ASTM F2502-17

Standard Specification and Test Methods for Absorbable Plates and Screws for Internal Fixation Implants

SIGNIFICANCE AND USE
4.1 Absorbable devices are intended to degrade and absorb over time once they are implanted into the body. This makes a removal operation unnecessary, which is especially advantageous for pediatric patients.  
4.2 While the polymer degrades due to hydrolytic reaction with the environment, the mechanical performance of the device also deteriorates. The key to developing mechanically effective fracture fixation systems based on absorbable devices is to provide an adequate level of fixation strength and stiffness for a time frame that exceeds that expected for fracture healing. Once the fracture is healed, the device can be completely absorbed by the body. The biological performance of the device, particularly for application at a bony site, may be enhanced by incorporation of bioactive fillers in the polymer.  
4.3 Absorbable devices will be tested using test methods that are similar to those used to evaluate conventional metallic devices. The pre-test conditioning requirements, handling requirements, and time-dependent mechanical property evaluations for absorbable devices shall be considered.  
4.4 This specification and accompanying test methods are intended to complement the more general considerations for the assessment of absorbable polymeric implants that are described within Guide F2902.
FIG. 1 Screw Parameters
SCOPE
1.1 This specification and test methods cover the mechanical characterization of plates and screws for orthopedic internal fixation. Covered devices are fabricated from one or more hydrolytically degradable polymer (from this point on referred to as “absorbable”) resins or resin composites.  
1.2 This specification establishes a common terminology to describe the size and other physical characteristics of absorbable implants and performance definitions related to the performance of absorbable devices.  
1.3 This specification establishes standard test methods to consistently measure performance-related mechanical characteristics of absorbable devices when tested under defined conditions of pretreatment, temperature, humidity, and testing machine speed.  
1.4 This specification may not be appropriate for all absorbable devices, especially those that possess limited hydrolytic susceptibility and degrade in vivo primarily through enzymatic action. The user is cautioned to consider the appropriateness of the standard in view of the particular absorbable device and its potential application.  
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.6 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.  
1.7 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: 31-Aug-2017
• ICS: 11.040.40 - Implants for surgery, prosthetics and orthotics
• Technical Committee: F04 - Medical and Surgical Materials and Devices
• Drafting Committee: F04.21 - Osteosynthesis

Relations

• Replaces: ASTM F2502-11 - Standard Specification and Test Methods for Absorbable Plates and Screws for Internal Fixation Implants
• Effective Date: 01-Sep-2017
• Refers: ASTM E1823-24a - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Feb-2024
• Refers: ASTM E1823-24 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2024
• Refers: ASTM F2503-23e1 - Standard Practice for Marking Medical Devices and Other Items for Safety in the Magnetic Resonance Environment
• Effective Date: 01-Apr-2023
• Refers: ASTM E1823-20 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2020
• Refers: ASTM F2313-18 - Standard Specification for Poly(glycolide) and Poly(glycolide-co-lactide) Resins for Surgical Implants with Mole Fractions Greater Than or Equal to 70 % Glycolide
• Effective Date: 15-Dec-2018
• Refers: ASTM F2579-18 - Standard Specification for Amorphous Poly(lactide) and Poly(lactide-co-glycolide) Resins for Surgical Implants
• Effective Date: 15-Dec-2018
• Refers: ASTM D790-17 - Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• Effective Date: 01-Jul-2017
• Refers: ASTM F2902-16 - Standard Guide for Assessment of Absorbable Polymeric Implants
• Effective Date: 01-Dec-2016
• Refers: ASTM F2902-16e1 - Standard Guide for Assessment of Absorbable Polymeric Implants
• Effective Date: 01-Dec-2016
• Refers: ASTM F1635-16 - Standard Test Method for <emph type="bdit">in vitro</emph> Degradation Testing of Hydrolytically Degradable Polymer Resins and Fabricated Forms for Surgical Implants
• Effective Date: 01-Dec-2016
• Refers: ASTM D790-15 - Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• Effective Date: 01-Dec-2015
• Refers: ASTM D790-15e1 - Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• Effective Date: 01-Dec-2015
• Refers: ASTM F382-14 - Standard Specification and Test Method for Metallic Bone Plates
• Effective Date: 01-Nov-2014
• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014

Overview

ASTM F2502-17 is the internationally recognized standard specification and test methods for absorbable plates and screws used in internal fixation implants. Developed by ASTM International’s Committee F04 on Medical and Surgical Materials and Devices, this standard sets out the requirements for mechanical characterization, testing, and performance assessment of orthopedic implants made from hydrolytically degradable (absorbable) polymer resins or resin composites.

This standard plays a vital role in ensuring that absorbable internal fixation devices are safe, effective, and able to provide the necessary strength and support during the critical fracture healing period. Once healing is complete, these devices degrade harmlessly within the body, eliminating the need for surgical removal-an advantage particularly significant for pediatric patients.

Key Topics

ASTM F2502-17 covers several critical aspects necessary for the development, validation, and implementation of absorbable plates and screws in clinical practice:

• Material Requirements: Defines allowable compositions such as polylactide, polyglycolide, and related bioabsorbable polymers.
• Terminology: Establishes a common language for device size, geometry, and performance characteristics.
• Mechanical Testing: Details standardized test methods for evaluating mechanical properties, including:
  • Offset yield strength
  • Torsional strength and driving torque
  • Axial pullout strength
  • Bending properties for bone plates
• Performance Considerations: Emphasizes maintaining sufficient strength and stiffness over a period that exceeds expected healing times, before controlled degradation occurs.
• Sample Handling and Conditioning: Specifies sample preparation, conditioning intervals, and test environments (e.g., physiologic temperature and pH).
• Reporting Requirements: Outlines detailed reporting protocols for test results to ensure consistency and reproducibility.
• Health and Safety: Reminds users to follow relevant safety and regulatory practices when applying this standard.

Applications

The practical benefits and applications of ASTM F2502-17 are broad, especially in the realms of orthopedic surgery and medical device manufacturing:

• Orthopedic Internal Fixation: Used to guide the design and assessment of absorbable plates and screws deployed in the stabilization of bone fractures.
• Pediatric Orthopedics: Especially valuable for young patients as the absorbable nature of these implants removes the need for secondary removal surgeries, reducing risk and trauma.
• Product Development: Enables manufacturers to develop and validate new absorbable implant systems that meet consistent mechanical performance and safety requirements.
• Quality Assurance: Provides standardized test methods for ensuring that production lots conform to design specifications and performance criteria.
• Regulatory Approval: Supports submissions to regulatory authorities by supplying a widely adopted framework for implant testing and performance documentation.
• Clinical Research: Serves as a reference for clinical trials evaluating the durability and safety of new absorbable fixation devices.

