ASTM F1541-17

Standard Specification and Test Methods for External Skeletal Fixation Devices

SIGNIFICANCE AND USE
A1.4 Significance and Use
A1.4.1 The purpose of this classification is to establish a consistent terminology system by means of which these ESFD configurations can be classified. It is anticipated that a companion testing standard using this classification system will subsequently be developed.
SCOPE
1.1 This specification provides a characterization of the design and mechanical function of external skeletal fixation devices (ESFDs), test methods for characterization of ESFD mechanical properties, and identifies needs for further development of test methods and performance criteria. The ultimate goal is to develop a specification, which defines performance criteria and methods for measurement of performance-related mechanical characteristics of ESFDs and their fixation to bone. It is not the intention of this specification to define levels of performance or case-specific clinical performance of the devices, as insufficient knowledge is available to predict the consequences of the use of any of these devices in individual patients for specific activities of daily living. Furthermore, it is not the intention of this specification to describe or specify specific designs for ESFDs.  
1.2 This specification describes ESFDs for surgical fixation of the skeletal system. It provides basic ESFD geometrical definitions, dimensions, classification, and terminology; material specifications; performance definitions; test methods; and characteristics determined to be important to the in-vivo performance of the device.  
1.3 This specification includes a terminology and classification annex and five standard test method annexes as follows:  
1.3.1 Classification of External Fixators—Annex A1.  
1.3.2 Test Method for External Skeletal Fixator Connectors—Annex A2.  
1.3.3 Test Method for Determining In-Plane Compressive Properties of Circular Ring or Ring Segment Bridge Elements—Annex A3.  
1.3.4 Test Method for External Skeletal Fixator Joints—Annex A4.  
1.3.5 Test Method for External Skeletal Fixator Pin Anchorage Elements—Annex A5.  
1.3.6 Test Method for External Skeletal Fixator Subassemblies—Annex A6.  
1.3.7 Test Method for External Skeletal Fixator/Constructs Subassemblies—Annex A7.  
1.4 A rationale is given in Appendix X1.  
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 Multiple test methods are included in this standard. However, the user is not necessarily obligated to test using all of the described methods. Instead, the user should only select, with justification, test methods that are appropriate for a particular device design. This may be only a subset of the herein described test methods  
1.7 The following safety hazards caveat pertains only to the test method portions (Annex A2 – Annex A6):  
1.8 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.  
1.9 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 F1541-02(2015) - Standard Specification and Test Methods for External Skeletal Fixation Devices
• 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 F366-24 - Standard Specification for Fixation Pins and Wires
• Effective Date: 01-Jan-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 A938-18 - Standard Test Method for Torsion Testing of Wire
• Effective Date: 01-Sep-2018
• Refers: ASTM E1942-98(2018)e1 - Standard Guide for Evaluating Data Acquisition Systems Used in Cyclic Fatigue and Fracture Mechanics Testing
• Effective Date: 01-Jun-2018
• Refers: ASTM F366-17 - Standard Specification for Fixation Pins and Wires
• Effective Date: 01-Sep-2017
• 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 F1264-16 - Standard Specification and Test Methods for Intramedullary Fixation Devices
• Effective Date: 01-May-2016
• Refers: ASTM F1264-16e1 - Standard Specification and Test Methods for Intramedullary Fixation Devices
• Effective Date: 01-May-2016
• 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 D790-15 - Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• Effective Date: 01-Dec-2015
• Refers: ASTM F366-10(2015) - Standard Specification for Fixation Pins and Wires
• Effective Date: 01-Mar-2015

Overview

ASTM F1541-17 is the international standard specification and test method for external skeletal fixation devices (ESFDs). Developed by ASTM International, this standard provides comprehensive guidelines for the design characterization, classification, terminology, material specifications, and performance assessment of ESFDs used in orthopedic surgery for fracture fixation and skeletal stabilization.

The key objective of ASTM F1541-17 is to create a consistent terminology and classification system for the wide range of ESFD configurations, as well as to define standard test methods for evaluating their mechanical properties. While not establishing specific performance thresholds or dictating particular device designs, this standard lays the foundation for both practitioners and manufacturers to assess and compare the functional characteristics of ESFDs.

Key Topics

• ESFD Terminology and Classification
  Establishes a standardized vocabulary for external fixators, their elements, and clinical configurations, enabling effective communication and documentation across the orthopedic community.

• Design Features and Elements
  Outlines basic ESFD geometrical definitions, dimensions, modularity, and component descriptions, covering anchorage elements (pins, screws, wires), bridge elements (rods, rings), and connectors.

• Material Specifications
  Provides references to suitable ASTM material standards for surgical implants, ensuring the compatibility and safety of used materials.

• Standard Test Methods
  Includes annexes detailing a range of test methods:

  • Connector stiffness and strength (Annex A2)
  • In-plane compressive properties of ring elements (Annex A3)
  • Joint performance (Annex A4)
  • Pin anchorage properties (Annex A5)
  • Subassembly and construct-level tests (Annexes A6, A7)

• Performance Measurement
  Focuses on reliable mechanical characterization (e.g., stiffness, strength, compliance) of external fixator components and subassemblies rather than case-specific outcomes.

