ASTM F2423-11(2016)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: F2423 − 11 (Reapproved 2016)
Standard Guide for
Functional, Kinematic, and Wear Assessment of Total Disc
Prostheses
This standard is issued under the fixed designation F2423; 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 of wear may occur and may have significant influence on the
functionality and performance of an articulating IVD
1.1 This guide provides guidance for wear and/or fatigue
prosthesis,andthereforetheusershouldconsidertheeffectsof
testing of total disc prostheses under functional and kinematic
other wear modes on the performance of the prosthesis.
conditions and, to this end, describes test methods for assess-
ment of the wear or functional characteristics, or both, of total 1.10 In order that the data be reproducible and comparable
disc prostheses. within and between laboratories, it is essential that uniform
procedures are established. This guide is intended to facilitate
1.2 Both lumbar and cervical prostheses are addressed.
uniformmethodsfortestingandreportingofdatafortotaldisc
1.3 Load and kinematic profiles for lumbar and cervical
replacement prostheses.
devices are not identical and, therefore, are addressed sepa-
1.11 Without a substantial clinical retrieval history of IVD
rately in the guide.
prostheses, actual loading profiles and patterns cannot be
1.4 Partial disc replacements, such as nucleus replacements
delineated at the time of the writing of this guide. It therefore
or facet joint replacements, are not intended to be addressed.
follows that the load and motion conditions specified by this
guide do not necessarily accurately reproduce those occurring
1.5 Wearisassessedusingaweightlossmethodinatesting
medium as defined in this guide. in vivo. Rather, this guide provides useful boundary/endpoint
conditions for evaluating prosthesis designs in a functional
1.6 This guide does not address any potential failure mode
manner.
as it relates to the fixation of the implant to its bony interfaces.
1.12 The values stated in SI units are to be regarded as the
1.7 It is the intent of this guide to enable comparison of
standard with the exception of angular measurements, which
intervertebral disc (IVD) prostheses with regard to wear and
may be reported in either degrees or radians.
fatigue characteristics when tested under the specified condi-
1.13 This guide is not intended to be a performance stan-
tions. It must be recognized, however, that there are many
possible variations in in vivo conditions. A single laboratory dard. It is the responsibility of the user of this guide to
characterizethesafetyandeffectivenessoftheprosthesisunder
simulation with a fixed set of parameters might not be
universally representative. evaluation.
1.14 This standard does not purport to address all of the
1.8 Most IVD prostheses primarily fall into two classifica-
safety concerns, if any, associated with its use. It is the
tions: articulating ball-in-socket type prostheses, and elasto-
responsibility of the user of this standard to establish appro-
meric or compliant type prostheses. For the former, this guide
priate safety and health practices and determine the applica-
primarilyaddressesMode1wear(definedherein);whereasfor
bility of regulatory limitations prior to use.
thelatter,thisguideaddressespotentialfailureoftheprosthesis
whentheimplantissubjectedtoarangeofmotionand/orloads
2. Referenced Documents
that fall within the full range of possible physiologic motions
and loads.
2.1 ASTM Standards:
F561 Practice for Retrieval and Analysis of Medical
1.9 For articulating components, this guide predominantly
Devices, and Associated Tissues and Fluids
describesaMode1test.Theuseriscautionedthatothermodes
F1582Terminology Relating to Spinal Implants
F1714GuideforGravimetricWearAssessmentofProsthetic
This guide is under the jurisdiction ofASTM 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 Dec. 1, 2016. Published December 2016. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2005. Last previous edition approved in 2011 as F2423–11. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/F2423-11R16. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2423 − 11 (2016)
Hip Designs in Simulator Devices 3.2.2.3 Y-axis, n—positive Y-axis is a global fixed axis
F1877Practice for Characterization of Particles relative to the test machine’s stationary base, and is directed
F2077TestMethodsForIntervertebralBodyFusionDevices laterally relative to the specimen’s initial unloaded position.
