ASTM F1820-22

Standard Test Method for Determining the Forces for Disassembly of Modular Acetabular Devices

SIGNIFICANCE AND USE
5.1 This test method is intended to assess the locking strength of the acetabular liner in a modular acetabular shell when subjected to three different force application conditions.  
5.2 This test method may not be appropriate for all implant applications. The user is cautioned to consider the appropriateness of the method in view of the materials and design being tested and their potential application.  
5.3 While these test methods may be used to measure the force required to disengage modular acetabular devices, comparison of such data for various device designs must take into consideration the size of the implant and the type of locking mechanism evaluated. The location of the locking mechanism relative to the load application may be dependent upon the size and design of the acetabular device. In addition, the locking mechanism itself may vary with size, particularly if the design is circumferential in nature (for example, a larger diameter implant would have a greater area of acetabular shell and liner interface than a small diameter implant).  
5.4 Material failure is possible before locking mechanism failure during either push-out or offset pull-out/lever-out conditions. This is due to the possibility that the shear strength of the material may be exceeded before the locking mechanism is fully tested.
SCOPE
1.1 This test method covers a standard methodology by which to measure the attachment strength between the modular acetabular shell and liner. Although the methodology described does not replicate physiological loading conditions, it has been described as a means of comparing the integrity of various locking mechanisms.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 14-Mar-2022
• ICS: 11.040.40 - Implants for surgery, prosthetics and orthotics
• Technical Committee: F04 - Medical and Surgical Materials and Devices
• Drafting Committee: F04.22 - Arthroplasty

Relations

• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014
• Refers: ASTM E4-10 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2010
• Refers: ASTM E4-09a - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Nov-2009
• Refers: ASTM E4-09 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Apr-2009
• Refers: ASTM F2345-03(2008) - Standard Test Methods for Determination of Static and Cyclic Fatigue Strength of Ceramic Modular Femoral Heads
• Effective Date: 15-Dec-2008
• Refers: ASTM E4-08 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Dec-2008
• Refers: ASTM E4-07 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jan-2007
• Refers: ASTM F2345-03 - Standard Test Methods for Determination of Static and Cyclic Fatigue Strength of Ceramic Modular Femoral Heads
• Effective Date: 01-Nov-2003
• Refers: ASTM E4-03 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 10-Aug-2003
• Refers: ASTM E4-02 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 10-Nov-2002
• Refers: ASTM E4-99 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 10-Apr-2001
• Refers: ASTM E4-01 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 10-Apr-2001

Overview

ASTM F1820-22 is the standard test method developed by ASTM International for determining the disassembly forces of modular acetabular devices. These devices are commonly used in orthopedic hip arthroplasty, consisting of an acetabular shell and a modular liner. The standard outlines a methodology to evaluate the attachment strength between these two components by subjecting them to specific mechanical test conditions. The purpose is to provide a comparative assessment of various liner locking mechanisms and inform design improvements, maintaining focus on patient safety and implant reliability.

Key Topics

• Three Test Conditions: ASTM F1820-22 specifies assessment of locking strength under axial (push-out), offset pull-out/lever-out, and torque-out disassembly conditions, each simulating different mechanical stresses encountered in clinical scenarios.
• Standardized Assessment: The test does not attempt to mimic physiological loading but serves as a repeatable method for comparing different modular acetabular device designs.
• Appropriateness of Test: The method may not be suitable for all implant designs or materials. Users must evaluate the method’s relevance based on the specific characteristics and intended application of the device being tested.
• Failure Modes: The standard acknowledges that material failure may occur before the locking mechanism fails, especially for certain liner materials, and provides guidance on reporting and minimizing these scenarios.
• Reporting Requirements: Results must include device specifics, measured disassembly forces or torques, details of test configurations, and failure modes, ensuring comprehensive data for evaluation and regulatory purposes.
• Environmental Factors: Variables such as temperature and test environment can impact results, particularly with specific polymers like ultra-high molecular weight polyethylene (UHMWPE).