Related Standards

ASTM F2502-17 references or complements several other national and international standards to ensure comprehensive evaluation of absorbable implants. Key related standards include:

• ASTM F2902: Guide for assessment of absorbable polymeric implants
• ASTM F382 & F543: Specifications and test methods for metallic bone plates and screws
• ASTM F1635: In vitro degradation testing of hydrolytically degradable polymer resins
• ISO 13781 & ISO 15814: In vitro degradation testing for polylactide-based polymers and copolymers
• ISO 14630: General requirements for non-active surgical implants

These references help harmonize global practices for material characterization and performance evaluation, strengthening patient outcomes and device reliability in the field of bioabsorbable orthopedic implants.

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Keywords: ASTM F2502-17, absorbable plates and screws, internal fixation, orthopedic implants, mechanical testing, biodegradable implants, hydrolytically degradable polymers, pediatric orthopedics, implant standards, test methods, quality assurance.

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:F2502 −17
Standard Specification and Test Methods for
Absorbable Plates and Screws for Internal Fixation
Implants
This standard is issued under the fixed designation F2502; 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
1.1 This specification and test methods cover the mechani- 2.1 ASTM Standards:
calcharacterizationofplatesandscrewsfororthopedicinternal D790 Test Methods for Flexural Properties of Unreinforced
fixation. Covered devices are fabricated from one or more and Reinforced Plastics and Electrical Insulating Materi-
hydrolytically degradable polymer (from this point on referred als
to as “absorbable”) resins or resin composites. E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
1.2 This specification establishes a common terminology to
E122 Practice for Calculating Sample Size to Estimate,With
describe the size and other physical characteristics of absorb-
Specified Precision, the Average for a Characteristic of a
able implants and performance definitions related to the
Lot or Process
performance of absorbable devices.
E1823 TerminologyRelatingtoFatigueandFractureTesting
1.3 This specification establishes standard test methods to
F116 Specification for Medical Screwdriver Bits
consistently measure performance-related mechanical charac-
F382 SpecificationandTestMethodforMetallicBonePlates
teristics of absorbable devices when tested under defined
F543 Specification and Test Methods for Metallic Medical
conditions of pretreatment, temperature, humidity, and testing
Bone Screws
machine speed.
F565 PracticeforCareandHandlingofOrthopedicImplants
1.4 This specification may not be appropriate for all absorb- and Instruments
F1088 Specification for Beta-Tricalcium Phosphate for Sur-
able devices, especially those that possess limited hydrolytic
susceptibility and degrade in vivo primarily through enzymatic gical Implantation
F1185 Specification for Composition of Hydroxylapatite for
action.The user is cautioned to consider the appropriateness of
Surgical Implants
the standard in view of the particular absorbable device and its
potential application. F1635 Test Method for in vitro Degradation Testing of
HydrolyticallyDegradablePolymerResinsandFabricated
1.5 The values stated in SI units are to be regarded as
Forms for Surgical Implants
standard. No other units of measurement are included in this
F1839 Specification for Rigid Polyurethane Foam for Use as
standard.
a Standard Material for Testing Orthopaedic Devices and
1.6 This standard does not purport to address all of the
Instruments
safety concerns, if any, associated with its use. It is the
F1925 SpecificationforSemi-CrystallinePoly(lactide)Poly-
responsibility of the user of this standard to establish appro-
mer and Copolymer Resins for Surgical Implants
priate safety, health and environmental practices and deter-
F2313 Specification for Poly(glycolide) and Poly(glycolide-
mine the applicability of regulatory limitations prior to use.
co-lactide) Resins for Surgical Implants with Mole Frac-
1.7 This international standard was developed in accor-
tions Greater Than or Equal to 70 % Glycolide
dance with internationally recognized principles on standard-
F2503 Practice for Marking Medical Devices and Other
ization established in the Decision on Principles for the
Items for Safety in the Magnetic Resonance Environment
Development of International Standards, Guides and Recom-
F2579 Specification for Amorphous Poly(lactide) and
mendations issued by the World Trade Organization Technical
Poly(lactide-co-glycolide) Resins for Surgical Implants
Barriers to Trade (TBT) Committee.
F2902 Guide for Assessment of Absorbable Polymeric Im-
plants
This specification and test methods is under the jurisdiction of ASTM
Committee F04 on Medical and Surgical Materials and Devices and is the direct
responsibility of Subcommittee F04.21 on Osteosynthesis. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Sept. 1, 2017. Published October 2017. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2005. Last previous edition approved in 2011 as F2502 – 11. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/F2502-17. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2502−17
F3160 Guide for Metallurgical Characterization of Absorb- 4.2 While the polymer degrades due to hydrolytic reaction
able Metallic Materials for Medical Implants with the environment, the mechanical performance of the
device also deteriorates. The key to developing mechanically
2.2 ISO Standards:
effective fracture fixation systems based on absorbable devices
ISO 13781 Poly (L-Lactide) Resins and Fabricated Forms
is to provide an adequate level of fixation strength and stiffness
for Surgical Implants—In Vitro Degradation Testing
foratimeframethatexceedsthatexpectedforfracturehealing.
ISO 14630 Non-Active Surgical Implants—General Re-
Once the fracture is healed, the device can be completely
quirements
absorbed by the body. The biological performance of the
ISO 15814 Copolymers and Blends Based on
device, particularly for application at a bony site, may be
Polylactide—In Vitro Degradation Testing
enhanced by incorporation of bioactive fillers in the polymer.
3. Terminology
4.3 Absorbable devices will be tested using test methods
3.1 Definitions:
that are similar to those used to evaluate conventional metallic
3.1.1 Unless otherwise defined in this specification, the
