ASTM F2346-05(2011)
(Test Method)Standard Test Methods for Static and Dynamic Characterization of Spinal Artificial Discs
Standard Test Methods for Static and Dynamic Characterization of Spinal Artificial Discs
SIGNIFICANCE AND USE
Artificial intervertebral discs are orthopaedic implants that replace degenerated natural intervertebral discs. Their function is to support the anterior column of the spine while allowing motion at the operated level. These test methods outline materials and methods for the characterization of the mechanical performance of different artificial intervertebral discs so that comparisons can be made between different designs.
These test methods are designed to quantify the static and dynamic characteristics of different designs of artificial intervertebral discs. These tests are conducted in vitro in order to allow for analysis of individual disc replacement devices and comparison of the mechanical performance of multiple artificial intervertebral disc designs in a standard model.
The loads applied to the artificial intervertebral discs may differ from the complex loading seen in vivo, and therefore, the results from these tests may not directly predict in vivo performance. The results, however, can be used to compare mechanical performance of different artificial intervertebral discs.
Fatigue tests should be conducted in a 0.9 % saline environmental bath at 37°C at a rate of 2 Hz or less. Other test environments such as a simulated body fluid, a saline drip or mist, distilled water, or other type of lubrication could also be used with adequate justification. Likewise, alternative test frequencies may be used with adequate justification.
It is well known that the failure of materials is dependent upon stress, test frequency, surface treatments, and environmental factors. Therefore, when determining the effect of changing one of these parameters (for example, frequency, material, or environment), all others should be kept constant to facilitate interpretation of the results. In particular, it may be necessary to assess the influence of test frequency on device fracture while holding the test environment, implant materials and processing, and implant geometry con...
SCOPE
1.1 These test methods specify the materials and methods for the static and dynamic testing of artificial intervertebral discs.
1.2 These test methods are intended to provide a basis for the mechanical comparison among past, present, and future non-biologic artificial intervertebral discs. These test methods allow comparison of artificial intervertebral discs with different intended spinal locations (cervical, thoracic, and lumbar) and methods of application to the intervertebral spaces. These test methods are intended to enable the user to mechanically compare artificial intervertebral discs and do not purport to provide performance standards for artificial intervertebral discs.
1.3 These test methods describe static and dynamic tests by specifying load types and specific methods of applying these loads. These tests are designed to allow for the comparative evaluation of artificial intervertebral discs.
1.4 These test methods do not purport to address all clinically relevant failure modes for artificial intervertebral discs, some of which will be device specific. For example, these test methods do not address the implant's resistance to expulsion or implant wear resistance under expected in vivo loads and motions. In addition, the biologic response to wear debris is not addressed in these test methods.
1.5 Requirements are established for measuring displacements, determining the yield load or moment, and evaluating the stiffness of artificial intervertebral discs.
1.6 Some artificial intervertebral discs may not be testable in all test configurations.
1.7 The values stated in SI units are to be regarded as the standard with the exception of angular measurements, which may be reported in terms of either degrees or radians.
1.8 The use of this standard may involve the operation of potentially hazardous equipment. This standard does not purport to address all of the safety concerns, if any, associated with it...
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Designation:F2346 −05 (Reapproved 2011)
Standard Test Methods for
Static and Dynamic Characterization of Spinal Artificial
Discs
This standard is issued under the fixed designation F2346; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.8 The use of this standard may involve the operation of
potentially hazardous equipment. This standard does not pur-
1.1 These test methods specify the materials and methods
port to address all of the safety concerns, if any, associated
for the static and dynamic testing of artificial intervertebral
with its use. It is the responsibility of the user of this standard
discs.
to establish appropriate safety and health practices and
1.2 These test methods are intended to provide a basis for
determine the applicability of regulatory limitations prior to
the mechanical comparison among past, present, and future
use.
non-biologic artificial intervertebral discs. These test methods
allowcomparisonofartificialintervertebraldiscswithdifferent
2. Referenced Documents
intended spinal locations (cervical, thoracic, and lumbar) and
2.1 ASTM Standards:
methods of application to the intervertebral spaces. These test
E4 Practices for Force Verification of Testing Machines
methods are intended to enable the user to mechanically
E6 Terminology Relating to Methods of Mechanical Testing
compare artificial intervertebral discs and do not purport to
E466 Practice for Conducting Force Controlled Constant
provide performance standards for artificial intervertebral
Amplitude Axial Fatigue Tests of Metallic Materials
discs.