• Safety Considerations
  Highlights the user’s responsibility to implement appropriate safety, health, and environmental practices, and to determine regulatory compliance.

Applications

ASTM F1541-17 serves as a critical resource in diverse applications within the orthopedic, trauma, and medical device sectors:

• Product Development & Quality Assurance
  Used by device manufacturers and engineers to design, test, and qualify new or modified external fixation devices against internationally accepted procedures and material standards.

• Comparative Device Assessment
  Enables healthcare professionals, procurement teams, and regulatory bodies to compare different ESFD products on a consistent mechanical basis through standardized terminology and test reports.

• Orthopedic Surgery Practice
  Assists surgeons and clinicians by providing device definitions and classifications that clarify the selection and documentation of appropriate external fixation systems for patient care.

• Research & Education
  Facilitates academic and clinical research on bone fixation, mechanical stability, and device innovation by providing robust testing frameworks.

Related Standards

For comprehensive device and material evaluations in orthopedic fixation, the following ASTM standards are often used in conjunction with ASTM F1541-17:

• ASTM F366 - Specification for Fixation Pins and Wires
• ASTM F543 - Specification and Test Methods for Metallic Medical Bone Screws
• ASTM D790 - Test Methods for Flexural Properties of Plastics and Insulating Materials
• ASTM E4 - Practices for Force Verification of Testing Machines
• ASTM F67, F90, F136, F138 - Material specifications for surgical implants
• ASTM F1264 - Specification and Test Methods for Intramedullary Fixation Devices

These related standards help ensure comprehensive quality, compatibility, and safety across a spectrum of orthopedic implants and surgical procedures.

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Keywords: ASTM F1541-17, external skeletal fixation devices, ESFD, orthopedic fixation, mechanical testing, device classification, orthopedic standards, fracture fixation devices, test methods for external fixators, ASTM standards for implants.