devices. The pre-test conditioning requirements, handling
terminology related to mechanical testing that is used in these
requirements, and time-dependent mechanical property evalu-
test methods will be in accordance with the definitions of
ations for absorbable devices shall be considered.
Terminologies E6 and E1823, and Specifications F382 and
4.4 This specification and accompanying test methods are
F543.
intended to complement the more general considerations for
3.2 General Definitions:
the assessment of absorbable polymeric implants that are
3.2.1 absorbable, adj—in the body, referring to an initially
described within Guide F2902.
distinct foreign material or substance that either directly or
through intended degradation can pass through or be assimi-
5. Materials and Manufacture
lated by cells and/or tissue.
5.1 Absorbable devices may be fabricated from one of the
NOTE 1—See Appendix X1.5 for a discussion regarding the usage of following materials:
“absorbable” and other related terms.
5.1.1 L-lactide, D-lactide, D, L-lactide, glycolide, or other
3.2.2 absorbable composite—an absorbable polymer resin known hydrolytically degradable polymer resins or copoly-
mers. (for additional information, see complementary test
orconstructincorporatingaparticulateand/orfibrousbioactive
methods found in ISO 13781, ISO 15814, and F1635, and in
and/or absorbable filler material.
related Specifications F1925, F2313, and F2579.)
3.2.3 bone anchor—a device or a component of a device
5.1.2 Other absorbable polymeric, ceramic, or metallic
that provides the attachment to the bone.
based constructs that degrade through non-hydrolytic means,
3.2.4 bone plate—a device, when affixed with screws or
suchasthosedescribedinSpecificationsF1088andF1185,and
cerclage wire, intended to provide alignment of two or more
Guide F3160 may be considered, but precautions should be
bone sections, primarily by spanning the fracture or defect. A
undertaken to assure a materials-appropriate degradation envi-
bone plate has two or more holes. Its width and thickness
ronment is maintained.
usually are not the same in magnitude.
5.2 The manufacturer shall ensure that materials used to
3.2.5 deterioration—the reduction or worsening of me-
manufacture absorbable implants are suitable for implanting
chanical or other functional performance properties of a
into the body. Methods to evaluate a material’s suitability are
device.
described in ISO 14630.
3.2.6 hydrolytically degradable polymer—any polymeric
5.3 All absorbable devices made of materials that have an
material in which the primary mechanism of chemical degra-
ASTM committee F04 or D20 standard designation or an ISO
dation in the body is by hydrolysis (water reacting with the
designation shall meet those requirements given in the ASTM
polymer resulting in cleavage of the chain).
standards.
3.2.7 suture anchor—a device that provides a means to
6. General Requirements and Performance
attach soft tissue to bone with a suture.
Considerations
3.3 Definitions of Terms Specific to This Standard:
6.1 Absorbable Bone Screws—The following properties
3.3.1 insertion depth (mm)—the linear advancement of a
may be important when determining the suitability of a screw
device into the test block measured relative to its seated
position at the test block’s surface prior to testing.
4. Significance and Use
4.1 Absorbable devices are intended to degrade and absorb
over time once they are implanted into the body. This makes a
removal operation unnecessary, which is especially advanta-
geous for pediatric patients.
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. FIG. 1Screw Parameters
F2502−17
for a particular application. However, the test methods refer- 7.1.2.1 Other physiologic relevant solutions may be substi-
enced as follows may not be appropriate for all types of tuted provided the solution is properly buffered. An anti-
implant applications. The user is cautioned to consider the microbial additive should be used to inhibit the growth of
appropriateness of the test methods in view of the devices microorganisms in the solution during the test period. The
being tested and their potential application. investigator shall demonstrate that the chosen antimicrobial
6.1.1 Offset Yield Strength is the stress at which the stress- does not affect the absorption rate (see X1.3).
strain curve departs from linearity by a specified percent of 7.1.3 Constant Temperature Bath or Oven—An aqueous
deformation (offset). bath or heated air oven capable of maintaining the samples and
6.1.2 Torsional Strength is an important parameter to pre- containers at a physiologic temperature (37 6 2°C) for the
vent screw breakage during insertion. The torsional strength specified testing periods shall be used. It shall be well stirred
shall be determined using the test methods described in Annex during the test and shall be provided with a means of raising
A1. the temperature at a uniform rate.
6.1.3 Driving Torque is an important parameter to avoid 7.1.4 pH Meter—A pH metering device sensitive in the
failure of the screw during insertion and to ensure that the physiological range (pH 6 to pH 8) with a precision of 0.02 or
screw may be easily inserted by the surgeon. The insertion better shall be used.
torque should be much less than the torsional yield strength of 7.1.5 Balance—A calibrated weighing device capable of
thescrewaswellasthatoftheappropriatescrewdriverbit.The measuring the weight of a sample to a precision of 0.1 % of its
insertion torque may be determined using the test methods initial weight shall be used.
described in Annex A2. 7.1.6 Driving Instruments—Specification F116 provides re-
6.1.4 Axial Pullout Strength is an important parameter if the lated dimensional information for several types of medical
screwissubjectedtoaxialtensileforces,orifthescrewisfixed screwdrivers
into poor quality or osteoporotic bone. The pullout strength
7.2 Sample Acquisition and Evaluation Frequency:
may be determined using the test methods described in Annex
7.2.1 Sampling—If appropriate, representative random
A3.
samples shall be taken from each lot or processing quantity in
6.2 Absorbable Bone Plates: accordance with Practice E122. The test specimen shall be a
6.2.1 Geometric Considerations—Bone plates that are in- completely fabricated and finished absorbable bone screw
tended to be used with bone screws shall have design features sterilized as intended by the manufacturer.
(screw holes or slots) that conform to or appropriately fit the 7.2.2 Conditioning Intervals—For a complete history of the