Applications

ASTM F1820-22 is widely utilized by:

• Orthopedic Device Manufacturers: For comparative evaluation and quality assurance of modular hip acetabular designs before clinical use.
• Design and Development Teams: To refine locking mechanisms based on quantified performance, informing improvements for new or existing implant systems.
• Testing Laboratories: To provide third-party assessment and certification to regulatory bodies using a standardized, globally recognized methodology.
• Regulatory Compliance: To generate objective data supporting premarket submissions, demonstrating device safety and robustness to regulatory agencies.
• Device Comparison: For benchmarking against competitor products or historical designs, helping identify superior design features or avenues for improvement.

Practically, the standard enables medical stakeholders to make informed decisions regarding device selection, innovation, and approval, directly impacting patient safety and surgical outcomes by promoting durable, secure modular acetabular systems.

Related Standards

• ASTM E4: Practices for Force Calibration and Verification of Testing Machines
• ASTM F2345: Test Methods for Determination of Cyclic Fatigue Strength of Ceramic Modular Femoral Heads

Additional standards relevant to orthopedic implant testing include those addressing materials properties, surface characteristics, and wear testing. For optimal results, ASTM F1820-22 is often applied within a suite of complementary procedures to ensure comprehensive evaluation of hip prosthesis components.

Keywords: ASTM F1820-22, acetabular component, liner locking mechanism, arthroplasty, modular acetabular device, disassembly force, orthopedic implant testing, offset pull-out, torque disassembly, hip prosthesis standard.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F1820 − 22
Standard Test Method for
Determining the Forces for Disassembly of Modular
Acetabular Devices
This standard is issued under the fixed designation F1820; 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 3.1.1 acetabular liner—portion of the modular acetabular
device with an internal hemispherical socket intended to
1.1 This test method covers a standard methodology by
articulate with a femoral prosthesis. This can include acetabu-
which to measure the attachment strength between the modular
lar liners used for dual mobility or constrained applications.
acetabular shell and liner.Although the methodology described
The external geometry of this component interfaces with the
does not replicate physiological loading conditions, it has been
acetabular shell through a locking mechanism which may be
described as a means of comparing the integrity of various
integral to the design of the acetabular liner and shell or may
locking mechanisms.
rely upon additional components (for example, a metal ring or
1.2 The values stated in SI units are to be regarded as
screws).
standard. No other units of measurement are included in this
3.1.2 acetabular shell—the external, hollow (usually metal)
standard.
structure that provides additional mechanical support or rein-
1.3 This standard does not purport to address all of the
forcement for an acetabular liner and whose external features
safety concerns, if any, associated with its use. It is the
interface directly with the bones of the pelvic socket (for
responsibility of the user of this standard to establish appro-
example, through bone cement, intimate press-fit, coatings for
priate safety, health, and environmental practices and deter-
attachment to bone cement or tissue, integral screw threads,
mine the applicability of regulatory limitations prior to use.
anchoring screws, or pegs). The acetabular shell may be either
1.4 This international standard was developed in accor-
solid or contain holes for fixation, or contain a hole for
dance with internationally recognized principles on standard-
instrumentation.
ization established in the Decision on Principles for the
3.1.3 locking mechanism—any structure, design feature, or
Development of International Standards, Guides and Recom-
combination thereof that provides mechanical resistance to
mendations issued by the World Trade Organization Technical
movement between the acetabular liner and shell.
Barriers to Trade (TBT) Committee.
3.1.4 polar axis—the axis of revolution of the rotationally
symmetric portions of the acetabular liner or shell.
2. Referenced Documents
2.1 ASTM Standards:
4. Summary of Test Method
E4 Practices for Force Calibration and Verification of Test-
4.1 Axial Disassembly (Push-Out):
ing Machines
4.1.1 The axial disassembly test method of an acetabular
F2345 Test Methods for Determination of Cyclic Fatigue
liner and shell system provides a means to measure the axial
Strength of Ceramic Modular Femoral Heads
locking strength of the acetabular liner for modular acetabular
devices.
3. Terminology
4.2 Offset Pull-Out or Lever-Out Disassembly:
3.1 Definitions of Terms Specific to This Standard:
4.2.1 The offset pull-out or the lever-out disassembly
method is intended to assess the resistance of the locking
This test method is under the jurisdiction ofASTM Committee F04 on Medical
mechanism to edge forces that could occur when the neck of a
and Surgical Materials and Devices and is the direct responsibility of Subcommittee
hip prosthesis impinges on the edge of the acetabular liner.An
F04.22 on Arthroplasty.
impinging force could cause the edge of the acetabular liner
Current edition approved March 15, 2022. Published March 2022. Originally
opposite the area of impinging contact to be pushed out of the
approved in 1997. Last previous edition approved in 2013 as F1820 – 13. DOI:
