ASTM F2789-10(2015)
(Guide)Standard Guide for Mechanical and Functional Characterization of Nucleus Devices
Standard Guide for Mechanical and Functional Characterization of Nucleus Devices
SIGNIFICANCE AND USE
5.1 Nucleus devices are generally designed to augment the mechanical function of native degenerated nucleus material or to replace tissue that has been removed during a surgical procedure. This guide outlines methods for evaluating many different types of devices. Comparisons between devices must be made cautiously and with careful analysis, taking into account the effects that design and functional differences can have on the testing configurations and overall performance, and the possibility that mechanical failure may not be related to clinical failure and inversely, that mechanical success may not be related to clinical success.
5.2 These tests are conducted in vitro to allow for analysis of the mechanical performance of the nucleus device under specific testing modalities. The loads applied may differ from the complex loading seen in vivo, and therefore the results from these tests may not directly predict in vivo performance.
5.3 These tests are used to quantify the static and dynamic properties and performance of different implant designs. The mechanical tests are conducted in vitro using simplified loads and moments. Fatigue testing in a simulated body fluid or saline may have fretting, aging, corroding, or lubricating effects on the device and thereby affect the relative performance of tested devices. Hence, the test environment and the effect of that environment, whether a simulated body fluid, normal saline bath (9 g NaCl per 1000 mL H2O), or dry, is an important characteristic of the test and must be reported accurately.
5.4 Dynamic testing methods should be designed to answer the following questions, including but not limited to: Does the device still function as intended after cycling? Does it retain adequate performance characteristics (for example, mechanical and kinematic properties such as ROM)? Did the device wear or degrade? If there is evidence of wear or degradation of the device, it should be identified and quantified with reasonable ...
SCOPE
1.1 This guide describes various forms of nucleus replacement and nucleus augmentation devices. It further outlines the types of testing that are recommended in evaluating the performance of these devices.
1.2 Biocompatibility of the materials used in a nucleus replacement device is not addressed in this guide. However, users should investigate the biocompatibility of their device separately (see X1.1).
1.3 While it is understood that expulsion and endplate fractures represent documented clinical failures, this guide does not specifically address them, although some of the factors that relate to expulsion have been included (see X1.3).
1.4 Multiple tests are described in this guide; however, the user need not use them all. It is the responsibility of the user of this guide to determine which tests are appropriate for the devices being tested and their potential application. Some tests may not be applicable for all types of devices. Moreover, some nucleus devices may not be stable in all test configurations. However, this does not necessarily mean that the test methods described are unsuitable.
1.5 The science of nucleus device design is still very young and includes technology that is changing more quickly than this guide can be modified. Therefore, the user must carefully consider the applicability of this guide to the user’s particular device; the guide may not be appropriate for every device. For example, at the time of publication, this guide does not address the nucleus replacement and nucleus augmentation devices that are designed to be partially or completely resorbable in the body. However, some of the test recommended in this guide may be applicable to evaluate such devices. It has not been demonstrated that mechanical failure of nucleus devices is related to adverse clinical results. Therefore this standard should be used with care in evaluating proposed nucleus devices.
1.6 This guide is not int...
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Designation: F2789 − 10 (Reapproved 2015)
Standard Guide for
Mechanical and Functional Characterization of Nucleus
Devices
This standard is issued under the fixed designation F2789; 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 1.6 Thisguideisnotintendedtobeaperformancestandard.
It is the responsibility of the user of this guide to characterize
1.1 This guide describes various forms of nucleus replace-
the safety and effectiveness of the nucleus device under
ment and nucleus augmentation devices. It further outlines the
evaluation.
types of testing that are recommended in evaluating the
performance of these devices. 1.7 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
1.2 Biocompatibility of the materials used in a nucleus
standard. Angular measurements may be reported in either
replacement device is not addressed in this guide. However,
degrees or radians.
users should investigate the biocompatibility of their device
separately (see X1.1). 1.8 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.3 While it is understood that expulsion and endplate
responsibility of the user of this standard to establish appro-
fractures represent documented clinical failures, this guide
priate safety and health practices and determine the applica-
does not specifically address them, although some of the
bility of regulatory limitations prior to use.
factors that relate to expulsion have been included (see X1.3).