corresponding bone screw. behaviorofasampleduringabsorption,thereshouldbeatleast
6.2.2 Bending Properties—The bending properties are criti- seven measuring points spanning the duration of mechanical
cal characteristics of bone plates for orthopedic applications longevity. For example, 0 h, 1 day, 1 week, 4 weeks, 8 weeks,
since the bone plate provides the primary means of stabilizing 12 weeks, 16 weeks, and 24 weeks may be appropriate for
the bone fragments. In addition, the bending stiffness of the L-PLA based devices. An initial (0 h) sample is to be tested
bone plate may affect the rate and quality of healing. without conditioning, while data acquired at 1 day post-
6.2.2.1 The relevant bending properties (bending stiffness, immersion provides representation of an initial equilibration of
bending structural stiffness, and bending strength) shall be the sample within the conditioning solution. The testing
determined using the standard test method of Annex A4. intervals shall be documented in the test report.
7.3 Sample Conditioning:
7. General Sampling, Conditioning, and Testing
7.3.1 Test specimens shall be conditioned by immersion in
Considerations
a pH-controlled aqueous solution at physiologic temperatures
(37 6 2°C) for time intervals appropriate for the device(s)
7.1 Apparatus, Equipment, and Materials:
7.1.1 Sample Container—A self-enclosed glass or plastic being evaluated.
container capable of holding the test sample and the condition- 7.3.1.1 Conditioning without Loading—This approach,
ing solution shall be used. The container shall be sealable to which omits mechanical loading, is the most common and
exposes the sample only to hydrolysis. Such conditioning
preventsolutionlossduetoevaporation.Multiplesamplesmay
be stored in the same container provided that suitable sample necessitates a subsequent test to quantify the impact of
hydrolysis on the sample’s mechanical properties.
separation is maintained to allow fluid access to each sample
surface and to preclude sample-to-sample contact. 7.3.1.2 Conditioning under Applied Load—If the device is
7.1.2 Conditioning/Soaking Solution—Aphosphatebuffered intended for use in a loaded physiological condition, it is
saline (PBS) or other adequately pH-controlled aqueous solu- important to consider characterization of the influence that
tion shall be used. The pH of the solution shall be maintained static and/or fatigue loading have on the deterioration of the
at 7.4 6 0.2 (see Test Method F1635, Section X1.3). The pH testspecimen.Conditioningloadtypesandmagnitudesthatare
representative of anticipated physiological conditions should
should be monitored frequently and, if necessary, the solution
shall be changed periodically in order to maintain the pH be used.
within the acceptable limits.These materials may be hazardous 7.3.2 Conclusion of Conditioning—Once the appropriate
and all persons using them should review the material safety thermal conditioning period is complete, the immersed sample
data sheet (MSDS) before handling and use all recommended is then removed from the elevated temperature bath. The
safety precautions. thermally conditioned sample is to remain immersed in the
F2502−17
conditioning fluid until mechanical testing is commenced. 7.4.4 Room Temperature Testing—Testing is to be per-
Testingshallcommencewithin1hofsampleretrievalfromthe formed at room temperature (23 6 2°C). Unless otherwise
elevated temperature bath. deemed relevant, samples should be tested in a non-dried or
wet condition per Practice F1635. Testing of dried or drying
7.4 Sample Testing:
samples shall be avoided due to potential to affect the values
7.4.1 Care and Handling—Care, handling, and positioning
and/or variability of the mechanical property under measure-
of the absorbable device sample should be conducted in
ment.
accordance with Practice F565, as appropriate.
7.4.5 Immersion Testing (Optional)—The best approxima-
7.4.1.1 Consider Practice F2503 to identify potential haz-
tion of in vivo loading is to test specimens while fully
ards produced by interactions between the device and the MR
immersed in water at 37°C. Depending on the sample and test
environment and for terms that may be used to label the device
method, such testing can often be impractical to implement,
for safety in the MR environment.
which leads to the herein optional designation. However, if
7.4.2 Timing—Testing shall commence within 1 h after the
conducted, such immersion testing can replace room tempera-
sample container is retrieved from the elevated temperature
ture testing.
bath.
7.4.6 Reporting Requirements—The selected sample testing
7.4.3 Retrieval—Testing is to occur immediately after re-
condition shall be included in the report (See X1.4).
moval of the thermally conditioned sample from the condition-
8. Keywords
ing solution. Once retrieved, excess fluid shall be removed and
the sample shall be then promptly positioned in accordance 8.1 absorbable; bend testing; bone plates; bone screw;
with the specific test method. conditioning; dimensions; insertion; pullout; shear; torsion
ANNEXES
(Mandatory Information)
A1. TEST METHOD FOR DETERMINING THE TORSIONAL PROPERTIES OF ABSORBABLE BONE SCREWS
A1.1 Scope have sufficient sensitivity so as to enable an accurate offset
measurement capability for a 2° angular displacement (see
A1.1.1 This test method describes methods for torsion
A1.4.6).
testing in order to determine intrinsic and structural properties
of absorbable bone screws. It measures the torsional yield
A1.2.2 Pilot holes in test block—Pilot holes shall be drilled
strength, maximum torque, and breaking angle of the bone
in the test block for insertion and removal of the test specimen.
screw under standard conditions.
See Specification F543, Annex 2.
A1.1.2 This test method is intended to provide a means of
A1.2.3 Test block—The test block shall be fabricated from a
mechanically characterizing different bone screw designs. It is
uniform material that conforms to Specification F1839. See
not the intention of this test method to define levels of
Specification F543, Annex 2.
performance for bone screws as insufficient knowledge is
available to predict the consequences of the use of particular A1.2.4 Testing fixture—The torsion testing apparatus that is
bone screw designs. to be used for applying the required torque to the specimen
shall be calibrated for the range of torques and rotational
A1.1.3 Factors considered important, but for which values
