled forces in the Fx direction.
applied motion (load) profiles remain within specified toler-
5.2.11 Simulated Spondylolisthesis Offset (for use in rota-
ances and that the frequency does not adversely affect deter-
tional testing apparatus—see Fig. 2 and Table 1). Induce an
mination of the construct’s wear and functional characteristics.
offset along the positive X-axis such that one vertebral body is
For devices with all metal components, the test frequency may
displaced 8 mm. This number represents the limit of a grade 1
be increased to 5 Hz. Other frequencies, with adequate
spondylolisthesis based on a 32 mm vertebral body dimension
justification, may be used during fatigue testing if an accurate
in the sagittal plane (Wolf, 2001 (1) and Chaynes, 2001 (2))
determinationoftheconstruct’spropertiesisnotcompromised.
relative to the other vertebral body and fix the spinal construct
The user is cautioned that care should therefore be taken to
in this configuration (Fig. 6). Attach the longitudinal member
select an appropriate test frequency as testing at too high a
to the simulated vertebral bodies and tighten fasteners accord-
frequency may adversely affect an accurate determination of
ing to the manufacturer’s instructions.
the construct’s properties.
5.2.12 Range of Motion (ROM):
5.2.14 Cycle Counter:
5.2.12.1 Axialcompressiveloads/motionsareappliedinthe
5.2.14.1 One complete motion is the entire range from
direction of the negative Z-axis.
starting position, through the range of motion and returning to
5.2.12.2 Flexion loads/motions are generated by positive
the starting position. Cycles are to be counted using an
rotation about the Y-axis.
automated counting device.
5.2.12.3 Extension loads/motions are generated by negative
rotation about the Y-axis.
6. Reagents and Materials
5.2.12.4 Lateral bend loads/motions are generated by posi-
tive and negative rotation about the X-axis. 6.1 Testing Medium:
6.1.1 Theuserhastheoptionoftestingthespinalimplantin
ambient conditions or in a testing medium, as determined by
The boldface numbers in parentheses refer to a list of references at the end of
this standard. the end user of the standard. If the devices are known to be
NOTE 1—Induce 8 mm offset in construct prior to attaching the longitudinal member.
FIG. 6 Schematic of Simulated Spondylolisthesis Offset for Flexion/Extension Test in Rotational Testing Apparatus
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temperature- and environment-dependent, testing shall be con- must be kept in a clean environment to avoid contamination.
ducted in a physiological solution at 37°C (see 6.1.3). The test assembly can be disassembled to facilitate examina-
6.1.2 If the device does not have articulating surfaces or tion of surface conditions.
surfaces that move relative to one another, the user may test at
7.3 Polymeric specimens may require pre-conditioning, as
ambient temperature in air or in a solution containing 0.9%
device stiffness may depend on temperature and/or hydration
saline.
of the polymer. In addition, the user may also wish to consider
6.1.3 Ifthedevicecontainsarticulatingsurfaces,orsurfaces
the effects of polymer aging on the mechanical properties of
that move relative to one another, the device shall be tested in
the device (the user should reference Practice F2003 for more
a testing medium containing bovine serum diluted to a protein
information).
concentration of 20 g/L in deionized water. The user should
reference Guide F2423 for more information on the use of
8. Preparation of Apparatus
serum in the testing medium.
8.1 The functional surface of the implantable form of the
6.1.4 To retard bacterial degradation, freeze and store the
devicetobetestedshallbeproducedusingamethodequivalent
serum until needed for testing. In addition, the testing medium
tothatusedfortheimplantableformoftheconstruct,including
shouldcontain0.2%sodiumazide(orothersuitableantibiotic/
sterilization.
antimycotic) to prevent the growth of microorganisms (fungi,
yeast, bacteria, and so forth) that can degrade the lubricating 8.2 It is permissible to exclude non-functional features that
may interfere with obtaining wear/functional measurements.