10.1520/F1820-22.
acetabular shell. The resistance of the acetabular liner edge to
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
being pulled loose from the acetabular shell is a measure of the
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
resistance to impingement causing loosening of the acetabular
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. liner.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1820 − 22
4.3 Torque-Out Disassembly: the disassembly values. For statistical comparisons, the sample
4.3.1 The torque-out disassembly method is intended to size used for testing and comparison shall be justified. Pairing
assess the resistance of the locking mechanism to high-friction of the acetabular shells and liners shall be at random unless
events that would attempt to rotate the acetabular liner within otherwise reported. For tests with polyethylene acetabular
the acetabular shell. liners, the same set of five acetabular shells may be used for
each of the three tests provided that none of the acetabular
5. Significance and Use
shells is damaged by any of the preceding tests. Damage
includesanyfractureoftheacetabularshelloranydeformation
5.1 This test method is intended to assess the locking
which could affect the locking mechanism integrity.
strength of the acetabular liner in a modular acetabular shell
when subjected to three different force application conditions.
8. Procedure
5.2 This test method may not be appropriate for all implant
applications. The user is cautioned to consider the appropriate- 8.1 Assembly Procedure:
ness of the method in view of the materials and design being
8.1.1 The liner shall be assembled in the acetabular shell
tested and their potential application.
withapeakforceof2000 650N.Thelineofforceapplication
shall be coincident with the polar axis of the acetabular liner.
5.3 While these test methods may be used to measure the
The force may be applied with the appropriate surgical
force required to disengage modular acetabular devices, com-
instrument for the specific device, or a sphere of the same
parison of such data for various device designs must take into
diameter as the diameter of the articulating surface on the
consideration the size of the implant and the type of locking
acetabular liner. The following loading conditions are sug-
mechanism evaluated. The location of the locking mechanism
gested for assembly:
relative to the load application may be dependent upon the size
8.1.2 Forhard-bearingacetabularlinerswithataper-locking
and design of the acetabular device. In addition, the locking
mechanism, the force may be applied in displacement control
mechanism itself may vary with size, particularly if the design
at a rate of 0.04 mm/s or force control at a rate of 500 6
is circumferential in nature (for example, a larger diameter
100 N⁄s.
implant would have a greater area of acetabular shell and liner
interface than a small diameter implant). 8.1.3 For polyethylene acetabular liners, the force may be
applied in displacement control at a rate of 0.85 mm/s or force
5.4 Material failure is possible before locking mechanism
control at a rate of 500 6 100 N/s.
failure during either push-out or offset pull-out/lever-out con-
8.1.4 Alternatively, the assembly method specified by the
ditions. This is due to the possibility that the shear strength of
manufacturerintheappropriatesurgicaltechniquemaybeused
the material may be exceeded before the locking mechanism is
to assemble the acetabular liner in the acetabular shell. If this
fully tested.
method is used, it shall be reported and justified.
6. Apparatus
8.2 Axial Disassembly:
6.1 An apparatus capable of supporting only the acetabular
8.2.1 Once assembled, the acetabular liner and shell con-
shell while allowing the acetabular liner to be freely disas-
struct shall be placed in a solid fixture with continuous support
sembled from the acetabular shell is required.
of the acetabular shell as illustrated in Fig. 1. The fixture that
supports the acetabular shell shall do so without visual evi-
6.2 The testing machine shall conform to the requirements
dence of deformation during or after the test.
of Practices E4. The loads used to determine the attachment
8.2.2 An axial force shall be applied (coincident with the
strength shall be within the range of the testing machine as
defined in Practices E4. polar axis of the liner and shell) to the acetabular liner through
a center hole (polar axis of the acetabular shell) in the
6.3 The test machine shall be capable of delivering a
acetabular shell with a round rod at a rate no greater than
compressive or tensile force at a constant displacement rate.
0.04 mm⁄s for hard-bearing acetabular liners with a taper-
The test machine shall have a load monitoring and recording
locking mechanism or no greater than 0.85 mm/s for polyeth-
system.
ylene acetabular liners. If a faster rate is used for hard-bearing
liners, it shall be demonstrated that this does not affect the test
7. Sampling
results.
7.1 All acetabular liners shall be representative of implant
8.2.3 The direction of force application and rod longitudinal
quality products. This shall include any sterilization or thermal
axis shall be collinear to the polar axis of the acetabular liner
processes which may alter the material properties or geometry.
andshelltowithin2°,andthecenteroftherodcontactwiththe
7.2 Apartially finished acetabular shell or permanent fixture
acetabular liner shall be less than 2 mm from the polar axis of
block may be substituted for a completed acetabular shell
the acetabular liner.
provided that the internal materials, finish, locking mechanism,
8.2.4 Asmall diameter drill blank or rod could be used as a