displacements used in the determination. A suitable testing
and test methods have not been established, are the shear
fixture for the torsional yield strength-maximum torque-
strength of the head of a screw, shear strength of the threaded
breaking angle test is illustrated in Fig. A1.1.
region of a screw, and clinically relevant in vitro conditioning
of enzymatically degradable polymer resins.
A1.2.5 Test specimen—The test specimen shall be a com-
pletelyfabricatedandfinishedabsorbablebonescrewsterilized
A1.1.4 Units—The values stated in SI units are to be
as intended by the manufacturer.
regarded as standard. No other units of measurement are
included in this standard.
A1.2.6 Torque transducer—A transducer to translate the
applied torque into an electrical signal capable of continuous
A1.2 Apparatus
recording, calibrated over the range of torques, both in clock-
A1.2.1 Data acquisition device—The data recorder shall be
wise and counterclockwise rotation, to be encountered in the
suitable for continuously recording torque versus angle of
test method, shall be provided.
rotation, and linear displacement, calibrated in units of
Newton-meters for torque and degrees for angle of rotation. A1.2.7 Torsional displacement transducer—Atransducer to
translate the angle of twist into an electrical signal capable of
The value of torque shall have a resolution of at least 5 % of
torsional yield strength. The angular displacement scale shall continuous recording, calibrated over the range of angles to be
F2502−17
A1.4.4 The torsional yield strength shall be determined by
the offset method (see Fig.A1.2), using the torque versus angle
of rotation curve.
A1.4.5 On the torque versus angle of rotation curve, locate
point m equal to a rotation of 2°. Draw line mn parallel to OA,
and locate b, the intersection of line mn with the torque versus
angle of rotation curve. Torque B is defined as the torsional
yield strength.
A1.4.6 The maximum torque is determined by the largest
value of torque on the torque versus angle of rotation curve.
A1.4.7 Absorbable bone screws typically do not exhibit a
distinctive failure point due to the plastic tearing that occurs
once the maximum torque has been reached. Therefore, the
breaking angle shall be defined as the angle of rotation at the
FIG. A1.1Example of a Test Setup
point where the maximum torque is reported.
A1.5 Report
A1.5.1 Report the following information for each specimen
encountered in the test and with an accuracy of 61% of
tested:
reading, both in clockwise and counterclockwise rotation, shall
A1.5.1.1 Screw identification. Reference any applicable
be used.
ASTM or ISO specification that may apply to the specimen.
A1.5.1.2 Screw composition.
A1.3 Testing
A1.5.1.3 Gauge length.
A1.3.1 The test samples shall be completely immersed in
A1.5.1.4 Test speed.
the solution.
A1.5.1.5 Number of specimens tested.
A1.3.2 The test blocks shall be pre-soaked in the same A1.5.1.6 Conditioning details.
solution as the samples. The blocks can be pre-drilled but A1.5.1.7 Solution.
should be tapped after removal from the solution. A1.5.1.8 Loaded or unloaded (if loaded, list the load).
A1.5.1.9 Torsional yield strength.
A1.4 Procedure
A1.5.1.10 Maximum torque.
A1.5.1.11 Mean and standard deviations of the yield
A1.4.1 Place the specimen in the holding device so that five
threads below the head of the screw are exposed outside the strength for the set of screws tested.
A1.5.1.12 Mean and standard deviations of the maximum
holdingdevice(forexample,asplitcollet).Ifthetestspecimen
torque for the set of screws tested.
cannot accommodate this setup because the screw is too small
A1.5.1.13 Torque versus angle of rotation plot.
or is partially threaded, alternate procedures may be used but
A1.5.1.14 Grip length.This does not have to be reported for
shall be described in the test report. For fully threaded screws
a fully threaded screw of ASTM or ISO specification whose
that are too small, the gauge length of the specimen should
overall length is given.
represent20 %ofthethreadedportionofthetestspecimen.For
A1.5.1.15 Fracture location. The location can be specified
partially threaded screws, a large enough portion of the screw
by listing the number of threads below the head at which the
thread should be gripped to firmly secure the screw so that it
does not rotate when under the torsional load. There are no
specific requirements for the gauge length or the grip length in
this case; however, at least one full thread shall be exposed, if
possible. Since the gauge length and grip length can vary for
these screws, the only requirement is that both be reported.
A1.4.2 The gauge length or grip length should be kept the
same length for a test of similar design. If a split collet and
colletholderareused,thefollowingtestmethodisappropriate:
Place the split collet in the collet holder. Clamp the split collet
andholderinthevise.Theclampingforceoftheviseshouldbe
sufficient to prevent rotation of the screw or the split collet.
Drive the specimen in the direction of insertion, using an
appropriate size and configured screwdriver bit, by applying a
torsional force. If an axial load is required to maintain the
screwdriver bit in the screw head, its value should be noted.
A1.4.3 Test Speed—The torsional force shall be applied at a
constant rate between 1 to 5 revolutions/min. FIG. A1.2Typical Torque versus Angle of Rotation Curve
F2502−17
screw fails or by measuring the distance below the head to the A1.6.2 Bias—No statement of bias can be made, since no
approximate fracture point. acceptable reference values are available, nor can they be
A1.5.1.16 Additional damage. Indicate if any damage to the
obtained since this test is a destructive test.
test specimen occurred during the test (for example, stripping
of the head, deformation of the test specimen, and so forth).
A1.6 Precision and Bias
A1.6.1 Precision—Dataestablishingtheprecisionofthetest
method have not yet been obtained.
A2. TEST METHOD FOR DRIVING TORQUE OF ABSORBABLE BONE SCREWS
A2.1 Scope A2.3.1.3 Comparative Screw Performance Tests—Insert
eachscrewintoatestblock,whosethicknessisgreaterthanthe
A2.1.1 This test method is used to measure the torque
length of the screw being tested, until the greatest equivalent
required to drive a bone screw into a standard material. The
insertion depth possible for all of the screw designs being
results obtained in this test method bear no direct correlation to
compared is reached.
the insertion torque required to insert the subject bone screw in
human or animal bo
...