properties of the serum, and can contaminate samples of wear
particles that are subsequently isolated from the serum. Other For example, bone implant interfaces such as HA, plasma-
spray titanium, and beads may be omitted since they may
lubricantsshouldbeevaluatedtodetermineappropriatestorage
conditions.Itisrecommendedthatethylene-diaminetetraacetic abrade the fixtures and thus produce an unwanted mixture of
functional and not-functional component wear particles (see
acid (EDTA) be added to the testing medium containing serum
at a concentration of 20 mM to bind calcium in solution and 5.2.2).
minimize precipitation of calcium phosphate onto the bearing
8.3 The requirements of Guide F1714, Section 5 on “Speci-
surfaces.The latter event has been shown to strongly affect the
men Preparation” shall be followed.
friction and wear properties, particularly of polyethylene/
ceramic combinations. The addition of EDTA to other testing
9. Procedure
mediums should be evaluated.
9.1 Not all devices are designed to resist loading in all
6.1.5 The bulk temperature of the testing medium shall be
motions specified in this test method. The user must therefore
maintained at 37 63°C unless otherwise specified.
determinewhichmotionprofilesandtestsareappropriatefora
6.1.6 The user is cautioned that internal heating of the
given device (see Table 1).
implant may cause localized temperatures to fall outside the
9.2 Angularmotionsshallbecontrolledwithanaccuracyof
37 63°C of the testing medium. Internal local temperatures
60.5°,andloadsshallbecontrolledwithanaccuracyof 65%
may depend on a number of factors including, but not limited
of the maximum load.
to, joint friction, material hysteresis, conductivity of the
device-fixture materials, design, and test frequency. Localized
9.3 Mount the spinal device to the polyacetal homopolymer
elevatedtemperaturesmayhaveaneffectonthemechanicalas
blocks (Fig. 2). Install the anchors according to the manufac-
well as the wear properties of the implant. If the device
turer’sinstructionswiththefollowingstipulation:anchorsshall
experiences localized elevated temperatures, the user must
be inserted into the blocks in a manner that prevents the
describe the effect the selected frequency and resultant local-
impingement of any potentially pivoting or rotating features of
ized temperature have on the test results, or justify that the
the anchor against the test block. This may be achieved by
effects are physiologically relevant. Refer to Section X1.5 for
inserting the anchor such that, at full angulation of any of the
further information.
potentially pivoting or rotating features, clearance with respect
to the test block is always maintained. Note that modifications
7. Sampling Test Specimens
to the blocks may be required to adapt the test blocks to the
spinal device.
7.1 It is suggested that a minimum sample size of five be
used for the static tests and a minimum of two to be used for
9.4 The distance between the simulated endplates of the
each load or motion in the wear testing of the device. For
vertebral bodies shall be 20 mm (that is, simulated disc space
fatigue testing, it is recommended that the user develop a
height) in the final assembled configuration. Other distances
load-cycle curve with at least six data points, with an evalua-
may be appropriate if justified.
tion of two samples demonstrating the maximum run out load.
NOTE 2—Assuming a normal distribution of anterior disc space heights
However, it should be noted that, as for any experimental
in the population, 20 mm is within three standard deviations of the mean
comparison,thetotalnumberofneededspecimenswilldepend
and represents an upper limit for anterior intervertebral disc space heights
on the magnitude of the difference to be established, the
of the reported L4-L5 and L5-S1 intervertebral disc space heights (3, 4).
repeatabilityoftheresults(standarddeviation),andthelevelof
9.4.1 Rotational Testing Apparatus—In order to account for
statistical significance desired.
theaxialpreloadthedevicewouldbesubjectedto in vivointhe
7.2 The test assemblies (that is, spinal components in the neutral position, the test blocks/fixture shall be designed such
tested configuration) shall be labeled so they can be traced and that the implant, for static, fatigue, and wear testing, is
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subjected to a nominal axial load of 300 N (Fz) when the extension bending stiffness (N-m/degree). If the device does
implants are in the neutral position at the start of the test. See not have linear elastic characteristics, record only the ultimate
Note3.Thetorqueimpartedtotheimplantsshallbemonitored displacement (degrees) and ultimate load (N-m). If the blocks
and tared to zero prior to commencement of the rotational test. meet prior to failure of the device, the displacement value and
If the implant has viscoelastic characteristics, this nominal load value at this point shall be used for the extension bending
axial load may change significantly throughout the test. If a ultimate displacement (degrees) and extension bending ulti-
significant change in this axial load is expected during the test, mate moment (N-m).