1.4 Multiple tests are described in this guide; however, the
2. Referenced Documents
userneednotusethemall.Itistheresponsibilityoftheuserof
2.1 ASTM Standards:
this guide to determine which tests are appropriate for the
D2990Test Methods forTensile, Compressive, and Flexural
devices being tested and their potential application. Some tests
Creep and Creep-Rupture of Plastics
maynotbeapplicableforalltypesofdevices.Moreover,some
D6204Test Method for Rubber—Measurement of Unvulca-
nucleus devices may not be stable in all test configurations.
nized Rheological Properties Using Rotorless Shear Rhe-
However, this does not necessarily mean that the test methods
ometers
described are unsuitable.
E6Terminology Relating to Methods of MechanicalTesting
1.5 The science of nucleus device design is still very young
E111Test Method for Young’s Modulus, Tangent Modulus,
and includes technology that is changing more quickly than
and Chord Modulus
this guide can be modified. Therefore, the user must carefully
E132TestMethodforPoisson’sRatioatRoomTemperature
consider the applicability of this guide to the user’s particular
E328Test Methods for Stress Relaxation for Materials and
device; the guide may not be appropriate for every device. For
Structures
example,atthetimeofpublication,thisguidedoesnotaddress
E1823TerminologyRelatingtoFatigueandFractureTesting
thenucleusreplacementandnucleusaugmentationdevicesthat
F561 Practice for Retrieval and Analysis of Medical
are designed to be partially or completely resorbable in the
Devices, and Associated Tissues and Fluids
body. However, some of the test recommended in this guide
F1582Terminology Relating to Spinal Implants
may be applicable to evaluate such devices. It has not been
F1714GuideforGravimetricWearAssessmentofProsthetic
demonstrated that mechanical failure of nucleus devices is
Hip Designs in Simulator Devices
related to adverse clinical results. Therefore this standard
F1877Practice for Characterization of Particles
should be used with care in evaluating proposed nucleus
F1980Guide for Accelerated Aging of Sterile Barrier Sys-
devices.
tems for Medical Devices
F2267TestMethodforMeasuringLoadInducedSubsidence
ThistestmethodisunderthejurisdictionofASTMCommitteeF04onMedical
andSurgicalMaterialsandDevicesandisthedirectresponsibilityofSubcommittee
F04.25 on Spinal Devices. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
CurrenteditionapprovedMay1,2015.PublishedJuly2015.Originallyapproved contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
in 2010. Last previous edition approved in 2010 as F2789 – 10. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
F2789-10R15. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2789 − 10 (2015)
of Intervertebral Body Fusion Device Under Static Axial 3.2.5 fatigue life, n—The number of cycles, N, that the
Compression nucleus device can sustain at a particular load or moment
F2346Test Methods for Static and Dynamic Characteriza- before functional or mechanical failure occurs.
tion of Spinal Artificial Discs
3.2.6 functional failure, n—A failure that renders the
F2423Guide for Functional, Kinematic, and Wear Assess-
nucleusdeviceineffectiveorunabletoresistloadorfunctionas
ment of Total Disc Prostheses
predetermined within desired parameters (for example, perma-
2.2 Other Standards:
nent deformation, dissociation, dehydration, expulsion, extru-
ISO 10993Biological Evaluation of Medical Devices: Parts
sion or fracture), or both.