geometry, and manufacturing conditions are identical to the
force applicator. The rod shall not be less than 5 mm in
actual acetabular shell.
diameter. If the rod diameter is too small, it may punch a hole
7.3 Aminimum of five acetabular shell and liner assemblies in the acetabular liner during the test. The drill blank or rod
shall be tested in each of the three test methods (axial, offset shall be stiff enough that it does not buckle under the test
pull-out or lever-out, and torque-out disassembly) to determine forces, and there shall be sufficient clearance between any hole
F1820 − 22
FIG. 1 Schematic of Axial Acetabular Liner Disassembly
in the acetabular shell and the drill blank or rod such that there 8.3.1 Prior to assembly, the acetabular liner shall have a
would be no contact between the hole and the drill blank or rod rectangular slot cut or hole drilled into one side of the interior
during the test.
surface of the acetabular liner to use as the force application
point for the test. Suggested slot dimensions of at least 8 mm
NOTE 1—It may be necessary to create a hole in the acetabular shell at
long and 4 mm wide may be used. The slot shall have the long
the apex to apply an axial force to the acetabular liner.
axis aligned roughly perpendicular to the load axis. The hole
8.2.5 The maximum force required to completely disengage
should be 4 to 6 mm in diameter. It is recommended that the
the acetabular liner from the acetabular shell shall be measured
slot or hole be approximately perpendicular to the polar axis. It
and recorded.
is recommended that the depth of the slot or hole not exceed
8.2.6 The testing of any individual specimen shall be
50 % of the acetabular liner thickness at the location of the slot
terminated when one of the following has occurred.
or hole. The top edge of the slot or hole (h in Fig. 2) shall be
8.2.6.1 The disengagement force becomes negligible.
approximately 80 % of the depth of the acetabular liner (the
8.2.6.2 Prior to disassembly, the acetabular liner suffers
distance along the polar axis of the acetabular liner from the
excessive damage (that is, complete fracture of a portion of the
poleoftheacetabularlinertotheplaneofthetopsurfaceofthe
acetabular liner or severe acetabular liner deformation). Such
acetabular liner (h in Fig. 2)) and should not interfere with the
occurrences shall invalidate the test.
locking mechanism.
8.2.7 For tests with thin polyethylene acetabular liners, the
rod applying the force could puncture the acetabular liner 8.3.2 Alternatively,forhard-bearingacetabularlinersitmay
without locking mechanism failure. If this occurs, additional be necessary to adhesively bond a metal washer to the interior
testing shall be required. It may be necessary to increase the surface of the liner to use as the force application point for the
cross-sectional area of the rod and make it conform to the
test. The location of the hole in the washer shall meet the
contacted portion of the acetabular shell such that material requirements for the hole location in 8.3.1.
failure does not occur. After additional reported attempts to
8.3.3 Once assembled, the acetabular liner and shell assem-
perform the axial disassembly test, material failure of the
bly shall be placed in a fixture similar to that illustrated in Fig.
acetabular liner may still occur without locking mechanism
2. The acetabular shell shall be constrained during testing such
failure. If failure of the locking mechanism is not achieved
thatitisnotdeformed.Thiscanbeaccomplishedbysupporting
during additional testing, justification of the results shall be
the exterior bottom of the acetabular shell on a flat plate and
provided.
constraining it against the plate by applying even pressure to
8.3 Offset Pull-Out or Lever-Out Disassembly: the circumference of the acetabular shell. Alternatively, the
F1820 − 22
FIG. 2 Schematic of Offset Pull-Out Disassembly
acetabular shell may be constrained by embedding it in epoxy a faster rate is used for hard-bearing liners, it shall be
or cast resin. The embedding material shall be sufficiently demonstrated that this does not affect the test results.
strong that it does not fail or disengage before the acetabular 8.3.5 For the lever-out method (Fig. 3), a lever arm with an
liner locking mechanism. offset that will reach into the acetabular shell and fit into the
8.3.4 For the offset pull-out method (Fig. 2), the force shall slot or hole as shown in Fig. 3 shall be set up with the top
be applied with a straight bar with a feature to attach to the surface of the lever arm parallel to the top surface of the
prepared attachment point in the acetabular liner. The line of acetabular liner. The lever shall be in line with a diameter on
action of the applied force to the bar shall be constrained to a thetopsurfaceoftheshell.Afulcrumpointorpivotshallbeset
direction that is parallel to polar axis of the liner. A method at a distance L from the lever contact point with the liner. The
such as the bearing constraint illustrated in Fig. 2 is needed to fulcrumpointshouldbeadjacentto,butnotincontactwith,the
keep the force directed in the axis parallel to the polar axis, liner.Aforceshallbeappliedtotheacetabularlineratthepoint
becausedisengagingsomelinerdesignscouldgenerateoff-axis of contact with the lever arm at a constant rate no greater than
forces.Aforce shall be applied to the acetabular liner at a rate 0.04 mm/s for hard-bearing acetabular liners or no greater than
no greater than 0.04 mm/s for hard-bearing acetabular liners or 0.85 mm/s for polyethylene acetabular liners. The rate of the
no greater than 0.85 mm/s for polyethylene acetabular liners. If test frame actuator must
...