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: F2502 − 11 F2502 − 17
Standard Specification and Test Methods for
Absorbable Plates and Screws for Internal Fixation
Implants
This standard is issued under the fixed designation F2502; 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 specification and test methods cover the mechanical characterization of plates and screws for orthopedic internal
fixation. Covered devices are fabricated from one or more hydrolytically degradable polymer (from this point on referred to as
“absorbable”) resins or resin composites.
1.2 This specification establishes a common terminology to describe the size and other physical characteristics of absorbable
implants and performance definitions related to the performance of absorbable devices.
1.3 This specification establishes standard test methods to consistently measure performance-related mechanical characteristics
of absorbable devices when tested under defined conditions of pretreatment, temperature, humidity, and testing machine speed.
1.4 This specification may not be appropriate for all absorbable devices, especially those that possess limited hydrolytic
susceptibility and degrade in vivo primarily through enzymatic action. The user is cautioned to consider the appropriateness of the
standard in view of the particular absorbable device and its potential application.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 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.
1.7 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:
D790 Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or
Process
E1823 Terminology Relating to Fatigue and Fracture Testing
F116 Specification for Medical Screwdriver Bits
F382 Specification and Test Method for Metallic Bone Plates
F543 Specification and Test Methods for Metallic Medical Bone Screws
F565 Practice for Care and Handling of Orthopedic Implants and Instruments
F1088 Specification for Beta-Tricalcium Phosphate for Surgical Implantation
F1185 Specification for Composition of Hydroxylapatite for Surgical Implants
F1635 Test Method for in vitro Degradation Testing of Hydrolytically Degradable Polymer Resins and Fabricated Forms for
Surgical Implants
This specification and test methods is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility
of Subcommittee F04.21 on Osteosynthesis.
Current edition approved June 1, 2011Sept. 1, 2017. Published July 2011October 2017. Originally approved in 2005. Last previous edition approved in 20092011 as
ε1
F2502 – 05 (2009)F2502 – 11. . DOI: 10.1520/F2502-11.10.1520/F2502-17.
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
F2502 − 17
F1839 Specification for Rigid Polyurethane Foam for Use as a Standard Material for Testing Orthopaedic Devices and
Instruments
F1925 Specification for Semi-Crystalline Poly(lactide) Polymer and Copolymer Resins for Surgical Implants
F2313 Specification for Poly(glycolide) and Poly(glycolide-co-lactide) Resins for Surgical Implants with Mole Fractions Greater
Than or Equal to 70 % Glycolide
F2503 Practice for Marking Medical Devices and Other Items for Safety in the Magnetic Resonance Environment
F2579 Specification for Amorphous Poly(lactide) and Poly(lactide-co-glycolide) Resins for Surgical Implants
F2902 Guide for Assessment of Absorbable Polymeric Implants
F3160 Guide for Metallurgical Characterization of Absorbable Metallic Materials for Medical Implants
2.2 ISO Standards:
ISO 13781 Poly (L-Lactide) Resins and Fabricated Forms for Surgical Implants—In Vitro Degradation Testing
ISO 14630 Non-Active Surgical Implants—General Requirements
ISO 15814 Copolymers and Blends Based on Polylactide—In Vitro Degradation Testing
3. Terminology
3.1 Definitions:
3.1.1 Unless otherwise defined in this specification, the terminology related to mechanical testing that is used in these test
methods will be in accordance with the definitions of Terminologies E6 and E1823, and Specifications F382 and F543.
3.2 General Definitions:
3.2.1 absorbable, adj—in the body, referring to an initially distinct foreign material or substance that either directly or through
intended degradation can pass through or be assimilated by cells and/or tissue.
NOTE 1—See Appendix X1.5 for a discussion regarding the usage of “absorbable” and other related terms.
3.2.2 absorbable composite—an absorbable polymer resin or construct incorporating a particulate and/or fibrous bioactive
and/or absorbable filler material.
3.2.3 bone anchor—a device or a component of a device that provides the attachment to the bone.
3.2.4 bone plate—a device, when affixed with screws or cerclage wire, intended to provide alignment of two or more bone
sections, primarily by spanning the fracture or defect. A bone plate has two or more holes. Its width and thickness usually are not
the same in magnitude.
3.2.5 deterioration—the reduction or worsening of mechanical or other functional performance properties of a device.
3.2.6 hydrolytically degradable polymer—any polymeric material in which the primary mechanism of chemical degradation in
the body is by hydrolysis (water reacting with the polymer resulting in cleavage of the chain).
3.2.7 suture anchor—a device that provides a means to attach soft tissue to bone with a suture.
3.3 Definitions of Terms Specific to This Standard:
3.3.1 insertion depth (mm)—the linear advancement of a device into the test block measured relative to its seated position at
the test block’s surface prior to testing.
4. Significance and Use
4.1 Absorbable devices are intended to degrade and absorb over time once they are implanted into the body. This makes a
removal operation unnecessary, which is especially advantageous for pediatric patients.
4.2 While the polymer degrades due to hydrolytic reaction with the environment, the mechanical performance of the device also
deteriorates. The key to developing mechanically effective fracture fixation systems based on absorbable devices is to provide an
adequate level of fixation strength and stiffness for a time frame that exceeds that expected for fracture healing. Once the fracture
is healed, the device can be completely absorbed by the body. The biological performance of the device, particularly for application
at a bony site, may be enhanced by incorporation of bioactive fillers in the polymer.
4.3 Absorbable devices will be tested using test methods that are similar to those used to evaluate conventional metallic devices.
The pre-test conditioning requirements, handling requirements, and time-dependent mechanical property evaluations for
absorbable devices shall be considered.
4.4 This specification and accompanying test methods are intended to complement the more general considerations for the
assessment of absorbable polymeric implants that are described within Guide F2902.
5. Materials and Manufacture
5.1 Absorbable devices may be fabricated from one of the following materials:
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
F2502 − 17
FIG. 1 Screw Parameters
5.1.1 L-lactide, D-lactide, D, L-lactide, glycolide, or other known hydrolytically degradable polymer resins or copolymers. (See
ISO 13781, ISO 15814, Test Method (for additional information, see complementary test methods found in ISO 13781, ISO 15814,
and F1635, and in related Specifications F1925, F1088F2313, and F1185F2579.)
5.1.2 Other absorbable polymeric, ceramic, or metallic based constructs that degrade through non-hydrolytic means, such as
those described in Specifications F1088 and F1185, and Guide F3160 may be considered, but precautions should be undertaken
to assure a materials-appropriate degradation environment is maintained.
5.2 The manufacturer shall ensure that materials used to manufacture absorbable implants are suitable for implanting into the
body. Methods to evaluate a material’s suitability are described in ISO 14630.
5.3 All absorbable devices made of materials that have an ASTM committee F04 or D20 standard designation or an ISO
designation shall meet those requirements given in the ASTM standards.
6. General Requirements and Performance Considerations