1–20
3.2.6.1 Discussion—Functional failure may or may not be
ISO 18192–1Implants for Surgery—Wear ofTotal Interver-
correlated with clinical failure.
tebral Spinal Disc Prostheses
3.2.7 hysteresis, n—The resultant loop on a force displace-
ment plot that is created from a mechanical test performed on
3. Terminology
a viscoelastic material.The area inside the loop can be used to
3.1 For definition of terms, refer to Terminologies E6,
determine the energy absorption.
E1823, and F1582.
3.2.8 mechanical failure, n—A failure associated with the
3.2 Definitions:
onset of a defect in the material (for example, a fatigue
3.2.1 coordinate system/axes, n—Three orthogonal axes are
fracture, a static fracture, or surface wear).
defined by Terminology F1582. The center of the coordinate
3.2.8.1 Discussion—Amechanicalfailurecanoccurwithout
system is located at the geometric center of the native disc.
there being a functional failure.
Because of design intent, or procedural limitations, the device
3.2.9 migration, n—A condition during testing when a
might not be implanted at the center of the native disc;
device displaces from its original position during testing.
therefore, the geometric center of the disc might not be the
Migration may or may not be considered a specific type of
geometric center of the device. For uniformity in comparison
functional failure. The user is expected to define their criteria
between devices, it is important that the origin be placed with
for acceptable levels of migration and provide rationale for
respect to the disc, not the device. This is done so that all
thosecriteria.Seealsodefinitionsforexpulsion,extrusion,and
loading is consistently applied and measurement made with
subsidence.
respect to the anatomy of the spine, and not with respect to the
device. The XY plane bisects the sagittal plane between
3.2.10 nucleus device, n—A generic term that refers to all
superior and inferior surfaces that are intended to simulate the
types of devices intended to replace or augment the nucleus
adjacent vertebral endplates. The positive X axis is to be
pulposus in the intervertebral disc.Adjectives can be added to
directed anteriorly. The positive Z axis is to be directed
the term “nucleus device” to more thoroughly describe the
superiorly. Shear components of loading are defined to be the
device’s intended function. Terms 3.2.10.1 through 3.2.10.9
components parallel to the XY plane. The compressive axial
will be used to address specific types of nucleus devices
force is defined to be the component in either the positive or
throughouttherestofthisguide.Thesetermsmaynotapplyto
negative Z direction depending on the test frame set-up.
all nucleus devices and some combinations of terms may be
Torsional load is defined as the component of moment about
applicabletocertaindevices.However,thistermshouldnotbe
the Z axis.
used interchangeably with annular repair device.
3.2.2 energy absorption, n—The work or energy (in joules)
3.2.10.1 complete nucleus replacement device, n—A
that a material can store, temporarily or permanently, after a
nucleus device that is designed to replace most or all (≥50%
given stress is applied and then released.
by volume) of the nucleus pulposus of the intervertebral disc.
3.2.3 expulsion, n—a condition during testing when the
3.2.10.2 partial nucleus replacement device, n—A nucleus
deviceoracomponentofthedevicebecomesfullydisplacedor
device that is designed to replace some (<50% by volume) of
dislodged from its implanted position (that is, in the direction
the nucleus pulposus of the intervertebral disc.
of shear) through a surrogate annulus, or enclosure used to
3.2.10.3 nucleus augmentation device, n—Anucleus device
simulate an annular boundary. Expulsion may be considered a
that is designed to supplement or augment, but not replace, the
specific type of migration and for the purposes of this standard
existing nucleus pulposus in the intervertebral disc.
is only useful when the testing is being conducted within a
surrogate annulus or enclosure. 3.2.10.4 encapsulated nucleus device, n—A nucleus device
that includes an outer jacket, bag, or a similar casing, which in
3.2.4 extrusion, n—a condition during testing when a por-
turn interfaces directly with the in vivo environment.
tion of a device displaces through a surrounding membrane or
enclosure but does not separate from the rest of the device.