the user should characterize the load response to the axial 9.5.3 Static Axial Rotation Test:
preload as a function of time. A load cell may be mounted
9.5.3.1 Install the spinal construct in the rotational testing
along the Z-axis to characterize the axial load throughout the apparatus as indicated in Section 5 such that the actuator
duration of the test. Note that this is only possible for devices
rotation generates axial rotation about the Z-axis.
thatcanresistcompressiveforces.Theusermustdeterminethe 9.5.3.2 Load the test apparatus at a maximum rate up to
appropriate methodology to exert this axial preload on the
60°/min.
device.As an example, the user may design a Z-direction axial
9.5.3.3 Record the torque-angular displacement curves. For
offset for the position of the axis of rotation such that the
devices, which exhibit linear elastic behavior, determine the
device, in its final assembled form, is being compressively
angular displacement (degrees) at 2% offset displacement,
loadedwith300N(seeFig.2foranexamplefixture).Loading
elasticangulardisplacement(degrees),yieldtorque(N-m),and
with a dead weight in the Fz direction is also a possible
torsional stiffness (N-m/degree). For devices, which do not
alternative. Other preloads may be appropriate with proper
exhibit linear elastic behavior, simply record the torque at 10º
justification.Forexample,certaindevicesmaybeassembled in
rotation.
vivo with tensile preload forces; in this case, the application of
NOTE 4—If the device is symmetric about the X-Z and Y-Z planes
appropriate tensile forces on the device in the final assembled
bisecting the device, only left or right rotation need to be conducted.
form on the test blocks would be necessary.
9.5.4 Static Lateral Bending Test:
NOTE 3—Note the rationale for a 300 N axial load. Assuming an
9.5.4.1 Install the spinal construct in the rotational testing
approximate 1000 N load (based on intradiscal pressure measurements
apparatus as indicated in Section 5 such that the actuator
made by A. Nachemson, 1966, 1981) axially on the spinal column, one
rotation generates axial rotation about the X-axis.
can equally assume that approximately ⁄3 of this load is resisted by the
posteriorelements,yieldingapproximately300Nofload,whichwouldbe 9.5.4.2 Load the test apparatus with a moment (6 X-Axis
applied to the extra-discal elements described in this test method.
rotation) at a rate up to a maximum of 60°/min.
9.5 ProcedureforStaticRotationalTests—Evaluateonlythe
NOTE 5—If the device is symmetric about the X-Z plane bisecting the
load parameters in the relevant direction.
device, only left or right lateral bending need be conducted.
9.5.1 Static Flexion Test:
9.5.4.3 If the device has linear elastic characteristics, estab-
9.5.1.1 Install the spinal construct in the rotational testing
lish the displacement (degrees) at 2% offset displacement,
apparatus as indicated in Section 5 such that the actuator
elasticangulardisplacement(degrees),extensionbendingyield
rotation generates flexion rotation about the Y-axis.
force (N-m), and extension bending stiffness (N-m/degree). If
9.5.1.2 Load the test apparatus with a moment (+Y rotation)
the device does not have linear elastic characteristics, record
at a rate up to a maximum of 60°/min.
only the ultimate displacement (degrees) and ultimate load
9.5.1.3 Record the load displacement curves. If the device
(N-m). Note that if the blocks meet prior to failure of the
has linear elastic characteristics, establish the ultimate dis-
device, the displacement value and load value at this point are
placement (degrees) at 2% offset yield, elastic angular dis-
to be used for the extension bending ultimate displacement
placement (degrees), flexion bending yield load (N-m), and
(degrees) and extension bending ultimate moment (N-m).
flexion bending stiffness (N-m/degree). If the device does not
9.6 Procedure for Dynamic Rotational Tests—Evaluateonly
have linear elastic characteristics, record only the flexion
the load parameters in the relevant direction. For all fatigue
bending ultimate displacement (degrees) and flexion bending
tests, this test method prescribes testing in load control, if
ultimate load (N-m). Note that if the blocks meet prior to
possible.
failure of the device, the displacement value and force value at
this displacement are to be used for the flexion bending 9.6.1 Add testing medium to the tank (6.1) if required.