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:F1541 −17
Standard Specification and Test Methods for
External Skeletal Fixation Devices
This standard is issued under the fixed designation F1541; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.3.7 Test Method for External Skeletal Fixator/Constructs
Subassemblies—Annex A7.
1.1 This specification provides a characterization of the
design and mechanical function of external skeletal fixation 1.4 A rationale is given in Appendix X1.
devices (ESFDs), test methods for characterization of ESFD
1.5 The values stated in SI units are to be regarded as
mechanical properties, and identifies needs for further devel-
standard. No other units of measurement are included in this
opment of test methods and performance criteria.The ultimate
standard.
goal is to develop a specification, which defines performance
1.6 Multiple test methods are included in this standard.
criteria and methods for measurement of performance-related
However, the user is not necessarily obligated to test using all
mechanicalcharacteristicsofESFDsandtheirfixationtobone.
of the described methods. Instead, the user should only select,
It is not the intention of this specification to define levels of
with justification, test methods that are appropriate for a
performance or case-specific clinical performance of the
particular device design. This may be only a subset of the
devices, as insufficient knowledge is available to predict the
herein described test methods
consequences of the use of any of these devices in individual
patients for specific activities of daily living. Furthermore, it is
1.7 The following safety hazards caveat pertains only to the
not the intention of this specification to describe or specify test method portions (Annex A2 – Annex A6):
specific designs for ESFDs.
1.8 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.2 This specification describes ESFDs for surgical fixation
of the skeletal system. It provides basic ESFD geometrical responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
definitions, dimensions, classification, and terminology; mate-
rial specifications; performance definitions; test methods; and mine the applicability of regulatory limitations prior to use.
1.9 This international standard was developed in accor-
characteristics determined to be important to the in-vivo
performance of the device. dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
1.3 This specification includes a terminology and classifi-
Development of International Standards, Guides and Recom-
cationannexandfivestandardtestmethodannexesasfollows:
mendations issued by the World Trade Organization Technical
1.3.1 Classification of External Fixators—Annex A1.
Barriers to Trade (TBT) Committee.
1.3.2 Test Method for External Skeletal Fixator
Connectors—Annex A2.
2. Referenced Documents
1.3.3 Test Method for Determining In-Plane Compressive
2.1 ASTM Standards:
Properties of Circular Ring or Ring Segment Bridge
A938Test Method for Torsion Testing of Wire
Elements—Annex A3.
D790Test Methods for Flexural Properties of Unreinforced
1.3.4 Test Method for External Skeletal Fixator Joints—
and Reinforced Plastics and Electrical Insulating Materi-
Annex A4.
als
1.3.5 Test Method for External Skeletal Fixator Pin Anchor-
E4Practices for Force Verification of Testing Machines
age Elements—Annex A5.
F366Specification for Fixation Pins and Wires
1.3.6 Test Method for External Skeletal Fixator
F543Specification and Test Methods for Metallic Medical
Subassemblies—Annex A6.
Bone Screws
F544Reference Chart for Pictorial Cortical Bone Screw
This specification 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 September 2017. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
published as F1541 – 94. Last previous edition approved in 2015 as Standards volume information, refer to the standard’s Document Summary page on
F1541–02(2015). DOI: 10.1520/F1541-17. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1541−17
Classification (Withdrawn 1998) for evaluating the mechanical performance of ESFD connector
F1264Specification and Test Methods for Intramedullary elements is described in Annex A2.
Fixation Devices
6.2.2 ESFDs involving ring-type bridge elements are used
F2503Practice for Marking Medical Devices and Other widely both for fracture treatment and for distraction osteo-
Items for Safety in the Magnetic Resonance Environment
genesis. The anchorage elements in such fixators usually are
wires or thin pins, which pass transverse to the bone long axis
3. Terminology
andwhicharetensioneddeliberatelytocontrolthelongitudinal
3.1 Definitions—Thedefinitionsoftermsrelatingtoexternal stiffness of the fixator. Tensioning these wires or pins causes
fixators are described in Annex A1. appreciable compressive load in the plane of the ring element.
A test method for evaluating the mechanical performance of
4. Classification
ESFDringelementsinthisloadingmodeisdescribedinAnnex
A3.
4.1 Externalskeletalfixatorsaremodulardevicesassembled
from component elements. 6.2.3 ThehighloadsoftendevelopedatESFDjunctionsites
are of concern both because of potentially excessive elastic
4.2 Test methods can address individual elements (for
deformation and because of potential irrecoverable deforma-
example,anchorageelements,bridgeelements);subassemblies
tion. In addition to the connecting element itself (Annex A2),
ofelements(forexample,connectors,joints,ringelements);or
overall performance of the junction also depends on the
the entire fixator.
interface between the connecting element and the anchorage,
4.3 Tests of an entire assembled fixator may include the
or bridge elements, or both, which it grips. A test method for
fixator alone, or alternatively, the fixator as anchored to a
evaluating the overall strength, or stiffness, or both, at an
representation of the bone(s) upon which it typically would be
externalfixatorjoint,asdefinedinAnnexA1astheconnecting
mounted in clinical usage.
element itself plus its interface with the anchorage, or bridge,
or both, elements, which it grips, is described in Annex A4.
5. Materials
6.2.4 The modular nature of many ESFD systems affords
