ASTM F2267-04(2011)
(Test Method)Standard Test Method for Measuring Load Induced Subsidence of Intervertebral Body Fusion Device Under Static Axial Compression
Standard Test Method for Measuring Load Induced Subsidence of Intervertebral Body Fusion Device Under Static Axial Compression
SIGNIFICANCE AND USE
Intervertebral body fusion devices are generally simple geometric shaped devices, which are often porous or hollow in nature. Their function is to support the anterior column of the spine to facilitate arthrodesis of the motion segment.
This test method is designed to quantify the subsidence characteristics of different designs of intervertebral body fusion devices since this is a potential clinical failure mode. These tests are conducted in vitro in order to simplify the comparison of simulated vertebral body subsidence induced by the intervertebral body fusion devices.
The static axial compressive loads that will be applied to the intervertebral body fusion devices and test blocks will differ from the complex loading seen in vivo, and therefore, the results from this test method may not be used to directly predict in vivo performance. The results, however, can be used to compare the varying degrees of subsidence between different intervertebral body fusion device designs for a given density of simulated bone.
The location within the simulated vertebral bodies and position of the intervertebral body fusion device with respect to the loading axis will be dependent upon the design and manufacturer's recommendation for implant placement.
SCOPE
1.1 This test method specifies the materials and methods for the axial compressive subsidence testing of non-biologic intervertebral body fusion devices, spinal implants designed to promote arthrodesis at a given spinal motion segment.
1.2 This test method is intended to provide a basis for the mechanical comparison among past, present, and future non-biologic intervertebral body fusion devices. This test method is intended to enable the user to mechanically compare intervertebral body fusion devices and does not purport to provide performance standards for intervertebral body fusion devices.
1.3 This test method describes a static test method by specifying a load type and a specific method of applying this load. This test method is designed to allow for the comparative evaluation of intervertebral body fusion devices.
1.4 Guidelines are established for measuring test block deformation and determining the subsidence of intervertebral body fusion devices.
1.5 Since some intervertebral body fusion devices require the use of additional implants for stabilization, the testing of these types of implants may not be in accordance with the manufacturer's recommended usage.
1.6 Units—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.
1.7 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 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.
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Standards Content (Sample)
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Designation: F2267 − 04 (Reapproved 2011)
Standard Test Method for
Measuring Load Induced Subsidence of Intervertebral Body
Fusion Device Under Static Axial Compression
This standard is issued under the fixed designation F2267; 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 test method specifies the materials and methods for
E4 Practices for Force Verification of Testing Machines
the axial compressive subsidence testing of non-biologic in-
F1582 Terminology Relating to Spinal Implants
tervertebral body fusion devices, spinal implants designed to
F1839 Specification for Rigid Polyurethane Foam for Use as
promote arthrodesis at a given spinal motion segment.
a Standard Material for Testing Orthopaedic Devices and
1.2 This test method is intended to provide a basis for the
Instruments
mechanical comparison among past, present, and future non-
F2077 TestMethodsForIntervertebralBodyFusionDevices
biologic intervertebral body fusion devices.This test method is
intended to enable the user to mechanically compare interver-
3. Terminology
tebral body fusion devices and does not purport to provide
3.1 Allsubsidencetestingterminologyisconsistentwiththe
performance standards for intervertebral body fusion devices.
referenced standards above, unless otherwise stated.
1.3 This test method describes a static test method by
3.2 Definitions:
specifying a load type and a specific method of applying this
3.2.1 coordinate system/axes—three orthogonal axes are
load. This test method is designed to allow for the comparative
defined by Terminology F1582 as seen in Fig. 4. The center of
evaluation of intervertebral body fusion devices.
the coordinate system is located at the geometric center of the
1.4 Guidelines are established for measuring test block
intervertebralbodyfusiondeviceassembly.The X-axisisalong
deformation and determining the subsidence of intervertebral
the longitudinal axis of the implant, with positive X in the
body fusion devices.
anterior direction, Y is lateral, and Z is cephalic.
3.2.2 ideal insertion location—the implant location with
1.5 Since some intervertebral body fusion devices require
respect to the simulated inferior and superior vertebral bodies
the use of additional implants for stabilization, the testing of
(polyurethane)dictatedbythetype,design,andmanufacturer’s
these types of implants may not be in accordance with the
surgical installation instructions.
manufacturer’s recommended usage.
3.2.3 intended method of application—intervertebral body
1.6 Units—The values stated in SI units are to be regarded
fusion devices may contain different types of stabilizing
as the standard with the exception of angular measurements,
features such as threads, spikes, and knurled surfaces. Each
which may be reported in terms of either degrees or radians.
type of feature has an intended method of application or
1.7 The use of this standard may involve the operation of
attachment to the spine.
potentially hazardous equipment. This standard does not pur-
3.2.4 intended spinal location—the anatomic region of the
port to address all of the safety concerns, if any, associated
spine intended for the intervertebral body fusion device.
with its use. It is the responsibility of the user of this standard
Intervertebral body fusion devices may be designed and
to establish appropriate safety and health practices and
developed for specific regions of the spine such as the lumbar,
determine the applicability of regulatory limitations prior to
thoracic, and cervical spine. Also, there potentially exist
use.
different anatomical surgical approaches, which will result in
different implant orientation at different levels of the spine.