E467 Practice for Verification of Constant Amplitude Dy-
1.3 These test methods describe static and dynamic tests by namic Forces in an Axial Fatigue Testing System
specifying load types and specific methods of applying these E468 Practice for Presentation of Constant Amplitude Fa-
loads. These tests are designed to allow for the comparative
tigue Test Results for Metallic Materials
evaluation of artificial intervertebral discs. E1823 TerminologyRelatingtoFatigueandFractureTesting
F1582 Terminology Relating to Spinal Implants
1.4 These test methods do not purport to address all clini-
F2077 TestMethodsForIntervertebralBodyFusionDevices
cally relevant failure modes for artificial intervertebral discs,
some of which will be device specific. For example, these test
3. Terminology
methodsdonotaddresstheimplant’sresistancetoexpulsionor
3.1 All definitions below supersede definitions contained
implant wear resistance under expected in vivo loads and
within Terminologies E6, E1823, F1582, and Practices E466,
motions.Inaddition,thebiologicresponsetoweardebrisisnot
E467.
addressed in these test methods.
3.2 Definitions:
1.5 Requirements are established for measuring
3.2.1 artificial intervertebral disc—a synthetic structure that
displacements, determining the yield load or moment, and
is permanently implanted in the disc space between two
evaluating the stiffness of artificial intervertebral discs.
adjacent vertebral bodies to provide spinal column support and
1.6 Some artificial intervertebral discs may not be testable
allow intervertebral motion.
in all test configurations.
3.2.2 coordinate system/axes—three orthogonal axes are
1.7 The values stated in SI units are to be regarded as the
defined by Terminology F1582. The center of the coordinate
standard with the exception of angular measurements, which
system is located at the geometric center of the artificial
may be reported in terms of either degrees or radians.
intervertebraldisc.Alternativecoordinatesystemsmaybeused
with justification. The XY-plane is to bisect the superior and
inferior surfaces that are intended to simulate the adjacent
These test methods are under the jurisdiction of ASTM Committee F04 on
Medical and Surgical Materials and Devicesand 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, 2011. Published January 2012. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2005. Last previous edition approved in 2005 as F2346 – 05. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/F2346-05R11. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2346−05 (2011)
FIG. 1Intervertebral Height Diagram
vertebral end plates. The positive Z-axis is to be directed vertebral bodies: minimum height of 2 mm and maximum
3,4
perpendicular to the bisector of the disc space, oriented in the height of 16.5 mm. See Fig. 1.
superior direction. The positive X-axis is parallel to the
3.2.9 load point—the point through which the resultant
intervertebral space, oriented in the anterior direction and the
force on the intervertebral device passes; that is, the geometric
positive Y-axis is parallel to the disc space, oriented in the left
center of the superior fixture’s sphere (see Figs. 2-4).
direction. Force components parallel to the XY-plane are shear
3.2.10 maximum run-out load or moment—the maximum
components of loading. The compressive axial force is defined
load or moment for a given test that can be applied to an
to be the component in the negative Z direction. Torsional load
artificial intervertebral disc where all of the tested constructs
is defined to be the component of moment parallel to the
have withstood 10 000 000 cycles without functional failure.
Z-axis.
3.2.11 mechanical deterioration—deterioration that is vis-
3.2.3 fatigue life—the number of cycles, N, that the artificial
ibletothenakedeyeandisassociatedwithmechanicaldamage
intervertebral disc can sustain at a particular load or moment
to the device under test (for example, initiation of fatigue crack
before functional failure occurs.
or surface wear).