5.1 ESFD’s construction materials should be chosen based
thesurgeonparticularlygreatlatitudeastoconfigurationofthe
on the design requirements of the particular device. ASTM
frame subassembly, as defined in Annex A1 as the bridge
committeeF04onMedicalandSurgicalMaterialsandDevices
elements plus the connecting elements used to join bridge
maintains a number of material specifications suitable for
elements, but specifically excluding the anchorage elements.
surgical implant and instrument applications.
Since the configuration of the frame subassembly is a major
determinant of overall ESFD mechanical behavior, it is impor-
6. Performance Considerations and Test Methods
tant to have procedures for unambiguously characterizing
6.1 Individual Components—The anchorage pins by which
frame subassemblies, both geometrically and mechanically.
anESFDisattachedtoaskeletalmemberormemberstypically
Test methodology suitable for that purpose is described in
experience high flexural, or torsional loads, or both. Often, the
Annex A6.
majority of the overall compliance of an ESFD is in its
6.3 Entire Assembled Fixator—No test methods are yet
anchorageelements.Atestmethodforevaluatingthemechani-
approved for entire assembled fixators.
cal performance of an ESFD anchorage element in either of
these loading modes is described in Annex A5.
7. Handling
6.2 Subassemblies of Elements:
7.1 Consider Practice F2503 to identify potential hazards
6.2.1 The sites of junction between ESFD anchorage ele-
produced by interactions between the device and the MR
ments (for example, pins) and bridge elements (for example,
environmentandfortermsthatmaybeusedtolabelthedevice
rods) normally require specialized clamping or gripping
for safety in the MR environment.
members, known as connecting elements. Often, connecting
elements are subjected to high loads, especially moments, so
8. Keywords
adequacy of their intrinsic mechanical stiffness, or strength, or
both, is critical to overall fixator performance. A test method
8.1 anchorageelement;bending;bridgeelement;connector;
external skeletal fixation device; fracture fixation; joints;
modularity; orthopedic medical device; osteosynthesis; ring
The last approved version of this historical standard is referenced on
www.astm.org. element; subassembly (frame); terminology; torsion
F1541−17
ANNEXES
(Mandatory Information)
A1. CLASSIFICATION OF EXTERNAL SKELETAL FIXATORS
A1.1. Scope A1.5 Basis of Classification
A1.1.1 This classification covers the definitions of basic A1.5.1 An assembled ESFD and the bone(s) or bone ana-
terms and considerations for external skeletal fixation devices log(s) to which it is affixed constitute a fixator-bone construct.
(ESFDs) and the mechanical analyses thereof.
A1.5.1.1 The assembled ESFD itself, apart from the host
bone, is termed the fixator assembly.
A1.1.2 It is not the intent of this classification to define
A1.5.1.2 The individual parts (or modules of individual
levels of acceptable performance or to make recommendations
parts)fromwhichtheenduserassemblesthefixatoraretermed
concerning the appropriate or preferred clinical usage of these
its elements.
devices.
A1.5.2 AnESFDnormallyisconfiguredtospanamechani-
A1.1.3 This standard does not purport to address all of the
cal discontinuity in the host bone that otherwise would be
safety concerns, if any, associated with its use. It is the
unable to transmit one or more components of the applied
responsibility of the user of this standard to establish appro-
functional load successfully.This bony discontinuity is termed
priate safety, health, and environmental practices and deter-
the mechanical defect.
mine the applicability of regulatory limitations prior to use.
A1.1.4 This international standard was developed in accor-
A1.5.3 Examples of mechanical defects are fracture
dance with internationally recognized principles on standard-
surfaces, interfragmentary callus, segmental bone gaps, articu-
ization established in the Decision on Principles for the
lar surfaces, neoplasms, and osteotomies.
Development of International Standards, Guides and Recom-
A1.5.4 Coordinate System(s)—The relative positions of the
mendations issued by the World Trade Organization Technical
bones or bone segments bordering the mechanical defect
Barriers to Trade (TBT) Committee.
should be described in terms of an orthogonal axis coordinate
system (Fig. A1.1).
A1.2. Referenced Documents
A1.5.4.1 Where possible, coordinate axis directions should
A1.2.1 ASTM Standards:
be aligned perpendicular to standard anatomical planes (for
F366Specification for Fixation Pins and Wires
example,transverse(horizontaloraxial),coronal(frontal),and
F543Specification and Test Methods for Metallic Medical
sagittal (median)).
Bone Screws
A1.5.4.2 Where possible, translation directions should be
F544Reference Chart for Pictorial Cortical Bone Screw
consistent with standard clinical conventions (for example,
Classification (Withdrawn 1998)
ventral (anterior), dorsal (posterior), cranial (cephalad or
superior), caudal (inferior), lateral, or medial).
A1.3 Background
A1.5.4.3 Rotation measurement conventions must follow
A1.3.1 ESFDs are in widespread use in orthopedic surgery, the right-hand rule and, where possible, should be consistent
primarily for applications involving fracture fixation or limb with standard clinical terminology (for example, right or left
lengthening,orboth.Themechanicaldemandsplacedonthese lateral bending, flexion, extension, and torsion).
devices often are severe. Clinical success usually depends on
A1.5.5 Abase coordinate system (X, Y, Z) should be affixed
suitablemechanicalintegrationoftheESFDwiththehostbone
to one of the bones or major bone segments bordering the
or limb.
mechanical defect. This bone or bone segment is termed the
A1.3.2 It is important, therefore, to have broadly accepted base segment, S , and serves as a datum with respect to which
b
terminology and testing standards by which these devices can
pertinent motion(s) of bone segments or fixator elements, or
be described and their mechanical behaviors measured. both, can be referenced. Depending on context, S may be