3.2.10.5 open nucleus device, n—A nucleus device that is
Extrusion may be considered a specific type of migration and
not encased. The material interfaces directly with the in vivo
forthepurposesofthisstandardisonlyusefulwhenthetesting
environment.
is being conducted within a surrogate annulus or enclosure.
3.2.10.6 in situ formed nucleus device, n—Anucleus device
that is introduced into the disc space without a predetermined
geometry. This may include injectable, in situ curing or
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. polymerizing nucleus devices.
F2789 − 10 (2015)
3.2.10.7 preformed nucleus device, n—A nucleus device Table 1 also lists additional reference documents that may be
that is introduced into the disc space already in a applicable to each particular test.
predetermined, but not necessarily final, geometry with all
4.2 Sometestsmaynotbeapplicableforalltypesofnucleus
chemical processes completed prior to insertion.
devices.
3.2.10.8 non-hydrated nucleus device, n—Anucleus device
4.3 Where appropriate, a surrogate annulus may be used to
thatdoesnotrequirewatertobepresenttoachieveitsintended
further characterize the nucleus device.
purposes.
4.4 Alltestsshallbeperformedonthenucleusdeviceinthe
3.2.10.9 hydrated nucleus device, n—Anucleus device that
same shape, size, and condition as it would be used clinically
requires water to be present to achieve its intended purposes.
unless adequately justified (that is, if gamma radiation is to be
3.2.11 Range of Motion (ROM), n—The difference between
used to sterilize the device, or the device is meant to function
the minimum and maximum displacement or angular displace-
in a hydrated state, then all tests should be performed on
ment of the nucleus device that occurs during a test. This
gamma-irradiated or hydrated parts or a justification shall be
parameter may be useful when a surrogate annulus is used for
made).
testing.
4.5 Nucleus devices shall be tested statically to failure and
3.2.12 secant stiffness, n—For a given applied load or
also tested cyclically to estimate the maximum run out load or
applied displacement: [(maximum load) – (minimum load)]/
momentat10×10 cycles.Dependingonthetestandintended
[(maximum displacement) – (minimum displacement)].
use, the devices can be tested in force control or in position
3.2.13 stiffness, n—The slope of the linear portion of the
control,butineithercase,thecontrolmodeshouldbejustified.
load-displacement curve or of the moment-angular displace-
mentcurveatasegmentwithinnormalphysiologicparameters.
5. Significance and Use
If there is no linear portion, then stiffness may be estimated
5.1 Nucleus devices are generally designed to augment the
using other standard methods such as those found in Test
mechanical function of native degenerated nucleus material or
Method E111 (chord or tangential stiffness, or both) within
to replace tissue that has been removed during a surgical
normal physiologic parameters.
procedure. This guide outlines methods for evaluating many
3.2.14 subsidence, n—Settling or migration of the device
different types of devices. Comparisons between devices must
into the inferior or superior interfaces adjacent to the device.
be made cautiously and with careful analysis, taking into
Subsidencemaybeconsideredaspecifictypeofmigrationand,
account the effects that design and functional differences can
for the purposes of this standard, is only useful when the
have on the testing configurations and overall performance,
matingendplates,fixturesorsurrogateannulushaveamodulus
andthepossibilitythatmechanicalfailuremaynotberelatedto
that allows subsidence to occur.
clinical failure and inversely, that mechanical success may not
be related to clinical success.
4. Summary of Test Method
5.2 These tests are conducted in vitro to allow for analysis
4.1 The tests for characterizing the performance of nucleus
of the mechanical performance of the nucleus device under
devices can include one or more of the following: static and
specific testing modalities. The loads applied may differ from
dynamic axial compression, axial torsion, and shear tests,
thecomplexloadingseeninvivo,andthereforetheresultsfrom
functional range of motion, subsidence, mechanical behavior
these tests may not directly predict in vivo performance.
change due to aging, swelling pressure, and viscoelastic
testing. Table 1 summarizes these tests with reference to 5.3 These tests are used to quantify the static and dynamic
sections where they are described in more detail.Additionally, properties and performance of different implant designs. The
TABLE 1 Summary of Test Methods
Test Grouping Test Type Boundary and Sample Section of this Standard Applicable Standard or
Conditions Reference
Static Axial Compression As Manufactured 7.2 Test Methods F2346
Axial T
...