3.2.4 functional failure—permanent deformation that ren-
3.2.12 offset angular displacement—(distance OB—Fig. 6)
ders the artificial intervertebral disc ineffective or unable to
offset on the angular displacement axis equal to 2 % of the
adequately resist load.
intervertebral height, H, divided by the maximum radius of the
3.2.5 ideal insertion location—the location of the artificial
implant in the XY-plane; for example, for an artificial interver-
disc in the intervertebral space that is suggested in the
tebral disc with a height of 10 mm and a maximum radius in
manufacturer’s surgical installation instructions. The ideal
the XY-plane of 9 mm, distance OB = (0.02) (10 mm) / (9 mm)
insertion location is to be described with respect to the
= 0.022 radians = 1.3°.
simulated inferior and superior vertebral bodies (polyacetal or
3.2.13 offset displacement—(distance OB—Fig. 6) offset on
metal blocks) and will be dictated by the device design.
the linear displacement axis equal to 2 % of the intervertebral
3.2.6 intended method of application—artificial interverte-
height (for example, 0.2 mm for a 10 mm intervertebral
bral discs may contain different types of features to stabilize
height).
the implant-tissue interface such as threads, spikes, and tex-
3.2.14 permanent deformation—the remaining linear or an-
tured surfaces. Each type of feature has an intended method of
gular displacement (axial—mm, angular—degrees or radians)
application or attachment to the spine.
relative to the initial unloaded condition of the artificial
3.2.7 intended spinal location—the anatomic region of the
intervertebral disc after the applied load or moment has been
spine intended for the artificial intervertebral disc. Artificial removed.
intervertebraldiscsmaybedesignedanddevelopedforspecific
3.2.15 stiffness (axial—n/mm, angular—n·mm/degree or
regions of the spine such as the cervical, thoracic, and lumbar
n·mm/radian)—the slope of the initial linear portion of the
spine. Also, since different surgical approaches may exist, the
description of the intended spinal location should include both
the indicated spinal levels and the ideal insertion locations
Nissan, M., Gilad, I., “The Cervical and Lumbar Vertebrae—AnAnthropomet-
ric Model,” Engineering In Medicine, Vol 13, No. 3, 1984, pp. 111–114.
within the intervertebral space allowed at each level.
Lu, J., Ebraheim, N.A., Yang, H., Rollins, J., and Yeasting, R. A., “Anatomic
3.2.8 intervertebral height—the minimum distance parallel
BasesforAnteriorSpinalSurgery:SurgicalAnatomyoftheCervicalVertebralBody
to the Z-axis in the YZ-plane between the unaltered simulated and Disc Space,” Surg Radiol Anat, Vol 21, No. 4, 1999, pp. 235–239.
F2346−05 (2011)
FIG. 2Compression Testing Configuration
load-displacement curve or the slope of the initial linear offset displacement or offset angular displacement. This is
portion of the moment-angular displacement curve. This is illustrated as the distance OA in Fig. 6.
illustrated as the slope of the line OG in Fig. 6. If the device
3.2.20 yield load or moment—the applied load, F,or
does not exhibit a linear initial load/displacement curve, the
moment, M, transmitted by the pushrod (assumed equal to
displacement should be reported at 30 %, 60 %, and 90 % of
force component parallel to and indicated by load or torque
the yield load or moment.
cell) required to produce a permanent deformation equal to the
3.2.16 test block—the component of the test apparatus for offset displacement or the offset angular displacement. This is
mounting the artificial intervertebral disc in the intended test illustrated as point D in Fig. 6.
configuration.
4. Summary of Test Methods
3.2.17 ultimate displacement (axial—mm, angular—
4.1 These test methods are proposed for the mechanical
degrees or radians)—the linear or angular displacement asso-
testing of artificial intervertebral discs specific to the cervical,
ciated with the ultimate load or ultimate moment. This is
thoracic, and lumbar spine.
illustrated as the displacement, OF, in Fig. 6.