b
defined as being on either the proximal or the distal side of a
A1.3.3 Useful terminology and testing standards must take
mechanical defect.
into account that the modular nature of most ESFDs deliber-
ately affords a great deal of clinical latitude in configuring the A1.5.6 The other bone(s) or bone segment(s) bordering the
assembled fixator. mechanical defect, whose potential motion(s) with respect to
S is of interest, is termed the mobile segment(s), S.If
b m
A1.4. Significance and Use necessary, a local right-handed orthogonal coordinate system
(x, y, z) may be embedded within the S (s).
m
A1.4.1 The purpose of this classification is to establish a
consistent terminology system by means of which these ESFD A1.5.7 Degrees of Freedom: Describing the position, or
configurations can be classified. It is anticipated that a com- change in position, of S relative to S requires specifying one
m b
panion testing standard using this classification system will ormoreindependentvariables.Thesevariablesshallbetermed
subsequently be developed. positional degrees of freedom (P-DOF).
F1541−17
given the clinical name “dynamization,” will be termed un-
locked degrees of freedom (U-DOF).
A1.5.9.1 Depending on the specifics of design, the motion
permitted in an unlocked degree of freedom may be opposed
substantially and deliberately by a specific mechanism such as
a spring or a cushion. Such an unlocked degree of freedom is
termed a resisted unlocked degree of freedom.
A1.5.9.2 Unlocked degrees of freedom in which motion is
induced actively by external energy input from devices asso-
ciatedwiththefixatoraretermed actuateddegreesoffreedom.
A1.5.9.3 Anunlockeddegreeoffreedominwhichmotionis
unopposed by a specific design mechanism is termed an
unresisted unlocked degree of freedom. Incidental friction in a
dynamizing element shall not be construed as representing
deliberately resisted motion; however, conditions involving
untoward resistance to motion, for example, substantial bind-
ing friction, in a supposedly unresisted degree of freedom
should be identified.
A1.5.10 For adjustment or unlocked DOFs, the extrema of
angular or translational displacement between which motion is
permitted before encountering a fixed or adjustable constraint
are termed that DOF’s range of motion (ROM).
A1.5.11 A fixator assembly consists of a structurally pur-
poseful arrangement of three basic types of elements: bone
anchorage elements, usually transcutaneous; bridge elements,
usually extracutaneous; and connection elements.
S = base segment
b
A1.5.12 Anchorage elementsarethosethatattachdirectlyto
S = mobile segment
m
D = mechanical defect the bone. Examples are smooth pins, threaded pins, screws,
O = origin of base reference frame
wires, or cortex clamps.
X, Y, and Z = base reference frame axes
o = origin of mobile reference frame A1.5.13 Bridge elements are structural members designed
x, y, and z = mobile reference frame axes
to transmit loads over relatively long distances, and they are
R = transverse rod
t
joined to one another or to anchorage elements, or both, by
R = longitudinal rod
L
P =pin
connectors. Bridge elements can either be simple or complex
C = rod-rod connector
rr
and should be described in terms of their characteristic shape
C = pin-rod connector
pr
and, where appropriate, their orientation with respect to the
FIG. A1.1External Fixator Definition Schematic bone or the mechanical defect.
A1.5.13.1 Examples of simple bridge elements are longitu-
dinal rods, transverse rods, rings, or ring segments. Simple
A1.5.7.1 Depending on context, this may involve as many
bridge elements need not be single-piece. If multipiece,
as six variables (three translation and three orientation).
however, the individual parts are joined rigidly rather than
A1.5.7.2 Also depending on context, P-DOFs may be used
adjustable by the end user.
to describe motions of interest in various magnitude ranges.
A1.5.13.2 Complex bridge elements are mechanisms that
For example, P-DOFs may be used to describe one or more
consist of two or more subelements designed to function
components of visually imperceptible motion (for example,
togethertoachieveaspecifickinematicobjective.Examplesof
elastic flexure of a thick rod) or one or more components of
complex bridge elements are articulated or telescoping mecha-
grossly evident motion (such as interfragmentary motion at an
nisms.
unstable fracture site).
A1.5.14 Connectors join bridge elements either to other
A1.5.8 Application or adjustment of an ESFD normally bridgeelementsortoanchorageelements.Ofthetwoelements
includesanattempttoachieveormaintainaspecificpositionof
comprising any joint or junction, the connector is that element
S relative to S . The adjustability afforded by the ESFD towhichtheenduserappliesanactivegrippingforceortorque
m b
design for this purpose, most commonly, fracture fragment
to engage the attachment. Connectors should be described in
reduction,willbecharacterizedintermsof adjustment degrees terms of the types of elements that they connect and, where
of freedom (A-DOF).
appropriate, in terms of their adjustment or unlocked degrees
of freedom. Examples of connectors are pin(-rod) clamps, pin
A1.5.9 Some ESFDs are designed optionally to transmit
cluster(-rod) clamps, ring-rod clamps, and rod-rod clamps.
selected components of loading or displacement across the
defect, usually by disengaging a locking mechanism. The A1.5.15 That portion of the fixator assembly specifically
componentofmotionof S permittedbysuchunlocking,often excluding the bony anchorage elements and their associated
m
F1541−17
connectors is termed the frame. Connectors that join only A1.6.1.4 Cortexclamps(claws/prongs)areanchorsthatgrip
bridge elements, or that join bridge elements to bone anchors the host bone externally at two or more sites, without penetrat-
but are not user removable from bridge elements, are consid- ing through the full cortical thickness. Cortex clamps may or
ered to be part of the frame. may not pierce the periosteum.
A1.5.16 Ajoint or junction for which the relative positions A1.6.2 Frame bridge elements are structural members con-