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: F2789 − 10 F2789 − 10 (Reapproved 2015)
Standard Guide for
Mechanical and Functional Characterization of Nucleus
Devices
This standard is issued under the fixed designation F2789; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This guide describes various forms of nucleus replacement and nucleus augmentation devices. It further outlines the types
of testing that are recommended in evaluating the performance of these devices.
1.2 Biocompatibility of the materials used in a nucleus replacement device is not addressed in this guide. However, users should
investigate the biocompatibility of their device separately (see X1.1).
1.3 While it is understood that expulsion and endplate fractures represent documented clinical failures, this guide does not
specifically address them, although some of the factors that relate to expulsion have been included (see X1.3).
1.4 Multiple tests are described in this guide; however, the user need not use them all. It is the responsibility of the user of this
guide to determine which tests are appropriate for the devices being tested and their potential application. Some tests may not be
applicable for all types of devices. Moreover, some nucleus devices may not be stable in all test configurations. However, this does
not necessarily mean that the test methods described are unsuitable.
1.5 The science of nucleus device design is still very young and includes technology that is changing more quickly than this
guide can be modified. Therefore, the user must carefully consider the applicability of this guide to the user’s particular device;
the guide may not be appropriate for every device. For example, at the time of publication, this guide does not address the nucleus
replacement and nucleus augmentation devices that are designed to be partially or completely resorbable in the body. However,
some of the test recommended in this guide may be applicable to evaluate such devices. It has not been demonstrated that
mechanical failure of nucleus devices is related to adverse clinical results. Therefore this standard should be used with care in
evaluating proposed nucleus devices.
1.6 This guide is not intended to be a performance standard. It is the responsibility of the user of this guide to characterize the
safety and effectiveness of the nucleus device under evaluation.
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
Angular measurements may be reported in 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 appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D2990 Test Methods for Tensile, Compressive, and Flexural Creep and Creep-Rupture of Plastics
D6204 Test Method for Rubber—Measurement of Unvulcanized Rheological Properties Using Rotorless Shear Rheometers
E6 Terminology Relating to Methods of Mechanical Testing
E111 Test Method for Young’s Modulus, Tangent Modulus, and Chord Modulus
E132 Test Method for Poisson’s Ratio at Room Temperature
E328 Test Methods for Stress Relaxation for Materials and Structures
This test method is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility of Subcommittee
F04.25 on Spinal Devices.
Current edition approved June 1, 2010May 1, 2015. Published July 2010 July 2015. Originally approved in 2010. Last previous edition approved in 2010 as F2789 – 10.
DOI: 10.1520/F2789–10. 10.1520/F2789-10R15.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2789 − 10 (2015)
E1823 Terminology Relating to Fatigue and Fracture Testing
F561 Practice for Retrieval and Analysis of Medical Devices, and Associated Tissues and Fluids
F1582 Terminology Relating to Spinal Implants
F1714 Guide for Gravimetric Wear Assessment of Prosthetic Hip Designs in Simulator Devices
F1877 Practice for Characterization of Particles
F1980 Guide for Accelerated Aging of Sterile Barrier Systems for Medical Devices
F2267 Test Method for Measuring Load Induced Subsidence of Intervertebral Body Fusion Device Under Static Axial
Compression
F2346 Test Methods for Static and Dynamic Characterization of Spinal Artificial Discs
F2423 Guide for Functional, Kinematic, and Wear Assessment of Total Disc Prostheses
2.2 Other Standards:
ISO 10993 Biological Evaluation of Medical Devices: Parts 1–20
ISO 18192–1 Implants for Surgery—Wear of Total Intervertebral Spinal Disc Prostheses
3. Terminology
3.1 For definition of terms, refer to Terminologies E6, E1823, and F1582.
3.2 Definitions:
3.2.1 coordinate system/axes, n—Three orthogonal axes are defined by Terminology F1582. The center of the coordinate system
is located at the geometric center of the native disc. Because of design intent, or procedural limitations, the device might not be
implanted at the center of the native disc; therefore, the geometric center of the disc might not be the geometric center of the device.