This test method is under the jurisdiction ofASTM 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 2003. Last previous edition approved in 2004 as F2267 – 04. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/F2267-04R11. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2267 − 04 (2011)
FIG. 1 Intradiscal Height Diagram
FIG. 2 Typical Load-Displacement Curve with 1.5 mm (Thoracic Device) Offset for Polyurethane Foam Test Blocks
3.2.5 intervertebral subsidence—the process of a vertebral 3.2.6 intradiscal height—the straight-line distance along the
body cavitating or sinking around an implanted intervertebral Z-axis between the unaltered simulated vertebral bodies. See
body fusion device resulting in the loss of intradiscal height. Fig. 1.
F2267 − 04 (2011)
FIG. 3 Typical Load-Displacement Plot Comparison for Test Specimens in Metallic and Polyurethane Test Blocks
3.2.7 load point—the point through which the resultant deformation equal to the offset displacement found by plotting
force on the intervertebral device passes (that is, the geometric line BC with stiffness, K, originating at point B (see Point D in
center of the superior fixture’s sphere) (Fig. 4). Fig. 2).
3.2.8 offset displacement—offset on the displacement axis
4. Summary of Test Method
equal to 1 mm for cervical disc devices, 1.5 mm for thoracic
devices, and 2 mm for lumbar devices (see distanceAB in Fig.
4.1 To measure load induced subsidence, a test method is
2)
proposed for the axial compression of intervertebral body
3.2.9 simulated vertebral bodies—the component of the test
fusion devices specific to the lumbar, thoracic, and cervical
apparatus for mounting the intervertebral body fusion device.
spine.
3.2.10 stiffness, (N/mm)—the slope of the initial linear
4.2 The axial compressive subsidence testing of the in-
portion of the load-displacement curve (see the slope of line
tervertebral body fusion device will be conducted in a simu-
AE in Fig. 2).
lated motion segment via a gap between two polyurethane
3.2.11 test block height—thelineardistancealongthe Z-axis
foam blocks.
fromthetopsurfaceofthesuperiorsimulatedvertebralbodyto
4.3 Grade 15 foam shall be employed conforming to Speci-
thebottomsurfaceoftheinferiorsimulatedvertebralbodywith
fication F1839.
the intervertebral body fusion device in position. The block
heights shall be 70 mm, 60 mm, and 40 mm for lumbar,
5. Significance and Use
thoracic, and cervical intervertebral disc devices respectively.
See Fig. 4.
5.1 Intervertebral body fusion devices are generally simple
3.2.12 yield load—the applied load, F, transmitted by the geometric shaped devices, which are often porous or hollow in
pushrod (assumed equal to force component parallel to and nature. Their function is to support the anterior column of the
indicated by load cell), required to produce a permanent spine to facilitate arthrodesis of the motion segment.
F2267 − 04 (2011)
FIG. 4 Subsidence Test Fixture
5.2 This test method is designed to quantify the subsidence 5. Two pieces of polyurethane foam or rigid metal are rigidly
characteristicsofdifferentdesignsofintervertebralbodyfusion mounted inside the test fixture. The actuator of the testing
devices since this is a potential clinical failure mode. These
machine is connected to the pushrod by a minimal friction ball
tests are conducted in vitro in order to simplify the comparison and socket joint or universal joint (that is, unconstrained in
of simulated vertebral body subsidence induced by the in-
bending). The pushrod is connected to the superior fixture by a
tervertebral body fusion devices.
minimal friction sphere joint (that is, unconstrained in bending
and torsion). The inferior sphere portion firmly holds the
5.3 Thestaticaxialcompressiveloadsthatwillbeappliedto
inferior polyurethane block and is rigidly fixed within the base
the intervertebral body fusion devices and test blocks will
socket so that no rotation occurs. The hollow pushrod and
differ from the complex loading seen in vivo, and therefore, the
superior sphere should be of minimal weight so as to be
resultsfromthistestmethodmaynotbeusedtodirectlypredict
considered a “two force” member. It thus applies to the
in vivo performance. The results, however, can be used to
intervertebral device a resultant force directed along the
compare the varying degrees of subsidence between different
pushrod’s axes and located at the center of the superior
intervertebral body fusion device designs for a given density of
fixture’s sphere joint (the geometric center of the device being
simulated bone.
tested). The polyurethane blocks are to have surfaces that mate
5.4 The location within the simulated vertebral bodies and
geometrically with the intervertebral device similar to how the
positionoftheintervertebralbodyfusiondevicewithrespectto
device is intended to mate with vertebral end plates. The test
the loading axis will be dependent upon the design and
apparatus will be assembled such that the Z-axis of the
manufacturer’s recommendation for implant placement.
intervertebral device is initially coincident with the pushrod’s
axis and collinear with the axis of the testing machine’s
6. Apparatus
actuator and load cell. The length of the pushrod between the
6.1 Test machines will conform to the requirements of
center of the ball-and-socket joint to the center of the spherical
Practices E4.
surface is to be a minimum of 38 cm. This is required to
6.2 The intradiscal height, H, (Fig. 1) shall be determined
minimize deviation of the pushrod’s axis (direction of applied
from vertebral body and disc morphometric data at the in-
force, F) from that of the test machine’s load cell axis. In other
tended level of application. Suggested heights are as follows:
words, this is to minimize the error in using and reporting that
10 mm for the lumbar spine, 6 mm for the thoracic spine and
the force indicated by the load cell F is the a
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