2.2 ISO Standard:
3.2.2.4 Z-axis, n—positive Z-axis is a global fixed axis
ISO 18192–1Implants for Surgery—Wear ofTotal Interver-
relative to the test machine’s stationary base, and is to be
tebral Spinal Disc Prostheses—Part 1: Loading and Dis-
directed superiorly relative to the specimen’s initial unloaded
placement Parameters for Wear Testing and Correspond-
position.
ing Environmental Conditions for Test
3.2.2.5 x-axis, n—positive x-axis is a fixed axis relative to
3. Terminology
the IVD prosthesis and a moving axis relative to the global
coordinate system, and is directed anteriorly relative to the
3.1 All functional and kinematic testing terminology is
prosthesis.
consistent with the referenced standards (for example, Test
Methods F2077, Terminology F1582, and so forth), unless
3.2.2.6 y-axis, n—positive y-axis is a fixed axis relative to
otherwise stated.
the IVD prosthesis and a moving axis relative to the global
coordinate system, and is directed laterally relative to the
3.2 Definitions:
prosthesis.
3.2.1 axial load, n—the resultant force F applied to the
axial
superior or inferior fixture-end plate that simulates the in vivo
3.2.2.7 z-axis, n—positive z-axis is a fixed axis relative to
load that an IVD prosthesis (original healthy disc) must resist.
the IVD prosthesis and a moving axis relative to the global
3.2.1.1 Discussion—Based on a healthy disc, the primary
coordinate system, and is directed superiorly relative to the
component would be an axial compressive force F in the
prosthesis.
Z
direction of the negative global Z axis, and it would pass
3.2.3 degradation, n—loss of material or function or mate-
through the origin of the IVD prosthesis. Shear components in
rial properties as a result of causes other than that associated
the XYplanewouldbe F and F .Lateralbendingmoment M
X Y X
with wear.
and flexion/extension moment M components would be cre-
Y
3.2.4 fluid absorption, n—fluid absorbed by the device
atedabouttheoriginwhentheaxialloaddoesnotpassthrough
material during testing.
it.
3.2.5 functional failure, n—permanent deformation or wear
3.2.2 coordinate system/axes, n—global XYZ orthogonal
that renders the IVD prosthesis assembly ineffective or unable
axesaredefinedfollowingaright-handedCartesiancoordinate
to resist load/motion or any secondary effects that result in a
system in which the XY plane is to bisect the sagittal plane
reduction of clinically relevant motions or the motions in-
angle between the superior and inferior surfaces that are
tended by the design of the device.
intended to simulate the adjacent vertebral end plates. The
global axes are stationary relative to the IVD prosthesis’s
3.2.6 interval net volumetric wear rate VR during cycle
i
inferior end plate fixture, which, in this guide, is also consid-
interval i (mm /million cycles), n—VR = WR/ρ, where ρ =
i i
ered to be stationary with respect to the test machine’s frame.
mass density (for example, units of g/mm ) of the wear
Lower case letters, xyz, denote a local, moving orthogonal
material.
coordinate system attached to the superior end plate fixture
3.2.7 interval net wear rate WR during cycle interval i
i
withdirectionsinitiallycoincidentwiththoseoftheglobalXYZ
(g/million cycles), n—WR =((NW – NW )/(number of cycles
i i i-1
axes, respectively. The 3-D motion of the superior relative to
in interval i))×10 .
the inferior end plate fixture is specified and is to be measured
3.2.7.1 Discussion—For i=1, NW =0.
i-1
in terms of sequential Eulerian angular rotations about the xyz
axes, respectively (z, axial rotation; x, lateral bending; and y, 3.2.8 intervertebral disc (IVD) prosthesis, n—nonbiologic
structure intended to restore the support and motion or a
flexion-extension).
portion thereof between adjacent vertebral bodies.
3.2.2.1 origin, n—center of the global coordinate system
which is located at the initial position of the total disc 3.2.9 kinematic profile, n—relativemotionbetweenadjacent
replacement’s instantaneous center of rotation (COR). vertebral bodies that the IVD prosthesis is subjected to while
3.2.2.1 Discussion—Some articulating devices do not have
being tested.
a single center of rotation, but instead have either a mobile
3.2.10 limit, n—a significant change in stiffness during a
center of rotation or multiple distinct centers of rotation,
given motion, indicating the implant has reached its designed
depending on the direction of movement. In this case, the
endpoint in range of motion.
origin should be explicitly defined by the user with a rationale
3.2.11 load profile, n—loading that the device experiences
for that definition.
while being tested under an applied kinematic profile or the
3.2.2.2 X-axis, n—positive X-axis is a global fixed axis
loading that the IVD prosthesis is subjected to if tested in load
relative to the test machine’s stationary base, and is to be
control.
directed anteriorly relative to the specimen’s initial unloaded
3.2.12 mechanical failure, n—failure associated with a de-
position.
fect in the material (for example, fatigue crack) or of the
bonding between materials that may or may not produce
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. functional failure.