betweenanytwoelementsorsubelementscanbecontrolledby figuredinsuchamannerastotransmitfunctionalloadfromthe
the end user is termed an articulation. The components of anchorage elements on one side of the mechanical defect to
relative motion permitted between the fixator elements at an those on the other side of the defect. Bridge elements can be
articulation should be described in terms of that articulation’s simple members such as smooth prismatic rods, threaded rods,
degrees of freedom, either A-DOF or U-DOF, depending on bars, flat plates, curved plates, or arched plates. Alternatively,
context. Additionally, articulations should be described in they can be complex assemblies of several members, designed
terms of the types of elements that they connect. to allow or induce specific motions such as fixed axis rotation,
linear sliding, or active adjunct distraction. Most ESFD frames
A1.5.17 Joints at which the relative positions of the ele-
using simple bridge elements involve structural arrangements
ments connected are fixed and cannot be controlled by the end
in which several simple bridge elements are linked to one
user are termed nonadjustable. Nonadjustable joints should be
another by connectors.
described in terms of the types of elements that they connect.
A1.6.3 Fixator-Bone Construct Classifications—Constructs
A1.6 Attributes
may be classified in accordance with the anatomic skeletal
structure to which the frame is applied. Common types are as
A1.6.1 Coupling between the assembled frame and the host
follows:
bone is achieved by anchorage elements such as wires, pins
A1.6.3.1 Long bone,
(threaded or unthreaded), screws, or cortex clamps (sometimes
A1.6.3.2 Articular joint,
called claws or prongs). In long bone applications, anchorage
A1.6.3.3 Pelvis,
elements normally transmit load transversely from the host
A1.6.3.4 Spinal, and
bone segments to the frame structure.
A1.6.3.5 Halo (skull).
A1.6.1.1 Wires are thin, smooth, constant cross-section
A1.6.3.6 A construct subunit is one bony fragment plus its
(usually circular) anchorage elements that transmit load from
pins/wires and connectors and plus bridge elements not shared
thehostbonetotheframeprimarilybyaxialtensionasaresult
with other bony fragments.
of transverse (“bow string”) distention by the host bone;
therefore,wiresmusttransfixtheboneandmustbeclampedto
A1.6.4 Long bone frames or frame subunits can be charac-
the frame at two sites. The stiffness of bone-frame coupling
terized in terms of limb access.
achievedusingawiredependssensitivelyonthetensioninthe
A1.6.4.1 Frames or frame subunits that encompass 90° or
wire, which normally is controlled by the end user. Stoppers
less of an extremity sector circumferentially are termed unilat-
(“olives”) sometimes are used to oppose incidental slippage
eral.
along the length of a transfixing wire.
A1.6.4.2 Frames or frame subunits that encompass more
A1.6.1.2 Pins are slender anchorage elements, again, usu-
than 90° of an extremity sector circumferentially are termed
ally of circular cross section or envelope, for which bone-to-
multilateral.Multilateralframesareoftendescribedintermsof
frame load transmission occurs primarily by longitudinal
their characteristic geometry: bilateral (two columns of longi-
bending stresses. Pins can penetrate one or (usually) both
tudinal bridge elements), triangular (three longitudinal
cortices of a long bone, and they can be clamped to the frame
columns), quadrilateral (four columns), or circular (ring fix-
at one end (“half-pins”) or both ends (“through-and-through
ators).
pins” or “full-pins”). Pins can either be smooth or threaded.
A1.6.5 Long bone frames or frame subunits (unilateral or
Threaded pins can be designed for achieving purchase in
multilateral)canbeclassifiedaccordingtopinconfiguration,as
cortical bone, cancellous bone, or in a combination of the two.
follows:
Pins can either be of constant cross section, shouldered, or
A1.6.5.1 As one plane if all of their pins lie approximately
tapered. They can be clamped to the frame either individually
within a common plane,
orinclusters.Dependingonthefluteorthreaddesign,orboth,
A1.6.5.2 Or as multiplane if their pins lie in two or more
pins can be classified as being one of the following:
distinct planes.
(1)Self-drilling/self-tapping,
(2)Self-tapping/nonself-drilling, or A1.6.6 Constructs may be classified in terms of the means
(3)Nonself-tapping/nonself-drilling. by which the frame is coupled to the bone.
A1.6.1.3 Screws are threaded anchorage elements, loaded A1.6.6.1 A frame for which coupling to the bone is by a
primarily in axial tension or in transverse shear, or both. This homogeneousgroupofprimarilymoment-transmittinganchors
term is sometimes (mis)used interchangeably as a descriptor such as pins, screws, or cortex claws is termed a pin-fixed
for ESFD threaded pins, but it is reserved more properly for construct.
devices that have a head with a recess for wrenching (see A1.6.6.2 Ifthecouplingisbyprimarilytension-transmitting
Specification F543 and Reference Chart F544) and that are members instead, the construct is said to be wire fixed. The
used to develop compression across a fracture site or across a wire-fixed constructs involve ring-type bridge elements in
bone/implant interface. almost all instances.
F1541−17
A1.6.6.3 If coupling involves a heterogeneous mixture of A1.6.8 Somepin-fixedconstructsallowindependentcontrol
wires and pins (or screws or other anchorage elements, or of each pin’s orientation and DOF of articulation with the
both), the construct is said to incorporate hybrid coupling.
frame.Inotherdesigns, multipin clampsareusedtocontrolthe
common orientation and DOF of frame articulation of a small
A1.6.7 Fixatorconstructsmaybeclassifiedaccordingtothe
group of pins termed a pin cluster. Pin cluster clamps most
degree of homology or similarity between the respective
commonly enforce parallel alignment of the pins in the cluster.
subunits.
The specific A-DOF and U-DOF of pin/frame articulation in
A1.6.7.1 If the bone fragments on opposing sides of a
each instance, that is, either independent or clustered pins,