6.1 Absorbable Bone Screws—The following properties may be important when determining the suitability of a screw for a
particular application. However, the test methods referenced as follows may not be appropriate for all types of implant applications.
The user is cautioned to consider the appropriateness of the test methods in view of the devices being tested and their potential
application.
6.1.1 Offset Yield Strength is the stress at which the stress-strain curve departs from linearity by a specified percent of
deformation (offset).
6.1.2 Torsional Strength is an important parameter to prevent screw breakage during insertion. The torsional strength shall be
determined using the test methods described in Annex A1.
6.1.3 Driving Torque is an important parameter to avoid failure of the screw during insertion and to ensure that the screw may
be easily inserted by the surgeon. The insertion torque should be much less than the torsional yield strength of the screw as well
as that of the appropriate screwdriver bit. The insertion torque may be determined using the test methods described in Annex A2.
6.1.4 Axial Pullout Strength is an important parameter if the screw is subjected to axial tensile forces, or if the screw is fixed
into poor quality or osteoporotic bone. The pullout strength may be determined using the test methods described in Annex A3.
6.2 Absorbable Bone Plates:
6.2.1 Geometric Considerations—Bone plates that are intended to be used with bone screws shall have design features (screw
holes or slots) that conform to or appropriately fit the corresponding bone screw.
6.2.2 Bending Properties—The bending properties are critical characteristics of bone plates for orthopedic applications since the
bone plate provides the primary means of stabilizing the bone fragments. In addition, the bending stiffness of the bone plate may
affect the rate and quality of healing.
6.2.2.1 The relevant bending properties (bending stiffness, bending structural stiffness, and bending strength) shall be
determined using the standard test method of Annex A4.
7. General Sampling, Conditioning, and Testing Considerations
7.1 Apparatus, Equipment, and Materials:
7.1.1 Sample Container—A self-enclosed glass or plastic container capable of holding the test sample and the conditioning
solution shall be used. The container shall be sealable to prevent solution loss due to evaporation. Multiple samples may be stored
in the same container provided that suitable sample separation is maintained to allow fluid access to each sample surface and to
preclude sample-to-sample contact.
7.1.2 Conditioning/Soaking Solution—A phosphate buffered saline (PBS) or other adequately pH-controlled aqueous solution
shall be used. The pH of the solution shall be maintained at 7.4 6 0.2 (see Test Method F1635, Section X1.3). The pH should be
monitored frequently and, if necessary, the solution shall be changed periodically in order to maintain the pH within the acceptable
limits. These materials may be hazardous and all persons using them should review the material safety data sheet (MSDS) before
handling and use all recommended safety precautions.
F2502 − 17
7.1.2.1 Other physiologic relevant solutions may be substituted provided the solution is properly buffered. An anti-microbial
additive should be used to inhibit the growth of microorganisms in the solution during the test period. The investigator shall
demonstrate that the chosen antimicrobial does not affect the absorption rate (see X1.3).
7.1.3 Constant Temperature Bath or Oven—An aqueous bath or heated air oven capable of maintaining the samples and
containers at a physiologic temperature (37 6 2°C) for the specified testing periods shall be used. It shall be well stirred during
the test and shall be provided with a means of raising the temperature at a uniform rate.
7.1.4 pH Meter—A pH metering device sensitive in the physiological range (pH 6 to pH 8) with a precision of 0.02 or better
shall be used.
7.1.5 Balance—A calibrated weighing device capable of measuring the weight of a sample to a precision of 0.1 % of its initial
weight shall be used.
7.1.6 Driving Instruments—Specification F116 provides related dimensional information for several types of medical
screwdrivers
7.2 Sample Acquisition and Evaluation Frequency:
7.2.1 Sampling—If appropriate, representative random samples shall be taken from each lot or processing quantity in
accordance with Practice E122. The test specimen shall be a completely fabricated and finished absorbable bone screw sterilized
as intended by the manufacturer.
7.2.2 Conditioning Intervals—For a complete history of the behavior of a sample during absorption, there should be at least
seven measuring points spanning the duration of mechanical longevity. For example, 0 h, 1 day, 1 week, 4 weeks, 8 weeks, 12
weeks, 16 weeks, and 24 weeks may be appropriate for L-PLA based devices. An initial (0 h) sample is to be tested without
conditioning, while data acquired at 1 day post-immersion provides representation of an initial equilibration of the sample within
the conditioning solution. The testing intervals shall be documented in the test report.
7.3 Sample Conditioning:
7.3.1 Test specimens shall be conditioned by immersion in a pH-controlled aqueous solution at physiologic temperatures (37
6 2°C) for time intervals appropriate for the device(s) being evaluated.
7.3.1.1 Conditioning without Loading—This approach, which omits mechanical loading, is the most common and exposes the
sample only to hydrolysis. Such conditioning necessitates a subsequent test to quantify the impact of hydrolysis on the sample’s
mechanical properties.
7.3.1.2 Conditioning under Applied Load—If the device is intended for use in a loaded physiological condition, it is important
to consider characterization of the influence that static and/or fatigue loading have on the deterioration of the test specimen.
Conditioning load types and magnitudes that are representative of anticipated physiological conditions should be used.
7.3.2 Conclusion of Conditioning—Once the appropriate thermal conditioning period is complete, the immersed sample is then
removed from the elevated temperature bath. The thermally conditioned sample is to remain immersed in the conditioning fluid
until mechanical testing is commenced. Testing shall commence within 1 h of sample retrieval from the elevated temperature bath.
7.4 Sample Testing:
7.4.1 Care and Handling—Care, handling, and positioning of the absorbable device sample should be conducted in accordance
with Practice F565, as appropriate.
7.4.1.1 Consider Practice F2503 to identify potential hazards produced by interactions between the device and the MR
environment and for terms that may be used to label the device for safety in the MR environment.
7.4.2 Timing—Testing shall commence within 1 h after the sample container is retrieved from the elevated temperature bath.
7.4.3 Retrieval—Testing is to occur immediately after removal of the thermally conditioned sample from the conditioning
solution. Once retrieved, excess fluid shall be removed and the sample shall be then promptly positioned in accordance with the
specific test method.
7.4.4 Room Temperature Testing—Testing is to be performed at room temperature (23 6 2°C). Unless otherwise deemed
relevant, samples should be tested in a non-dried or wet condition per Practice F1635. Testing of dried or drying samples shall be
avoided due to potential to affect the values and/or variability of the mechanical property under measurement.
7.4.5 Immersion Testing (Optional)—The best approximation of in vivo loading is to test specimens while fully immersed in
water at 37°C. Depending on the sample and test method, such testing can often be impractical to implement, which leads to the
herein optional designation. However, if conducted, such immersion testing can replace room temperature testing.
7.4.6 Reporting Requirements—The selected sample testing condition shall be included in the report (See X1.4).
8. Keywords