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: F1820 − 13 F1820 − 22
Standard Test Method for
Determining the Forces for Disassembly of Modular
Acetabular Devices
This standard is issued under the fixed designation F1820; 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 test method covers a standard methodology by which to measure the attachment strength between the modular acetabular
shell and liner. Although the methodology described does not replicate physiological loading conditions, it has been described as
a means of comparing the integrity of various locking mechanisms.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E4 Practices for Force Calibration and Verification of Testing Machines
F2345 Test Methods for Determination of Cyclic Fatigue Strength of Ceramic Modular Femoral Heads
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 acetabular liner—portion of the modular acetabular device with an internal hemispherical socket intended to articulate with
the head of a femoral prosthesis. This can include acetabular liners used for dual mobility or constrained applications. The external
geometry of this component interfaces with the acetabular shell through a locking mechanism which may be integral to the design
of the acetabular liner and shell or may rely upon additional components (for example, metal ring, screws, and so forth).a metal
ring or screws).
3.1.2 acetabular shell—the external, hollow (usually metal) structure that provides additional mechanical support or reinforcement
for an acetabular liner and whose external features interface directly with the bones of the pelvic socket (for example, through bone
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
F04.22 on Arthroplasty.
Current edition approved Feb. 1, 2013March 15, 2022. Published March 2013March 2022. Originally approved in 1997. Last previous edition approved in 20092013 as
F1820 – 97F1820 – 13.(2009). DOI: 10.1520/F1820-13.10.1520/F1820-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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
F1820 − 22
cement, intimate press-fit, porous ingrowth, coatings for attachment to bone cement or tissue, integral screw threads, anchoring
screws, pegs, and so forth). or pegs). The acetabular shell may be either solid or contain holes for fixation, or contain a hole for
instrumentation, or all of these.instrumentation.
3.1.3 locking mechanism—any structure, design feature, or combination thereof,thereof that provides mechanical resistance to
movement between the acetabular liner and shell.
3.1.4 polar axis—the axis of revolution of the rotationally symmetric portions of the acetabular liner or shell.
4. Summary of Test Method
4.1 All acetabular liners shall be inserted into the acetabular shells for testing by applying a force of 2 kN. This value is similar
to the force required to set the head in Test Methods F2345.
4.1 Axial Disassembly: Disassembly (Push-Out):
4.1.1 The axial disassembly test method of an acetabular device test method liner and shell system provides a means to measure
the axial locking strength of the acetabular liner for modular acetabular devices.
4.2.2 Following proper assembly of the acetabular liner in an acetabular shell, the assembled device is attached to a fixture such
that the cup opening is facing downward. The acetabular shell is supported and an axial force is applied to the acetabular liner until
it disengages. The force required to disengage the acetabular liner from the acetabular shell is recorded.
4.2 Offset PulloutPull-Out or Lever Out Lever-Out Disassembly:
4.2.1 The offset pulloutpull-out or the lever out lever-out disassembly method is intended to assess the resistance of the locking
mechanism to edge forces that could occur when the neck of a hip prosthesis impinges on the edge of the acetabular liner. An
impinging force could cause the edge of the acetabular liner opposite the area of impinging contact to be pushed out of the
acetabular shell. The resistance of the acetabular liner edge to being pulled loose from the acetabular shell is a measure of the
resistance to impingement causing loosening of the acetabular liner.
4.3.2 Following proper assembly of the acetabular liner in an acetabular shell, the assembled device is attached to a fixture such
that the cup opening is facing upward. The acetabular shell is constrained from moving at a minimum of four locations spaced
uniformly around the top circumference of the acetabular shell. For an offset pullout a force is applied to a liner contact point, a
location near the top surface of the liner. The line of action of the force is constrained to a direction that is parallel to polar axis