9.6.2 Flexion/Extension Fatigue—Apply a sinusoidal mo-
ultimate displacement (degrees) and flexion bending ultimate
load (N-m). ment (6Y-Axis rotation) to the spinal construct. The loading
should be maintained via a constant sinusoidal load amplitude
9.5.2 Static Extension Test:
9.5.2.1 Install the spinal construct in the rotational testing control. A constant load ratio (R) for all tests should be
established. If testing in displacement control, displacements
apparatus as indicated in Section 5 such that the actuator
rotation generates extension rotation about the Y-axis. shall be maintained via constant sinusoidal displacement am-
plitude control. The end of the test occurs when the spinal
9.5.2.2 Load the test apparatus with a moment (-Y rotation)
at a rate up to a maximum of 60°/min. construct has a failure or reaches runout.
9.5.2.3 Record the load displacement curves. If the device 9.6.3 Note that one specific load ratio cannot be standard-
has linear elastic characteristics, establish the displacement ized due to different intended uses of these types of spinal
(degrees) at 2% offset displacement, elastic angular displace- implants. For example, some devices are intended to resist
ment (degrees), extension bending yield force (N-m), and extension loads while others may be equally balanced in
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limiting flexion and extension loading. In this example, differ- compressive bending yield load (N), compressive bending
ent R ratios would be required to properly assess the function stiffness (N/mm), compressive bending ultimate displacement
ofthespinalimplant.Itisthereforeincumbentupontheuserto (mm) and compressive bending ultimate load (N).
select and justify an appropriate R ratio or displacement end
9.12 Procedure for Dynamic Compression Bending Testing:
limits.
9.12.1 Apply force, Fz via a sinusoidal waveform as de-
9.6.4 AxialRotationalFatigue—Applyasinusoidalmoment
scribedinSection5ofthistestmethodunderloadcontrol.The
load(6Z-Axisrotation)tothespinalconstruct.Aconstantload
user of this test method should select the necessary forces to
ratio of –1 shall be used. If testing in displacement control,
developawelldefinedforce-cycletofailuretrendcomprisedof
displacements shall be maintained via constant sinusoidal
a minimum of six data points. Suggested maximum forces for
displacement amplitude control divided equally between left
initial dynamic tests are 25, 50, and 75% of the ultimate static
and right axial rotation.
force.Asemi-log fatigue graph of maximum applied force, F,
9.6.5 Lateral Bending Fatigue—Applyasinusoidalmoment
versus the number of cycles to failure shall be plotted.
load (6X-Axis rotation) to the spinal construct. The loading
Alternatively, the user may apply Fz via a sinusoidal wave
should be maintained via a constant sinusoidal load amplitude
form under displacement control. The user of this test method
control. A constant load ratio (R) for all tests should be
should select the necessary displacements to develop a well
established. For devices that are symmetric about the X-Z
defined displacement-cycle curve comprised of a minimum of
plane, a constant load ratio of –1 shall be used. If testing in
six data points. The end of this test is defined as functional
displacement control, displacements shall be maintained via
failure of the construct or the ability to reach runout without
constant sinusoidal displacement amplitude control. For de-
functional failure. However, any mechanical failure should be
vices that are symmetric, rotation shall be equal in left and
noted at the runout cycle point (for example, crack initiation
right lateral bending. Other displacements may be justified,
and crack propagation). The maximum run-out force or dis-
dependingondesignandintendedfunctionoftheimplant.The
placement shall be determined. The precision in establishing
endofthetestoccurswhenthespinalconstructhasafailureor
themaximumrunoutforceshouldnotdeviatemorethan10%
reaches runout.
of the static ultimate strength of the single-level spinal con-
9.7 Evaluate at least six specimens to generate a load-cycle
struct.
or displacement-cycle curve. Establish the maximum runout
9.13 The creep behavior (or stress relaxation behavior if
load or displacement. Suggested maximum forces for initial
testing under displacement control) of the implant shall be
dynamic tests are 25, 50, and 75% of the ultimate static force.