4.2 All tests are to be performed on the prosthesis size with
3.2.18 ultimate load or moment (axial—n, angular—
the smallest safety factor for the levels indicated for implan-
n·mm)—the maximum applied load, F, or moment, M, trans-
tation. If this worst-case size cannot be determined using
mitted by the pushrod (assumed equal to force and moment
theoretical or experimental methods such as simple stress
component parallel to and indicated by load or torque cell) to
calculations or finite element analysis, then all available sizes
the artificial intervertebral disc assembly. This is illustrated as
are to be tested and the complete range of results are to be
point E in Fig. 6.
reported.
3.2.19 yield displacement—the linear displacement (mm) or
angular displacement (degrees or radians) when an artificial 4.3 Fatigue testing of the artificial intervertebral discs will
intervertebral disc has a permanent deformation equal to the simulate a motion segment via a gap between two polyacetal
F2346−05 (2011)
FIG. 3Compression/Shear Testing Configuration
test blocks. The polyacetal will eliminate the effects of the function is to support the anterior column of the spine while
variability of bone properties and morphology for the fatigue allowing motion at the operated level. These test methods
tests. The minimum ultimate tensile strength of the polyacetal outline materials and methods for the characterization of the
blocks shall be no less than 61 MPa. mechanical performance of different artificial intervertebral
discs so that comparisons can be made between different
4.4 Static testing of the artificial intervertebral discs will
designs.
simulate a motion segment via a gap between two stainless
steel blocks. The minimum tensile yield strength of the blocks 5.2 These test methods are designed to quantify the static
shall be no less than 1170 MPa.
and dynamic characteristics of different designs of artificial
intervertebral discs. These tests are conducted in vitro in order
4.5 The pushrod shall be manufactured from stainless steel
toallowforanalysisofindividualdiscreplacementdevicesand
having minimum tensile yield stress of 1170 MPa and be of
comparison of the mechanical performance of multiple artifi-
minimum cross-sectional area that would produce a compres-
cial intervertebral disc designs in a standard model.
sive yield strength of at least 25 000 N.
5.3 The loads applied to the artificial intervertebral discs
4.6 Static and dynamic tests will evaluate the artificial
may differ from the complex loading seen in vivo, and
intervertebral disc. The user of these test methods must decide
therefore, the results from these tests may not directly predict
which series of tests are applicable to the artificial interverte-
in vivo performance. The results, however, can be used to
bral disc in question. The user of these test methods may
compare mechanical performance of different artificial in-
choose to use all or a selection of the tests described in these
tervertebral discs.
test methods for testing a particular artificial intervertebral
disc. For example, the torsion test method may not apply to a 5.4 Fatigue tests should be conducted in a 0.9 % saline
device that has no mechanical resistance in axial rotation.
environmental bath at 37°C at a rate of 2 Hz or less. Other test
environments such as a simulated body fluid, a saline drip or
5. Significance and Use
mist, distilled water, or other type of lubrication could also be
5.1 Artificial intervertebral discs are orthopaedic implants used with adequate justification. Likewise, alternative test
that replace degenerated natural intervertebral discs. Their frequencies may be used with adequate justification.
F2346−05 (2011)
FIG. 4Torsion Testing Configuration with a Pin-Slot Gimbal
FIG. 5Polyacetal or Metal Test Block
5.5 It is well known that the failure of materials is depen- changing one of these parameters (for example, frequency,
dent upon stress, test frequency, surface treatments, and envi- material, or environment), all others should be kept constant to
ronmental factors. Therefore, when determining the effect of facilitate interpretation of the results. In particular, it may be
F2346−05 (2011)
FIG. 6Typical Load Displacement Curve
necessary to assess the influence of test frequency on device methods should select the intervertebral height that is appro-
fracture while
...
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