ASTM F2790-10
(Practice)Standard Practice for Static and Dynamic Characterization of Motion Preserving Lumbar Total Facet Prostheses
Standard Practice for Static and Dynamic Characterization of Motion Preserving Lumbar Total Facet Prostheses
SIGNIFICANCE AND USE
Facet Prosthesis Components—The facet replacement may comprise a variety of shapes and configurations. Its forms may include, but are not limited to, ball and socket articulating joints, joints having a free-floating or semi-constrained third body, metallic load-bearing surfaces, and spring and dampening mechanisms. Additionally, it may be a unilateral or bilateral design.
These test methods are designed to quantify the static and dynamic characteristics of different designs of FP. The tests are conducted in vitro in order to allow for analysis of individual devices and comparison of the mechanical performance of multiple designs.
The loads applied to the FP 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 in different devices.
Fatigue testing in a simulated body fluid or saline may cause fretting, corrosion, or lubricate the interconnections and thereby affect the relative performance of tested devices. This test should be conducted in a 0.9 % saline environmental bath at 37°C at a maximum rate of 10 Hz for all metallic devices and 2 Hz for non-metallic devices. Other test environments such as a simulated body fluid, a saline drip or mist, distilled water, other type of lubrication or dry could also be used with adequate justification. Likewise, alternative test frequencies may be used with adequate justification to ensure that it does not impact the device performance.
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 these parameters (for example, frequency, material, or environment), care should be taken to allow for appropriate interpretation of the results. In particular, it may be necessary to assess the influence of test frequency on device fracture while hold...
SCOPE
1.1 This practice provides guidance for the static and dynamic testing of Lumbar Total Facet Prostheses (FP). These implants are intended to allow motion and lend support to one or more functional spinal unit(s) through replacement of the natural facets.
1.2 These test methods are intended to provide a basis for the mechanical comparison among past, present, and future non-biologic FP. These test methods allow comparison of devices with different methods of application to the lumbar spine. These test methods are intended to enable the user to mechanically compare devices and do not purport to provide performance standards for them.
1.3 These test methods describe static and dynamic tests by specifying load types and specific methods of applying these loads.
1.4 These test methods do not purport to address all clinically relevant failure modes for FP, some of which will be device specific. For example, these test methods do not address 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 and evaluating the stiffness of FP.
1.6 Some devices 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 values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
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Designation: F2790 − 10
StandardPractice for
Static and Dynamic Characterization of Motion Preserving
Lumbar Total Facet Prostheses
This standard is issued under the fixed designation F2790; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice provides guidance for the static and
D638 Test Method for Tensile Properties of Plastics
dynamic testing of Lumbar Total Facet Prostheses (FP). These
E4 Practices for Force Verification of Testing Machines
implants are intended to allow motion and lend support to one
E6 Terminology Relating to Methods of Mechanical Testing
or more functional spinal unit(s) through replacement of the
E468 Practice for Presentation of Constant Amplitude Fa-
natural facets.
tigue Test Results for Metallic Materials
1.2 These test methods are intended to provide a basis for
E739 PracticeforStatisticalAnalysisofLinearorLinearized
the mechanical comparison among past, present, and future
Stress-Life (S-N) and Strain-Life (´-N) Fatigue Data
non-biologic FP. These test methods allow comparison of
F1582 Terminology Relating to Spinal Implants
devices with different methods of application to the lumbar
spine. These test methods are intended to enable the user to
3. Terminology
mechanically compare devices and do not purport to provide
3.1 All functional and kinematic testing terminology is
performance standards for them.
consistent with the referenced standards (including Teminol-
1.3 These test methods describe static and dynamic tests by
ogy E6 and Terminology F1582), unless otherwise stated.
specifying load types and specific methods of applying these
3.2 Definitions:
loads.
3.2.1 coordinate systems/axes—Global XYZorthogonalaxes
1.4 These test methods do not purport to address all clini-
are defined following a right-handed Cartesian coordinate
cally relevant failure modes for FP, some of which will be
system in which the XY plane is parallel to and co-planar with
devicespecific.Forexample,thesetestmethodsdonotaddress
the superior endplate of the inferior vertebral body.Alternative
implant wear resistance under expected in vivo loads and
coordinate systems may be used with justification. The global
motions.Inaddition,thebiologicresponsetoweardebrisisnot
axes are fixed relative to the inferior vertebral body. Lower
addressed in these test methods.
case letters, xyz, denote a local moving orthogonal coordinate
system attached to the superior vertebral body with directions
1.5 Requirements are established for measuring displace-
initially coincident with those of the global XYZ axes, respec-
ments and evaluating the stiffness of FP.
tively. The 3D motion of the superior relative to inferior
1.6 Some devices may not be testable in all test configura-
vertebra is specified and is to be measured in terms of
tions.
sequential Eulerian angular rotations about the xyz axes,
respectively (z axial rotation, x lateral bend, and y flexion-
1.7 The values stated in SI units are to be regarded as the
extension).
standard with the exception of angular measurements, which
3.2.1.1 origin—center of the global coordinate system that
may be reported in terms of either degrees or radians.
is located at the posterior medial position on the superior
1.8 The values stated in inch-pound units are to be regarded
endplate of the inferior vertebral body.
as standard. The values given in parentheses are mathematical
3.2.1.2 X-axis—positive X-axis is to be directed anteriorly
conversions to SI units that are provided for information only
relative to the specimen’s initial unloaded position.
and are not considered standard.