of the liner. The force required to disengage the acetabular liner from the acetabular shell is recorded.
4.3.3 For a lever out test, the force is applied through a lever mechanism with a liner contact point near the top surface of the liner
and a fulcrum that is outside the liner and directly opposite the contact point. The centerline of the lever shall intersect the polar
axis of the liner. The force required to disengage the acetabular liner from the acetabular shell shall be recorded. The distances
between the applied force and the fulcrum and the resultant force and the fulcrum are recorded. These values are used to calculate
the lever-out force.
F1820 − 22
4.3 Torque Out Torque-Out Disassembly:
4.3.1 The torque out torque-out disassembly method is intended to assess the resistance of the locking mechanism to high friction
high-friction events that would attempt to rotate the acetabular liner within the acetabular shell.
4.4.2 Following proper assembly of the acetabular liner in an acetabular shell, the assembled device is attached to a fixture such
that the shell opening is unimpeded, allowing the acetabular liner to be pushed free of the shell. The acetabular shell is constrained
from moving at a minimum of four locations spaced uniformly around the top circumference of the acetabular shell. A head of a
diameter appropriate to the liner is attached to the liner at a minimum of four equally spaced locations or adhesively bonded. A
torque is applied through the head along the polar axis of the liner. The torque required to disengage the acetabular liner from the
acetabular shell or break the adhesive bond between the articulating surfaces of the acetabular liner and the head is recorded.
5. Significance and Use
5.1 This test method is intended to help assess the locking strength of the acetabular liner in a modular acetabular shell when
subjected to three different force application conditions.
5.2 This test method may not be appropriate for all implant applications. The user is cautioned to consider the appropriateness of
the method in view of the materials and design being tested and their potential application.
5.3 While these test methods may be used to measure the force required to disengage modular acetabular devices, comparison of
such data for various device designs must take into consideration the size of the implant and the type of locking mechanism
evaluated. The location of the locking mechanism relative to the load application may be dependent upon the size and design of
the acetabular device. In addition, the locking mechanism itself may vary with size, particularly if the design is circumferential
in nature (for example, a larger diameter implantsimplant would have a greater area of acetabular shell/acetabular shell and liner
interface than a small diameter implant).
5.4 Material failure is possible before locking mechanism failure during either push-out or offset pullout/lever-outpull-out/lever-
out conditions. This is due to the possibility that the shear strength of the material may be exceeded before the locking mechanism
is fully tested. If this occurs, those results shall be reported and steps taken to minimize this effect. Some possibilities for
minimizing shear might include utilizing the smallest size components, using a flat rod end rather than a round rod end or placing
a small metal plate between the liner and shell (during push-out). For well-designed polyethylene inserts, it may not be possible
to push out or offset pullout/lever out the liner without fracture. In some cases, reporting the maximum force and acknowledging
that the true disassembly force will be higher may be justified.
6. Apparatus
6.1 An apparatus capable of supporting only the acetabular shell while allowing the acetabular liner to be freely disassembled from
the acetabular shell is required.
6.2 The testing machine shall conform to the requirements of Practices E4. The loads used to determine the attachment strength
shall be within the range of the testing machine as defined in Practices E4.
6.3 The test machine shall be capable of delivering a compressive or tensile force at a constant displacement rate. The test machine
shall have a load monitoring and recording system.
7. Sampling
7.1 All acetabular liners shall be representative of implant quality products. This shall include any sterilization or thermal
processes which may alter the material properties or geometry.
7.2 A partially finished acetabular shell or permanent fixture block may be substituted for a completed acetabular shell provided
