ASTM F2502-05(2009)e1
(Specification)Standard Specification and Test Methods for Bioabsorbable Plates and Screws for Internal Fixation Implants
Standard Specification and Test Methods for Bioabsorbable Plates and Screws for Internal Fixation Implants
SIGNIFICANCE AND USE
Biodegradable devices are expected by intention to deteriorate over time once they are implanted into the body. This makes a removal operation unnecessary, which is especially advantageous especially for pediatric patients.
While the polymer degrades due to hydrolytic reaction with the environment, the mechanical performance of the device also deteriorates. The key to developing effective fracture fixation systems based on biodegradable devices is to provide an adequate level of fixation strength for a time frame that exceeds that expected for fracture healing. Once the fracture is healed, the device can be completely resorbed by the body.
Generally, biodegradable devices will be tested with test methods that are similar to those used to evaluate conventional metallic devices. In addition, one has to take into consideration the pre-test conditioning requirements, handling requirements, and time-dependent mechanical property evaluations for biodegradable devices.
SCOPE
1.1 This specification and test methods covers a mechanical characterization reference for hydrolytically degradable polymer resin (from this point on referenced as “bioabsorbable”) plates and screws for orthopedic internal fixation.
1.2 This specification establishes a common terminology to describe the size and other physical characteristics of bioabsorbable implants and performance definitions related to the performance of bioabsorbable devices.
1.3 This specification establishes standard test methods to consistently measure performance-related mechanical characteristics of bioabsorbable devices when tested under defined conditions of pretreatment, temperature, humidity, and testing machine speed.
1.4 This specification may not be appropriate for all bioabsorbable devices. The user is cautioned to consider the appropriateness of the standard in view of the particular bioabsorbable 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: F2502 – 05 (Reapproved 2009)
Standard Specification and Test Methods for
Bioabsorbable 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.
´ NOTE—Editorial changes were made throughout in December 2009.
1. Scope E4 Practices for Force Verification of Testing Machines
E6 TerminologyRelatingtoMethodsofMechanicalTesting
1.1 This specification and test methods covers a mechanical
E122 Practice for Calculating Sample Size to Estimate,
characterization reference for hydrolytically degradable poly-
With Specified Precision, the Average for a Characteristic
mer resin (from this point on referenced as “bioabsorbable”)
of a Lot or Process
plates and screws for orthopedic internal fixation.
E1823 Terminology Relating to Fatigue and Fracture Test-
1.2 This specification establishes a common terminology to
ing
describe the size and other physical characteristics of bioab-
F116 Specification for Medical Screwdriver Bits
sorbable implants and performance definitions related to the
F382 Specification and Test Method for Metallic Bone
performance of bioabsorbable devices.
Plates
1.3 This specification establishes standard test methods to
F543 Specification and Test Methods for Metallic Medical
consistently measure performance-related mechanical charac-
Bone Screws
teristics of bioabsorbable devices when tested under defined
F565 Practice for Care and Handling of Orthopedic Im-
conditions of pretreatment, temperature, humidity, and testing
plants and Instruments
machine speed.
F1635 Test Method for in vitro Degradation Testing of
1.4 This specification may not be appropriate for all bioab-
Hydrolytically Degradable Polymer Resins and Fabricated
sorbable devices. The user is cautioned to consider the appro-
Forms for Surgical Implants
priateness of the standard in view of the particular bioabsorb-
F1839 Specification for Rigid Polyurethane Foam for Use
able device and its potential application.
as a Standard Material for Testing Orthopaedic Devices
1.5 The values stated in SI units are to be regarded as
and Instruments
standard. No other units of measurement are included in this
F1925 Specification for Semi-Crystalline Poly(lactide)
standard.
Polymer and Copolymer Resins for Surgical Implants
1.6 This standard does not purport to address all of the
2.2 ISO Standards:
safety concerns, if any, associated with its use. It is the
ISO 13781 Poly (L-Lactide) Resins and Fabricated Forms
responsibility of the user of this standard to establish appro-
for Surgical Implants—In Vitro Degradation Testing
priate safety and health practices and determine the applica-
ISO 14630 Non-Active Surgical Implants—General Re-
bility of regulatory limitations prior to use.
quirements
2. Referenced Documents
ISO 15814 Copolymers and Blends Based on
Polylactide—In Vitro Degradation Testing
2.1 ASTM Standards:
D790 Test Methods for Flexural Properties of Unreinforced
3. Terminology
and Reinforced Plastics and Electrical Insulating Materials
3.1 Definitions:
3.1.1 Unless otherwise defined in this specification, the
This specification and test methods is under the jurisdiction of ASTM
terminology related to mechanical testing that is used in these
Committee F04 on Medical and Surgical Materials and Devices and is the direct
test methods will be in accordance with the definitions of
responsibility of Subcommittee F04.21 on Osteosynthesis.