3.2.1.3 Y-axis—positive Y-axis is directed laterally (toward
the left) relative to the specimen’s initial unloaded position.
ThispracticeisunderthejurisdictionofASTMCommitteeF04onMedicaland
Surgical Materials and Devices and is the direct responsibility of Subcommittee For referenced ASTM standards, visit the ASTM website, www.astm.org, or
F04.25 on Spinal Devices. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Jan. 1, 2010. Published February 2010. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
F2790–10. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2790 − 10
3.2.1.4 Z-axis—positive Z-axis is to be directed superiorly 3.2.7 maximum run-out load or moment—the maximum
relative to the specimen’s initial unloaded position. load or moment for a given test that can be applied to a FP
3.2.2 failure—functional failure or substantial mechanical where all of the tested constructs have withstood 10 000 000
failure. cycles without failure.
3.2.2.1 functional failure—permanent deformation resulting
3.2.8 mechanical deterioration—deterioration that is visible
from fracture, plastic deformation, or loosening beyond the
to the naked eye and is associated with mechanical damage to
ultimate displacement or loosening that renders the spinal
thedeviceundertest(forexample,initiationoffatiguecrackor
implant assembly ineffective or unable to adequately resist
surface wear).
load.
3.2.9 permanent deformation—the remaining linear or an-
3.2.2.2 mechanical failure—failure associated with a defect
gular displacement (axial—mm, angular—degrees or radians)
in the material (for example, fatigue crack) or of the bonding
relative to the initial unloaded condition of the FP after the
between materials that may or may not produce functional
applied load or moment has been removed.
failure.
3.2.10 radius of rotation—the distance between the center
3.2.3 fatigue life—the number of cycles, N, that the FP can
of rotation and the functional position (for example, load-
sustain at a particular load or moment before failure occurs.
bearing contact point) of the FP, for a given motion (that is,
3.2.4 intended method of application—a FP may contain
flexion/extension, lateral bending, or axial rotation).
different types of features to stabilize the implant-tissue inter-
3.2.11 spinal implant assembly—a complete spinal implant
face such as threads, spikes, and textured surfaces. Each type
configuration as intended for surgical use. A spinal implant
of feature has an intended method of application or attachment
assembly may contain anchors, interconnections, and longitu-
to the spine.
dinal elements and may contain transverse elements.
3.2.5 insertion point of an anchor—the location where the
3.2.12 stiffness (axial—N/mm, angular—N·mm/degree or
anchor is attached to the test block.The insertion points shown
N·mm/radian)—the slope of the initial linear portion of the
inFig.1aretobeadheredtoifpossible.Insituationswherethe
load-displacement curve or the slope of the initial linear
design of the spinal implant assembly or the manufacturer’s
portion of the moment-angular displacement curve. This is
surgical instructions for installation dictate otherwise, the
illustratedastheslopeoftheline OGinFig.2.Thedevicemay
attachment points may deviate from these dimensions.
not exhibit an isolated linear portion on the load/displacement
3.2.6 longitudinal direction—the initial spatial orientation
curve, due to the complicated nature of these devices.As such,
between the insertion points in the superior test blocks and the
these data are information only.
inferior test blocks.
FIG. 1 UHMWPE Test Block FIG. 2 Typical Load Displacement Curve
F2790 − 10
3.2.13 superior/inferior spinal implant construct—the supe- 4.2 All tests are to be performed on the prosthesis size with
rior or inferior spinal implant assembly attached to the test the smallest safety factor for the levels indicated for implan-
block. tation. If this worst-case size cannot be determined using
theoretical or experimental methods such as simple stress
3.2.14 test block—the component of the test apparatus for
calculations or finite element analysis, then all available sizes
mounting the FP in the intended test configuration.
or a justified selection are to be tested and the complete range
3.2.15 tightening torque—the specified torque that is ap-
of results are to be reported.
plied to the various fasteners of the spinal implant assembly.
4.3 Static and dynamic testing of the devices will simulate a
3.2.16 torsional ultimate load (N·m)—the maximum torque
motion segment via a gap between two Ultra High Molecular
applied to a spinal implant assembly (the torque at Point E in
Weight Polyethylene (UHMWPE) test blocks (Fig. 1, Fig. 3,or
Fig. 2). The ultimate torque should be a function of the device
Fig. 4). The UHMWPE used to manufacture the test blocks
and not of the load cell or testing machine.
should have a tensile breaking strength equal to 40 6 3 MPa
3.2.17 total facet prosthesis—nonbiologic structure in-
(see Specification D638). The UHMWPE will eliminate the
tended to restore the support and motion of the vertebral facet
effectsofthevariabilityofbonepropertiesandmorphologyfor
joint.
the fatigue tests.