For uniformity in comparison between devices, it is important that the origin be placed with respect to the disc, not the device.
This is done so that all loading is consistently applied and measurement made with respect to the anatomy of the spine, and not
with respect to the device. The XY plane bisects the sagittal plane between superior and inferior surfaces that are intended to
simulate the adjacent vertebral endplates. The positive X axis is to be directed anteriorly. The positive Z axis is to be directed
superiorly. Shear components of loading are defined to be the components parallel to the XY plane. The compressive axial force
is defined to be the component in either the positive or negative Z direction depending on the test frame set-up. Torsional load is
defined as the component of moment about the Z axis.
3.2.2 energy absorption, n—The work or energy (in joules) that a material can store, temporarily or permanently, after a given
stress is applied and then released.
3.2.3 expulsion, n—a condition during testing when the device or a component of the device becomes fully displaced or
dislodged from its implanted position (that is, in the direction of shear) through a surrogate annulus, or enclosure used to simulate
an annular boundary. Expulsion may be considered a specific type of migration and for the purposes of this standard is only useful
when the testing is being conducted within a surrogate annulus or enclosure.
3.2.4 extrusion, n—a condition during testing when a portion of a device displaces through a surrounding membrane or
enclosure but does not separate from the rest of the device. Extrusion may be considered a specific type of migration and for the
purposes of this standard is only useful when the testing is being conducted within a surrogate annulus or enclosure.
3.2.5 fatigue life, n—The number of cycles, N, that the nucleus device can sustain at a particular load or moment before
functional or mechanical failure occurs.
3.2.6 functional failure, n—A failure that renders the nucleus device ineffective or unable to resist load or function as
predetermined within desired parameters (for example, permanent deformation, dissociation, dehydration, expulsion, extrusion or
fracture), or both.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
3.2.6.1 Discussion—
Functional failure may or may not be correlated with clinical failure.
3.2.7 hysteresis, n—The resultant loop on a force displacement plot that is created from a mechanical test performed on a
viscoelastic material. The area inside the loop can be used to determine the energy absorption.
3.2.8 mechanical failure, n—A failure associated with the onset of a defect in the material (for example, a fatigue fracture, a
static fracture, or surface wear).
3.2.8.1 Discussion—
A mechanical failure can occur without there being a functional failure.
F2789 − 10 (2015)
3.2.9 migration, n—A condition during testing when a device displaces from its original position during testing. Migration may
or may not be considered a specific type of functional failure. The user is expected to define their criteria for acceptable levels of
migration and provide rationale for those criteria. See also definitions for expulsion, extrusion, and subsidence.
3.2.10 nucleus device, n—A generic term that refers to all types of devices intended to replace or augment the nucleus pulposus
in the intervertebral disc. Adjectives can be added to the term “nucleus device” to more thoroughly describe the device’s intended
function. Terms 3.2.10.1 through 3.2.10.9 will be used to address specific types of nucleus devices throughout the rest of this guide.
These terms may not apply to all nucleus devices and some combinations of terms may be applicable to certain devices. However,
this term should not be used interchangeably with annular repair device.
3.2.10.1 complete nucleus replacement device, n—A nucleus device that is designed to replace most or all (≥ 50 % by volume)
of the nucleus pulposus of the intervertebral disc.
3.2.10.2 partial nucleus replacement device, n—A nucleus device that is designed to replace some (< 50 % by volume) of the
nucleus pulposus of the intervertebral disc.