mechanical defect are part of analogously assembled construct
subunits, the overall fixator is said to be symmetrically config- depends on the design of the specific connecting element
ured. This does not imply strict geometric symmetry about the joining the pin(s) to the frame.
defect mid plane, but rather that each major element in each
A1.6.9 Ring fixators have complex frames assembled from
construct subunit possesses a similar counterpart in the other
several transverse-plane ring or partial-ring bridge elements.
construct subunit.
The anchoring transfixation tensile wires are connected to the
A1.6.7.2 A construct whose subunits do not have such
rings individually. Longitudinal rods normally are used to
counterpart elements is said to have a hybrid,or asymmetri-
connect the transverse-plane rings.
cally configured, frame.
A2. TEST METHOD FOR EXTERNAL SKELETAL FIXATOR CONNECTORS
A2.1. Scope (2)Connectorsshouldbedescribedintermsofthetypesof
elements, which they connect, and where appropriate, in terms
A2.1.1 Thistestmethodcoverstheproceduresfordetermin-
of their adjustment or unlocked degrees of freedom.
ing the stiffness and strength of connecting elements (clamps)
(3)Examples of connectors are pin(-rod) clamps, pin
of external skeletal fixators under axial loads and bending
cluster(-rod) clamps, ring-rod clamps, and rod-rod clamps.
moments.Dependingonthedesignoftheconnectoranditsuse
A2.3.1.2 input-loading axis—the line of application in the
in the overall construct, the connector needs to transmit one or
case of a force input, or the axis about which a moment is
more components of loading (tension, compression, torsion, or
applied in the case of a moment input.
bending, or a combination thereof) between the elements it
grips (anchorage elements or bridge elements), without itself
A2.3.1.3 input-loading platen—a member, not normally
undergoing either permanent deformation or excessive elastic
part of the connector during clinical usage, through which the
deformation.
input force, or moment, is delivered from the testing machine
actuator to the connector.
A2.1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
A2.3.1.4 support platen—a member, also not normally part
responsibility of the user of this standard to establish appro-
of the connector during clinical usage, through which the
priate safety, health, and environmental practices and deter-
connector is rigidly affixed to the testing machine base.
mine the applicability of regulatory limitations prior to use.
A2.4. Summary of Test Method
A2.1.3 This international standard was developed in accor-
dance with internationally recognized principles on standard-
A2.4.1 Connecting elements (clamps) are obtained, and if
ization established in the Decision on Principles for the
applicable, assembled using the techniques and equipment
Development of International Standards, Guides and Recom-
recommended by the manufacturer. Platens substituting for the
mendations issued by the World Trade Organization Technical
body, or anchorage elements, or both, are attached to the
Barriers to Trade (TBT) Committee.
connector in such a manner that no slippage can occur relative
to the connector. Axial loads or bending moments are applied
A2.2. Referenced Documents
to the connector, and a graphical plot of load (or moment)
A2.2.1 ASTM Standards:
versus displacement is used to determine the intrinsic stiffness,
E4Practices for Force Verification of Testing Machines
and strength, if tested to failure, of the connector.
A2.3. Terminology
A2.5. Significance and Use
A2.3.1 Definitions of Terms Specific to This Standard: A2.5.1 These laboratory benchtop tests are used to deter-
A2.3.1.1 connectors—external fixator elements used to join mine values for the intrinsic stiffness, or strength, or both, of
bridge elements either to other bridge elements, or to anchor- connectors, under force or moment loadings. Since different
age elements. connectors have different materials and geometries, stresses
(1)Of the two elements comprising any joint or junction, within individual subcomponents or at subcomponent inter-
the connector is that element to which the end user applies an faces may differ substantially between designs. During testing,
active gripping force or torque to engage the attachment. the connectors are loaded and supported in such a manner that
F1541−17
all measured deformation occurs within the connector itself,
rather than at the interface between the connector and the
fixator element(s) gripped.
A2.5.2 The results obtained in this test method are not
intended to predict the clinical efficacy or safety of the tested
elements. This test method is intended only to measure the
uniformityoftheelementstestedortocomparethemechanical
performance of different connectors; however, the actual load
that can be transmitted to the connector in clinical practice
depends very much on the slippage resistance of the different
subcomponent interfaces.
A2.5.3 Thistestmethodmaynotbeappropriateforalltypes
of external skeletal fixator applications. The user is cautioned
to consider the appropriateness of the method in view of the
materials and designs being tested and their potential applica-
tion.
A2.6. Apparatus
A2.6.1 Force or Moment or both Application Fixture:
A2.6.1.1 The loading configuration is shown schematically
in Fig.A2.1. The input loading axis must pass through one of
A = local coordinate system, defined with respect to land-
theplatens(theloadingplaten)rigidlyaffixedtotheconnector.
mark Point O
The other platen (the support platen) is rigidly affixed to the
B = rod (as normally gripped by connector)
C = connector body
base of the testing apparatus.
D = connector tightening mechanism(s)
A2.6.2 Load Frame—Machines used for testing shall con-
E = rod grip platen (support platen)
G = rod grip interface
form to the requirements of Practices E4. The loads used for
H = pins (as normally gripped by connector)
this test method shall be within the loading range of the test
J = pin grip/clamp platen (loading input platen, rigidly
machine as defined in Practices E4.
bonded to pin grip)
K = pin clamping interface