that the internal materials, finish, locking mechanism, geometry, and geometry manufacturing conditions are identical to the actual
acetabular shell.
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7.3 A minimum of five acetabular shell and liner assemblies shall be tested in each of the three tests test methods (axial, offset
pulloutpull-out or lever-out, and torque-out disassembly) to determine the disassembly values. For statistical comparisons, the
sample size used for testing and comparison shall be justified. Pairing of the acetabular shells and liners shall be at random unless
otherwise reported. For tests with polyethylene acetabular liners, the same set of five acetabular shells may be used for each of
the three tests provided that none of the acetabular shells areis damaged by any of the preceding tests. Damage includes any
fracture of the acetabular shell or any deformation which could affect the locking mechanism integrity.
8. Procedure
8.1 Assembly Procedure:
8.1.1 The liner shall be assembled in the acetabular shell with a peak force of 2 kN 2000 6 50 N. The force shall be applied in
displacement control at a rate of 0.04 mm/s or force control at a rate of 1 kN/s or less. The line of force application shall be
coincident with the polar axis of the acetabular liner. The force may be applied with the appropriate surgical instrument for the
specific device, or a sphere of the same diameter as the diameter of the articulating surface on the liner.acetabular liner. The
following loading conditions are suggested for assembly:
8.1.2 For hard-bearing acetabular liners with a taper-locking mechanism, the force may be applied in displacement control at a
rate of 0.04 mm/s or force control at a rate of 500 6 100 N ⁄s.
8.1.3 For polyethylene acetabular liners, the force may be applied in displacement control at a rate of 0.85 mm/s or force control
at a rate of 500 6 100 N/s.
8.1.4 Alternatively, the assembly method specified by the manufacturer in the appropriate surgical technique may be used to
assemble the acetabular liner in the acetabular shell. If this method is used, it shall be reported and justified.
8.2 Axial Disassembly:
8.2.1 Once assembled, the acetabular liner and shell construct shall be placed in a solid fixture with continuous support of the
acetabular shell as illustrated in Fig. 1. The fixture that supports the acetabular shell shall do so without visual evidence of
deformation during or after the test.
8.2.2 An axial force shall be applied (coincident with the polar axis of the liner and shell) to the acetabular liner through a center
hole (polar axis of the acetabular shell) in the acetabular shell with a round rod at a rate no greater than 0.04 mm ⁄s for hard-bearing
acetabular liners with a taper-locking mechanism or no greater than 0.85 mm/s for polyethylene acetabular liners. If a faster rate
is used for hard-bearing liners, it shall be demonstrated that this does not affect the test results.
8.2.3 The direction of force application and rod longitudinal axis shall be collinear to the polar axis of the acetabular liner and
shell to within 2°, and the center of the rod contact with the acetabular liner shall be less than 2 mm from the polar axis of the
acetabular liner.
8.2.4 Once assembled, the liner shell construct shall be placed in a solid metallic fixture with continuous support of the shell as
illustrated in Fig. 1. The fixture that supports the acetabular shell shall do so without visual evidence of deformation during or after
the test. An axial force shall be applied (coincident with the polar axes of the liner and shell) to the liner through a center hole
(polar axis of the acetabular shell) in the shell at a rate of 5.1 cm/min with a round rod. The direction of force application and rod
longitudinal axis shall be collinear to the polar axes of the liner and shell to within 2°; and the center of the rod contact with the
liner shall be less than 2 mm from the polar axis of the liner. It may be necessary to create a hole in the shell at the apex in order
to apply an axial force to the liner. A small diameter drill blank or rod could be used as a force applicator. The rod diameter shall
not be less than 5 mm in diameter. If the rod diameter is too small, it may punch a hole in the acetabular liner during the test. The
drill blank or rod shall be stiff enough that it does not buckle under the test forces, and there shall be sufficient clearance between
any hole in the acetabular shell and the drill blank or rod such that there would be no contact between the hole and the drill blank
or rod during the test. The maximum force required to completely disengage the liner from the shell should be measured and