8.1 absorbable; bend testing; bone plates; bone screw; conditioning; dimensions; insertion; pullout; shear; torsion
F2502 − 17
ANNEXES
(Mandatory Information)
A1. TEST METHOD FOR DETERMINING THE TORSIONAL PROPERTIES OF ABSORBABLE BONE SCREWS
A1.1 Scope
A1.1.1 This test method describes methods for torsion testing in order to determine intrinsic and structural properties of absorbable
bone screws. It measures the torsional yield strength, maximum torque, and breaking angle of the bone screw under standard
conditions.
A1.1.2 This test method is intended to provide a means of mechanically characterizing different bone screw designs. It is not the
intention of this test method to define levels of performance for bone screws as insufficient knowledge is available to predict the
consequences of the use of particular bone screw designs.
A1.1.3 Factors considered important, but for which values and test methods have not been established, are the shear strength of
the head of a screw, shear strength of the threaded region of a screw, and clinically relevant in vitro conditioning of enzymatically
degradable polymer resins.
A1.1.4 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
A1.2 Apparatus
A1.2.1 Data acquisition device—The data recorder shall be suitable for continuously recording torque versus angle of rotation,
and linear displacement, calibrated in units of Newton-meters for torque and degrees for angle of rotation. The value of torque shall
have a resolution of at least 5 % of torsional yield strength. The angular displacement scale shall have sufficient sensitivity so as
to enable an accurate offset measurement capability for a 2° angular displacement (see A1.4.6).
A1.2.2 Pilot holes in test block—Pilot holes shall be drilled in the test block for insertion and removal of the test specimen. See
Specification F543, Annex 2.
A1.2.3 Test block—The test block shall be fabricated from a uniform material that conforms to Specification F1839. See
Specification F543, Annex 2.
A1.2.4 Testing fixture—The torsion testing apparatus that is to be used for applying the required torque to the specimen shall be
calibrated for the range of torques and rotational displacements used in the determination. A suitable testing fixture for the torsional
yield strength-maximum torque-breaking angle test is illustrated in Fig. A1.1.
A1.2.5 Test specimen—The test specimen shall be a completely fabricated and finished absorbable bone screw sterilized as
intended by the manufacturer.
A1.2.6 Torque transducer—A transducer to translate the applied torque into an electrical signal amenable tocapable of continuous
recording, calibrated over the range of torques, both in clockwise and counterclockwise rotation, to be encountered in the test
method, shall be provided.
A1.2.7 Torsional displacement transducer—A transducer to translate the angle of twist into an electrical signal amenable tocapable
of continuous recording, calibrated over the range of angles to be encountered in the test and with an accuracy of 61 % of reading,
both in clockwise and counterclockwise rotation, shall be used.
F2502 − 17
FIG. A1.1 Example of a Test Setup
A1.3 Testing
A1.3.1 The test samples shall be completely immersed in the solution.
A1.3.2 The test blocks shall be pre-soaked in the same solution as the samples. The blocks can be pre-drilled but should be tapped
after removal from the solution.
A1.4 Procedure
A1.4.1 Place the specimen in the holding device so that five threads below the head of the screw are exposed outside the holding
device (for example, a split collet). If the test specimen cannot accommodate this setup because the screw is too small or is partially
threaded, alternate procedures may be used but shall be described in the test report. For fully threaded screws that are too small,
the gauge length of the specimen should represent 20 % of the threaded portion of the test specimen. For partially threaded screws,
a large enough portion of the screw thread should be gripped to firmly secure the screw so that it does not rotate when under the
torsional load. There are no specific requirements for the gauge length or the grip length in this case; however, at least one full
thread shall be exposed, if possible. Since the gauge length and grip length can vary for these screws, the only requirement is that
both be reported.
A1.4.2 The gauge length or grip length should be kept the same length for a test of similar design. If a split collet and collet holder
are used, the following test method is appropriate: Place the split collet in the collet holder. Clamp the split collet and holder in
the vise. The clamping force of the vise should be sufficient to prevent rotation of the screw or the split collet. Drive the specimen
in the direction of insertion, using an appropriate size and configured screwdriver bit, by applying a torsional force. If an axial load
is required to maintain the screwdriver bit in the screw head, its value should be noted.
A1.4.3 Test Speed—The torsional force shall be applied at a constant rate between 1 to 5 revolutions/min.
A1.4.4 The torsional yield strength shall be determined by the offset method (see Fig. A1.2), using the torque versus angle of
rotation curve.
A1.4.5 On the torque versus angle of rotation curve, locate point m equal to a rotation of 2°. Draw line mn parallel to OA, and
locate b, the intersection of line mn with the torque versus angle of rotation curve. Torque B is defined as the torsional yield
strength.
A1.4.6 The maximum torque is determined by the largest value of torque on the torque versus angle of rotation curve.
A1.4.7 Absorbable bone screws typically do not exhibit a distinctive failure point due to the plastic tearing that occurs once the
maximum torque has been reached. Therefore, the breaking angle shall be defined as the angle of rotation at the point where the
maximum torque is reported.
F2502 − 17
FIG. A1.2 Typical Torque versus Angle of Rotation Curve
A1.5 Report
A1.5.1 Report the following information for each specimen tested:
A1.5.1.1 Screw identification. Reference any applicable ASTM or ISO specification that may apply to the specimen.
A1.5.1.2 Screw composition.
A1.5.1.3 Gauge length.
A1.5.1.4 Test speed.
A1.5.1.5 Number of specimens tested.
A1.5.1.6 Conditioning details.
A1.5.1.7 Solution.
A1.5.1.8 Loaded or unloaded (if loaded, list the load).
A1.5.1.9 Torsional yield strength.
A1.5.1.10 Maximum torque.
A1.5.1.11 Mean and standard deviations of the yield strength for the set of screws tested.
A1.5.1.12 Mean and standard deviations of the maximum torque for the set of screws tested.
A1.5.1.13 Torque versus angle of rotation plot.
A1.5.1.14 Grip length. This does not have to be reported for a fully threaded screw of ASTM or ISO specification whose overall
length is given.
A1.5.1.15 Fracture location. The location can be specified by listing the number of threads below the head at which the screw fails
or by measuring the distance below the head to the approximate fracture point.
A1.5.1.16 Additional damage. Indicate if any damage to the test specimen occurred during the test (for example, stripping of the
head, deformation of the test specimen, and so forth).
F2502 − 17
A1.6 Precision and Bias
A1.6.1 Precision—Data establishing the precision of the test method have not yet been obtained.
A1.6.2 Bias—No statement of bias can be made, since no acceptable reference values are available, nor can they be obtained since
this test is a destructive test.
A2. TEST METHOD FOR DRIVING TORQUE OF ABSORBABLE BONE SCREWS
A2.1 Scope
A2.1.1 This test method is used to measure the torque required to drive a bone screw into a standard material. The results obtained
in this test method bear no direct correlation to the insertion torque required to insert the subject bone screw in human or animal
bone. This test method is used only for purposes of maintaining the uniformity of the product tested.
A2.2 Testing
A2.2.1 Test Speed—The torsional force shall be applied at a constant rate between 1 to 5 r/min.
A2.3 Procedure
A2.3.1 Insertion—Insert the screw as follows:
A2.3
...