Terminologies E6 and E1823, and Specifications F382 and
Current edition approved Aug. 1, 2009. Published December 2009. Originally
approved in 2005. Last previous edition approved in 2005 as F2502 – 05. DOI:
F543.
10.1520/F2502-05R09.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
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F2502 – 05 (2009)
3.2 General Definitions: 3.5.1 bone plate—a device with two or more holes or slots,
3.2.1 bioabsorbable device—a class of implants that are or both, and a cross section that consists of at least two
dimensions (width and thickness), which generally are not the
designed to deteriorate by means of biological resorption once
they are implanted into the body. same in magnitude. The device is intended to provide align-
ment and fixation of two or more bone sections, primarily by
3.2.2 biological resorption—process by which degraded
spanning the fracture or defect.
biomaterials(thatis,productsofdegradation)areeliminatedor
3.5.2 bone plate length, L (mm)—the linear dimension of
incorporated, or both, by means of physiological metabolic
the bone plate measured along the longitudinal axis as illus-
routes.
trated in Fig. A4.2.
3.2.3 deterioration (of a bioabsorbable device)—the action
3.5.3 bone plate thickness, b (mm)—the linear dimension of
or process that results in a reduction of mass or mechanical
the bone plate measured parallel to the screw hole axis as
performance properties, or both.
shown in Fig. A4.2. For a bone plate with a crescent section,
3.2.4 hydrolytically degradable polymer (HDP)—any poly-
the thickness is measured at the thickest point along the
meric material in which the primary mechanism of chemical
section.
degradation in the body is by hydrolysis (water reacting with
3.5.4 bone plate width, w (mm)—thelineardimensionofthe
the polymer resulting in cleavage of the chain).
bone plate measured perpendicular to both the length and
3.3 Definitions for Apparatus:
thickness axes as shown in Fig. A4.2.
3.3.1 data acquisition device—the data recorder shall be
suitable to continuously record torque versus angle of rotation,
4. Significance and Use
as well as linear displacement, calibrated in units of Newton-
4.1 Biodegradable devices are expected by intention to
metres for torque and degrees for angle of rotation. The value
deteriorate over time once they are implanted into the body.
of torque shall have a resolution of at least 5 % of torsional
This makes a removal operation unnecessary, which is espe-
yield strength. The angular displacement scale shall have a
cially advantageous especially for pediatric patients.
minimum sensitivity so as to enable an accurate offset mea-
4.2 While the polymer degrades due to hydrolytic reaction
surement capability for a 2° angular displacement (seeA1.5.3).
with the environment, the mechanical performance of the
3.3.2 pilot holes in test block—pilot holes shall be drilled in
device also deteriorates. The key to developing effective
the test block for insertion and removal of the test specimen.
fracture fixation systems based on biodegradable devices is to
See Specification F543, Annex 2.
provide an adequate level of fixation strength for a time frame
3.3.3 test block—the test block shall be fabricated from a
that exceeds that expected for fracture healing. Once the
uniform material that conforms to Specification F1839. See
fractureishealed,thedevicecanbecompletelyresorbedbythe
Specification F543, Annex 2.
body.
3.3.4 testing fixture—the torsion testing apparatus that is to
4.3 Generally, biodegradable devices will be tested with test
be used for applying the required torque to the specimen shall
methods that are similar to those used to evaluate conventional
be calibrated for the range of torques and rotational displace-
metallic devices. In addition, one has to take into consideration
ments used in the determination. A suitable testing fixture for
the pre-test conditioning requirements, handling requirements,
the torsional yield strength-maximum torque-breaking angle
and time-dependent mechanical property evaluations for bio-
test is illustrated in Fig. A1.1.
degradable devices.
3.3.5 test specimen—the test specimen shall be a com-
pletely fabricated and finished bioabsorbable bone screw.
5. Materials and Manufacture
3.3.6 torque transducer—a transducer to translate the ap-
5.1 Bioabsorbable devices may be fabricated from one of
plied torque into an electrical signal amenable to continuous
the following materials:
recording, calibrated over the range of torques, both in the
5.1.1 L-lactide, D-lactide, D, L-lactide, glycolide, or other
clockwise and counterclockwise rotation, to be encountered in
known hydrolytically degradable polymer resins or copoly-
the test method, shall be provided.
mers. (See ISO 13781, ISO 15814, Test Method F1635, and
3.3.7 torsional displacement transducer—a transducer to
Specification F1925.)
translate the angle of twist into an electrical signal amenable to
5.2 The manufacturer is responsible to ensure that materials
continuous recording, calibrated over the range of angles to be
used to manufacture bioabsorbable implants are suitable for
encountered in the test and an accuracy of 61 % of reading,
both in the clockwise and counterclockwise rotation, shall be
used.
3.4 Definitions for Screw Testing:
3.4.1 anchor—a bioabsorbable device or a component of a
bioabsorbable device that provides the attachment to the bone.