3.2.18 ultimate displacement (axial—mm, angular—
4.4 Static and dynamic tests will evaluate the devices. The
degrees or radians)—the linear or angular displacement asso-
user of this practice must decide which series of tests are
ciated with the ultimate load or ultimate moment. This is
applicable to the device in question. The user of this practice
illustrated as the displacement, OF,in Fig. 2.
may choose to use all or a selection of the tests described for
3.2.19 ultimate load or moment (axial—N, angular—N·mm)
testing a particular device.
—the maximum applied load, F, or moment, M, transmitted to
4.5 This practice is intended to be applicable to FP that
the FP. This is illustrated as point E in Fig. 2.
support and transmit motion by means of an articulating joint
3.2.20 zero displacement intercept (mm)—the intersection
or by use of compliant materials and/or design. Ceramics,
of the straight line section of the load displacement curve and
metals, and/or polymers may be used in FPdesign, and it is the
zero load axis (the zero displacement reference Point O in Fig.
goal of this practice to enable a comparison of these devices,
2).
regardless of material and type of device.
4. Summary of Practice 5. Significance and Use
4.1 This practice is proposed for the mechanical testing of 5.1 Facet Prosthesis Components—The facet replacement
FP. may comprise a variety of shapes and configurations. Its forms
NOTE 1—(A) Anterior-Posterior, (B) Superior-Inferior, (C) Medial-Lateral setups are shown. These setups require one translational actuator and may
require specific fixturing. Test blocks are shown in grey. The arrow indicates the loading direction.
FIG. 3 Diagrams of Possible Test Setups for Translational Loading of a FP
F2790 − 10
NOTE 1—(A) Simulated Flexion-Extension, (B)Axial Rotation, (C) Lateral Bending setups are shown.These setups require one rotational actuator and
may require specific fixturing. The arrow indicates the rotation direction. Test blocks are shown in grey. The position of the axis of rotation should be
based on the information in Table X1.1.
FIG. 4 Diagrams of Possible Test Setups for Rotational Loading of a FP
may include, but are not limited to, ball and socket articulating changing these parameters (for example, frequency, material,
joints, joints having a free-floating or semi-constrained third
or environment), care should be taken to allow for appropriate
body, metallic load-bearing surfaces, and spring and dampen-
interpretation of the results. In particular, it may be necessary
ingmechanisms.Additionally,itmaybeaunilateralorbilateral
to assess the influence of test frequency on device fracture
design.
while holding the test environment, implant materials and
processing, and implant geometry constant.
5.2 These test methods are designed to quantify the static
anddynamiccharacteristicsofdifferentdesignsofFP.Thetests
6. Apparatus and Setup
are conducted in vitro in order to allow for analysis of
individual devices and comparison of the mechanical perfor-
6.1 Test machines will conform to the requirements of
mance of multiple designs.
Practices E4.
5.3 TheloadsappliedtotheFPmaydifferfromthecomplex
6.2 The test apparatus will allow multiple loading regimes
loading seen in vivo, and therefore, the results from these tests
to be applied to all forms of FP.
may not directly predict in vivo performance. The results,
however, can be used to compare mechanical performance in
6.3 The test block should be created according to Fig. 1.
different devices.
Variations from this design to accommodate a device’s fixation
5.4 Fatigue testing in a simulated body fluid or saline may method or features should be reported and justified.
cause fretting, corrosion, or lubricate the interconnections and
6.4 The interpedicular spacing (superior-to-inferior center-
thereby affect the relative performance of tested devices. This
to-center distance between bone anchors) shall be set at 38 mm
test should be conducted in a 0.9 % saline environmental bath
when installing the device and at the beginning of each test.
at37°Catamaximumrateof10Hzforallmetallicdevicesand
The implants should be placed in the UHMWPE blocks
2 Hz for non-metallic devices. Other test environments such as
according to the recommended surgical technique. For devices
a simulated body fluid, a saline drip or mist, distilled water,
that do not require pedicular fixation appropriate test blocks
other type of lubrication or dry could also be used with
should be manufactured to ensure proper evaluation of the
adequate justification. Likewise, alternative test frequencies
fixation components.
may be used with adequate justification to ensure that it does
not impact the device performance.
6.5 Install the FP in the UHMWPE blocks according to the
5.5 It is well known that the failure of materials is depen- manufacturer’s instructions. If necessary, utilize an aluminum
spacer block between the superior and inferior UHMWPE
dent upon stress, test frequency, surface treatments, and envi-
ronmental factors. Therefore, when determining the effect of blocks to fix them with respect to each other during installation
F2790 − 10
and remove after installation is complete. The spacer block differences between the maximum run-out load and a load that
should ensure that the device is installed with t
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