3.2.10.3 nucleus augmentation device, n—A nucleus device that is designed to supplement or augment, but not replace, the
existing nucleus pulposus in the intervertebral disc.
3.2.10.4 encapsulated nucleus device, n—A nucleus device that includes an outer jacket, bag, or a similar casing, which in turn
interfaces directly with the in vivo environment.
3.2.10.5 open nucleus device, n—A nucleus device that is not encased. The material interfaces directly with the in vivo
environment.
3.2.10.6 in situ formed nucleus device, n—A nucleus device that is introduced into the disc space without a predetermined
geometry. This may include injectable, in situ curing or polymerizing nucleus devices.
3.2.10.7 preformed nucleus device, n—A nucleus device that is introduced into the disc space already in a predetermined, but
not necessarily final, geometry with all chemical processes completed prior to insertion.
3.2.10.8 non-hydrated nucleus device, n—A nucleus device that does not require water to be present to achieve its intended
purposes.
3.2.10.9 hydrated nucleus device, n—A nucleus device that requires water to be present to achieve its intended purposes.
3.2.11 Range of Motion (ROM), n—The difference between the minimum and maximum displacement or angular displacement
of the nucleus device that occurs during a test. This parameter may be useful when a surrogate annulus is used for testing.
3.2.12 secant stiffness, n—For a given applied load or applied displacement: [(maximum load) – (minimum load)]/[(maximum
displacement) – (minimum displacement)].
3.2.13 stiffness, n—The slope of the linear portion of the load-displacement curve or of the moment-angular displacement curve
at a segment within normal physiologic parameters. If there is no linear portion, then stiffness may be estimated using other
standard methods such as those found in Test Method E111 (chord or tangential stiffness, or both) within normal physiologic
parameters.
3.2.14 subsidence, n—Settling or migration of the device into the inferior or superior interfaces adjacent to the device.
Subsidence may be considered a specific type of migration and, for the purposes of this standard, is only useful when the mating
endplates, fixtures or surrogate annulus have a modulus that allows subsidence to occur.
4. Summary of Test Method
4.1 The tests for characterizing the performance of nucleus devices can include one or more of the following: static and dynamic
axial compression, axial torsion, and shear tests, functional range of motion, subsidence, mechanical behavior change due to aging,
swelling pressure, and viscoelastic testing. Table 1 summarizes these tests with reference to sections where they are described in
more detail. Additionally, Table 1 also lists additional reference documents that may be applicable to each particular test.
4.2 Some tests may not be applicable for all types of nucleus devices.
4.3 Where appropriate, a surrogate annulus may be used to further characterize the nucleus device.
4.4 All tests shall be performed on the nucleus device in the same shape, size, and condition as it would be used clinically unless
adequately justified (that is, if gamma radiation is to be used to sterilize the device, or the device is meant to function in a hydrated
state, then all tests should be performed on gamma-irradiated or hydrated parts or a justification shall be made).
4.5 Nucleus devices shall be tested statically to failure and also tested cyclically to estimate the maximum run out load or
moment at 10 × 10 cycles. Depending on the test and intended use, the devices can be tested in force control or in position control,
but in either case, the control mode should be justified.
5. Significance and Use
5.1 Nucleus devices are generally designed to augment the mechanical function of native degenerated nucleus material or to
replace tissue that has been removed during a surgical procedure. This guide outlines methods for evaluating many different types
F2789 − 10 (2015)
TABLE 1 Summary of Test Methods
Test Grouping Test Type Boundary and Sample Section of this Standard Applicable Standard or
Conditions Reference
Static Axial Compression As Manufactured 7.2 Test Methods F2346
Axial Torsion With Surrogate Annulus 7.1 and 7.2
Shear Simulated Aged 7.2 and 7.7
Bending With Surrogate Annulus 7.1, 7.2, and 7.7
and Simul
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