3.4.2 bone anchor—a bioabsorbable device that provides a
means to attach soft tissue to bone with a suture.
3.4.3 insertion depth (mm)—the linear advancement of the
bioabsorbabledeviceintothetestblockmeasuredrelativetoits
seated position at the test block’s surface prior to testing.
3.5 Definitions for Plate Testing: FIG. 1 Screw Parameters
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F2502 – 05 (2009)
implanting into the body. Methods to evaluate a material’s 8. Performance Requirements
suitability are described in ISO 14630.
8.1 Factors considered being important, but for which
5.3 All bioabsorbable devices made of materials that have
values and test methods have not been established, are shear
an ASTM committee F04 or D20 standard designation or an
strength of the head of a screw, shear strength of the threaded
ISO designation shall meet those requirements given in the
region of a screw, and enzymatically degradable polymer
ASTM standards.
resins.
5.4 Soaking Solution—A phosphate buffered saline (PBS)
solution shall be used. The pH of the solution shall be
9. Driving Instruments
maintained at 7.4 6 0.2 (see Test Method F1635, Section
9.1 Specification F116 provides related dimensional infor-
X1.3). The pH should be monitored frequently and, if need be,
mation for several types of medical screwdrivers.
the solution should be changed periodically in order to main-
tain the pH within the acceptable limits.
10. General Requirements and Performance
5.4.1 Other physiologic solutions may be substituted pro-
Considerations
vided the solution is properly buffered. An anti-microbial
10.1 The following properties may be important when
additive should be used to inhibit the growth of microorgan-
determining the suitability of a screw for a particular applica-
isms in the solution during the test period. The investigator
tion. However, the test methods referenced as follows may not
must demonstrate that the chosen antimicrobial does not affect
be appropriate for all types of implant applications. The user is
the degradation rate (see X1.3).
cautionedtoconsidertheappropriatenessofthetestmethodsin
5.5 Sample Container—A self-enclosed container capable
view of the devices being tested and their potential application.
ofholdingthetestsampleandthesolution(seeX1.4).Multiple
10.1.1 Offset Yield Strength is the stress at which the
samples may be stored in the same container provided that
stress-strain curve departs from linearity by a specified percent
suitable sample separation is maintained to allow fluid access
of deformation (offset).
to each sample surface and to preclude sample-to-sample
10.1.2 Torsional Strength is an important parameter to
contact. Each container shall be sealable against solution loss
preventscrewbreakageduringinsertion.Thetorsionalstrength
due to evaporation.
shall be determined using the test methods described inAnnex
5.6 Constant Temperature Bath or Oven—An aqueous bath
A1.
or heated air oven capable of maintaining the samples and
10.1.3 Axial Pullout Strength is an important parameter if
containers at physiologic temperatures (37 6 2°C) for the
the screw is subjected to axial tensile forces, or if the screw is
specified testing periods.
fixed into poor quality or osteoporotic bone. The pullout
5.7 pH Meter—A pH metering device sensitive in the
strengthmaybedeterminedusingthetestmethodsdescribedin
physiological range (pH 6 to pH 8) with a precision of 0.02 or
Annex A3.
better.
10.1.4 Insertion Torque is an important parameter to avoid
5.8 Balance—Acalibratedweighingdevicecapableofmea-
failure of the screw during insertion and to ensure that the
suring the weight of a sample to a precision of 0.1 % of its
screw may be easily inserted by the surgeon. The insertion
initial weight.
torque should be much less than the torsional yield strength of
thescrewaswellasthatoftheappropriatescrewdriverbit.The
6. Conditioning
insertion torque may be determined using the test methods
6.1 Conditioning—Condition the test specimens in a suit-
described in Annex A2.
ablesolution(forexample,PBSsolution)andtemperatureuntil
10.1.5 Geometric Considerations—Bone plates that are in-
itistimetobetested.Removethemfromthesolutionandwipe
tended to be used with bone screws shall have design features
off excess solution.The specimens shall be tested within1hof
(screw holes or slots) that conform to or appropriately fit the
rinsing (see Test Method F1635). In addition to conditioning
corresponding bone screw.
the test specimen in suitable solutions, if the test specimen is
10.1.6 Bending Properties—The bending properties are
intended for use in a loaded physiological condition, it may be
critical characteristics of bone plates for orthopedic applica-
important to address the additional influence of conditioning
tions since the bone plate provides the primary means of
static or fatigue loads, or both, on the deterioration of the test
stabilizing the bone fragments. Additionally, the bending
specimen. Conditioning loads that are representative of antici-
stiffness of the bone plate may directly affect the rate and
pated physiological conditions should be chosen.
ability of healing.
6.1.1 Test Conditions—Conduct tests at 23 6 2ºC and 50 6
10.1.6.1 The relevant bend
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