documented by noting the maximum displacement reached as
Continuefatiguetestingspecimensuntilthedifferencebetween
a function of cycle count.
aloadinwhichaconstructhasfailedandthemaximumrunout
loadisnogreaterthan10%oftheultimateloadfromthestatic
9.14 If a device ceases to function, the test shall be
tests. For example, if the flexion bending ultimate load of the
terminated. The mechanism of failure and number of cycles at
implant is 16 N-m and the user demonstrates runout at 3 N-m,
which the functional failure occurred, or was discovered, shall
the 3 N-m is to be considered a run-out value only if the user
be noted.
demonstrates failure of the device below the run out cycle
9.14.1 During dynamic tests, observations of any mechani-
count at a value between 3 and 4.6 N-m. A semi-log fatigue
cal failures (for example, cracks) shall be documented with a
curve of the load versus number of cycles at failure shall be
complete description of the mechanical failure, number of
plotted.
cyclesattheinitialobservationandsubsequentchanges,ifany,
9.8 The creep behavior of the implant shall be documented in mechanical behavior of the construct. It is recommended
by noting the maximum angle reached as a function of cycle that implants be examined for mechanical failure at intervals
throughout the dynamic tests. If a crack or other mechanical
count. If testing in displacement control, the stress relaxation
behavior of the implant shall be documented by noting the failure is found, the crack location and cycle count along with
the size and description at which it was discovered shall be
maximum load reached as a function of cycle count.
recorded.Attheengineeringjudgmentoftheuser,thetestmay
9.9 Ifadeviceceasestofunction,thetestisterminated.The
be continued following the observation of a mechanical failure
mechanism of failure and number of cycles at which the
to evaluate the ability of the implant to function under the
functional failure occurred, or was discovered, shall be noted.
applied forces. If a mechanical failure is detected following a
9.10 Note the initial and secondary failures, modes of
runout,thefailure(thatis,location,size,anddescription)atthe
failure, and deformations of components prior to removing the
last cycle count without any detectable cracks shall be re-
spinal construct from the test apparatus. Evaluate all surface
corded. For example, if an implant reached runout and a crack
changes.
was discovered on the implant upon removal, this crack shall
be adequately described, noted, and assigned the previous
9.11 Procedure for Static Compression Bending Testing:
examination cycle count (for example, 4000000 cycles)
9.11.1 Apply force, –Fz, as described in Section 5 of this
before a 5000000 cycle runout was attained. Functionally,
test method under position control at a rate of no greater than
however, this implant would still be considered a runout.
25 mm/minute until functional or mechanical failure of the
spinal construct occurs. 9.14.2 If testing under load control, an R value ≥10 (R =
9.11.2 Record the load displacement curves. Establish the Minload/Maxload)shallbeusedforthecompressionbending
2% offset displacement (mm), elastic displacement (mm), tests.Unlessotherwisejustifiedbyintendeduseandtheservice
F2624 − 12 (2020)
life expectancy of the device, for devices intended for non- was discovered on the implant upon removal, this crack shall
fusion (that is, to preserve motion), all tests should be be adequately described and noted and assigned the previous
conducted to a runout of 10000000 cycles, and 5000000 examination cycle count (for example, 4000000 cycles)
cycles for devices intended for fusion (that is, to inhibit before a 5000000 cycle runout was reached. Functionally,
motion) (See Rationale Section, Appendix X1). however, this implant would still be considered a runout.
9.18.2 An R value of –1 shall be used for the anterior/
9.15 Procedure for Static Anterior/Posterior Shear Testing:
posteriorsheartests.Unlessotherwisejustifiedbyintendeduse
9.15.1 Applyforce,+Fxand/or–Fx,asdescribedinSection
and service life expectancy of the device, for devices intended
5 of this test method under position control at a rate no greater
topreservemotion,alltestsshouldbeconductedtoarunoutof
than 25 mm/minute until functional or mechanical failure of
10000000 cycles, and 5000000 cycles for devices intended
the spinal construct occurs.
to inhibit motion (see Rationale Section, Appendix X1).
9.15.2 Th
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