recorded.
NOTE 1—It may be necessary to create a hole in the acetabular shell at the apex to apply an axial force to the acetabular liner.
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FIG. 1 Schematic of Axial Acetabular Liner Disassembly
8.2.5 Record the maximum disassembly force.The maximum force required to completely disengage the acetabular liner from the
acetabular shell shall be measured and recorded.
8.2.6 The testing of any individual samplespecimen shall be terminated when one of the following has occurred.
8.2.6.1 The disengagement force becomes negligible.
8.2.6.2 Prior to disassembly, the acetabular liner suffers excessive damage (that is, complete fracture of a portion of the acetabular
liner or severe acetabular liner deformation). Such occurrences shall be considered an invalid invalidate the test.
8.2.7 For tests with thin polyethylene acetabular liners, the rod applying the force could actually puncture the liner. If this occurs
it may be advisableacetabular liner without locking mechanism failure. If this occurs, additional testing shall be required. It may
be necessary to increase the cross-sectional area of the rod. If puncture still occurs, it may be possible to justify the punctured liners
as valid tests, if the liner is thin and the liner locking mechanism is strong.rod and make it conform to the contacted portion of
the acetabular shell such that material failure does not occur. After additional reported attempts to perform the axial disassembly
test, material failure of the acetabular liner may still occur without locking mechanism failure. If failure of the locking mechanism
is not achieved during additional testing, justification of the results shall be provided.
8.3 Offset PulloutPull-Out or Lever Out Lever-Out Disassembly:
8.3.1 Prior to assembly, the acetabular liner shall have a rectangular slot cut or hole drilled into one side of the interior surface
of the acetabular liner to use as the force application point for the test. TheSuggested slot shall bedimensions of at least 8 mm long
and 4 mm wide. wide may be used. The slot shall have the long axis aligned roughly perpendicular to the load axis. The hole should
be 4 to 6 mm in diameter. The It is recommended that the slot or hole should be approximately perpendicular to the polar axis.
The It is recommended that the depth of the slot or hole shall not exceed 50 % of the acetabular liner thickness at the location of
the slot. slot or hole. The top edge of the slot or hole, h1hole (h in Fig. 2) shall be approximately 80 % of the depth of the liner
(h) (that is, the acetabular liner (the distance along the polar axis of the acetabular liner from the pole of the acetabular liner to
the plane of the top surface of the liner) acetabular liner (h in Fig. 2)) and should not interfere with the locking mechanism.
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FIG. 2 Schematic of Offset PulloutPull-Out Disassembly
8.3.2 Alternatively, for hard-bearing acetabular liners it may be possiblenecessary to adhesively bond a metal washer to the interior
surface of the liner to use as the force application point for the test. The location of the hole in the washer shall meet the same
requirements for the hole location in 8.3.1. With ceramic liners, it may be necessary to adhesively bond a metal head into the liner
to perform this test.
8.3.2.1 The surfaces of the ceramic liner and the head must be roughened to improve the adhesive bond.
8.3.2.2 The head shall have internal surfaces machined so that the force application point is at the appropriate height location on
the liner noted in 8.3.1 and the tip of the force application point is within 1 mm of the liner articulating surface.
8.3.3 Once assembled, the acetabular liner and shell assembly shall be placed in a fixture similar to that illustrated in Fig. 2 and
Fig. 3. The exterior bottom will be supported acetabular shell shall be constrained during testing such that it is not deformed. This
can be accomplished by supporting the exterior bottom of the acetabular shell on a flat plate and the shell shall be constrained
tightly constraining it against the plate at a minimum of four locations spaced evenly around the edge of the shell. The top surface
of the shell shall be parallel to the plate. The force of the constraint shall not be high enough to deform the shell.by applying even
FIG. 3 Schematic of Lever Out DisassemblyLever-Out Disassembly with Acetabular Liner Hole
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pressure to the circumference of the acetabu
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