F2423 − 11 (2016)
TABLE 1 Test Profiles and Associated Parameters for Cervical
3.2.13 Wear modes (1) for articulating type designs:
IVD Prostheses
3.2.13.1 Mode 1 refers to the articulation between two
Preferred Alternate
primary bearing surfaces only.
Axial
Displacement Control: Load Control:
Test Profile Load, N
3.2.13.2 Mode2occurswheneveraprimarysurfacearticu-
Range of Motion Applied Moment
(2-4)
A
lates directly against a secondary, nonbearing surface.
(ROM), degree (3) Ranges, Nm (3)
3.2.13.3 Mode 3 occurs when the two primary bearing Flexion/extension 100 ±7.5 ±2.0
Lateral bend/ 100 ±6 ±2.0
surfaces are still articulating together, but third-body particles
rotation ±6 ±4.0
have become entrapped between them.
A
TheuseroftheguidemustdeterminewhethertheROM(rangeofmotion)willbe
3.2.13.4 Mode4referstoanycontactandmotionoccurring
equally divided between flexion and extension or weighted more toward one of the
between two secondary, nonbearing surfaces.
motion directions.
3.2.14 net wear NW of wear specimen (g), n—NW 5 W
~
i i 0
2W !1~S 2S ! ; loss in weight of the wear specimen corrected
i i 0
for fluid absorption at end of cycle interval i.
joints, biconcave joints having a free-floating or semi-
3.2.15 net volumetric wear NV of wear specimen (mm ),
i constrained third body, metallic endplates bonded to elastomer
n—NV 5NW/ρ atendofcycleinterval iwhere ρ=massdensity
i i
cores, and single-axis hinge joints.
(for example, units of g/mm ) of the wear material.
5.2 Spinal Testing Apparatus:
3.2.16 run out (cycles), n—maximum number of cycles that
5.2.1 Test Chambers—Incaseofamulti-specimenmachine,
a test needs to be carried to if functional failure has not yet
each chamber shall be isolated to prevent cross-contamination
occurred.
of the test specimens. The chamber shall be made entirely of
3.2.17 wear, n—progressive loss of material from the de-
noncorrosive components, such as acrylic plastic or stainless
vice(s)asaresultofrelativemotionatthesurfacesasmeasured
steel, and shall be easily removable from the machine for
by the change in mass of the IVD prosthesis or components of
thorough cleaning between tests.
the IVD prosthesis. 5.2.2 Component Clamping/Fixturing—Since the purpose
3.2.17.1 Discussion—In the case of a nonarticulating, com-
of the test is to characterize the wear and/or fatigue properties
pliant IVD prosthesis, wear is defined simply as the loss of of the IVD prosthesis under functional and kinematic
material from the prosthesis. Note that inferior and superior
conditions, the method for mounting components in the test
bone interface components are excluded from this definition; chamber shall not compromise the accuracy of assessment of
see 5.2.2.
the weight loss or stiffness variation during the test. For
example, prostheses having complicated superior and inferior
3.2.18 weight S of soak control specimen (g), n—S initial
i 0
surfaces for contacting bone (for example, sintered beads,
and S at end of cycle interval i.
i
hydroxylapatite (HA) coating, plasma spray) may be specially
3.2.19 weight W of wear specimen (g), n—W initial and
i 0
manufactured to modify that surface in a manner that does not
W at end of cycle interval i.
i
affect the wear simulation.
5.2.3 The device should be securely (rigidly) attached at its
4. Significance and Use
bone-implant interface to the mating test fixtures.
4.1 This guide can be used to determine the fatigue and
5.2.4 The motion of the superior test fixture relative to the
wear behavior of IVD prostheses subjected to functional and
inferior testing fixture shall be unconstrained in three-
kinematiccyclicloading/motionforrelativelylargenumbersof
dimensional space except for the components in the direction
cycles(forexample,variousdesignsofIVDprostheses,aswell
of specified test motions/loads.
as the effects of materials, manufacturing techniques and other
5.2.5 Load and Motion (components in Table 1 and Table
design variables on one particular design can be determined
2):
using this guide).
5.2.5.1 An axial load is to be a compressive load applied in
4.2 This guide is intended to be applicable to IVD thedirectionofthenegative Z-axis.Deviationsfromthisasthe
IVD moves from its initial position are to be reported as shear
prostheses, that support load and transmit motion by means of
an articulating joint or by use of compliant materials. components F , F , and moments
...