A2.6.3 DataAcquisition Device—Asuitablerecordertoplot
L = pin grip/clamp tightening mechanism
M = testing machine base (fixed)
agraphofloadversusloadframedisplacementonperpendicu-
N = pin grip/clamp (in this illustration, the input loading is a
lar axes. Optionally, this device may include the use of
force Fz*inthe z* direction, delivered through a loading
computer-based digital sampling and output of the load and
platen rigidly affixed to the pin grip/clamp. δ is the dis-
z
placement of the loading platen in the z direction
displacement signals.
FIG. A2.1Schematic for Testing an External Fixator Connector
A2.7. Test Specimen
(Example, Generic for a Pin-Rod Joint)
A2.7.1 All tested connectors should be representative of
clinical quality products.
are intrinsic to the connecting element itself and are not
A2.7.2 If the connector(s) to be tested have been used
influenced by possible interfacial slippage between the con-
previously, the nature of such prior usage should be described
necting element and the fixator elements (for example, rods or
appropriately.
anchorage pins) which it clamps.
A2.7.3 Thetestspecimensshouldbepreparedinthemanner
(1)The input and support platens should made of steel or
in which they would normally be used clinically. For example,
other metal and should have negligible compliance relative to
if a particular connector would normally be sterilized in a
that of the connecting element itself.
particular manner before clinical use, it should be similarly
(2)The input and support platens should have recesses to
sterilized before mechanical testing.
accommodate those fixator elements geometrically, for
A2.7.4 If the connector to be tested is a prototype, or under
example, anchorage pins or rods, normally clamped by the
development, or both, the geometric and material information
connecting element being tested.
needed to characterize the component fully should either be
(3)The input and support platens should be rigidly affixed
included in the report, or detailed descriptive information
to the connecting element (for example, by welding, epoxy,
should be referenced.
cyanoacrylate cement, or other appropriate means).
A2.8.1.2 Theinputandsupportplatensserveasattachments
A2.8. Procedure
for gripping by the testing apparatus. This test method is
A2.8.1 Configuring the Connecting Element for Testing: applicable only to those components of loading (force or
A2.8.1.1 With the connecting element assembled in the moment, or both), which can be applied through such platens.
configuration normally used, input and support platens are A2.8.1.3 Alocalright-handedcoordinatesystem(X*,Y*,Z*)
affixedinamannerthatinsuresthatallmeasureddeformations should be defined with respect to a specific origin landmark
F1541−17
point on (or in) the connecting element. The platen locations elastic range, approximately 50% of the expected physiologic
(position and orientation) should be identified relative to these service load or 50% of the expected connector failure load,
local coordinate axes. whichever is lower.
A2.8.7.3 Load/deformation curves for the preconditioning
A2.8.2 Mounting the Test Connector:
cycles should be recorded. Preconditioning cycle stiffnesses
A2.8.2.1 The platen through which the input force (or
should be reported.
moment) is to be applied is gripped, appropriately aligned, in
A2.8.8 Data Recording—The load (N) or torque (N-m) and
the testing machine.The support platen is rigidly affixed to the
linear (mm) or angular (°) displacement measured by the
testing machine base.
testing machine should be continuously recorded. The linear
A2.8.2.2 The grips and the testing machine itself should be
displacement should be measured at the point of load applica-
sufficiently stiff that their deformation under load is negligible
tion. In some instances it may be appropriate also to record
relativetothatoftheconnectingelementbeingtested.Thetare
components of deformation in directions other than that of the
compliance of the testing machine and grips, that is, without
appliedloading.Ifso,thesensorsused,forexample,dialgages
the connector mounted, should be measured and reported.
or linear variable differential transducers (LVDTs), and the
Typically,thetarecomplianceofthetestingmachineplusgrips
pointsanddirectionsoftheirmeasureddeformationsshouldbe
should be less than 1% of the compliance of the connector
recorded.
being tested. The gripping mechanism should be clearly
described.
A2.9. Calculation or Interpretation of Results
A2.8.3 Forces should be delivered through an input platen,
A2.9.1 Stiffness (units according to the chosen load and
which is rigidly bonded to the connector. Normally, the axis of
deflection configuration, for example, N/mm for force, N-mm/
loadingwillbereferencedtothatofamember,suchasarodor
degree for moment) shall be calculated from the slope of the
a pin, that would be clamped by the connector. The line of
linear-most portion of the load/deflection curve, as apparent
actionoftheinputforceshouldberecordedrelativetothelocal
visually (Fig. A2.2, Point A). If an objective slope determina-
coordinate system. Appropriate fixturing detail should be
tiontechnique,forexample,curvefittingofadigitizedtracing,
provided as to how that force is applied through the input
is used, this should be described. The load and deflection
platen.
configuration (location of measuring element and direction of
A2.8.4 Moments may be delivered either by an eccentri-
themeasuredvector)shallbedefinedclearlywithrespecttothe
cally applied force, or alternatively, by a torsional actuator. In loading axis of the testing equipment (Fig. A2.1).
theformerinstance,theoffsetfromthelocalcoordinatesystem
A2.9.2 Failure load (N or N-mm) of the connector is
origin should be recorded. In either instance, the orientation of
frequently associated with a discontinuity in the load/
the moment axis should be recorded relative to the local
coordinate system.Appropriate fixturing details as to how that
momentisappliedthroughtheinputplatenshouldbeprovided.
A2.8.5 For connectors made entirely of metal or other
materialsexhibitingelasticbehavior,theload(ormoment)may
be applied quasistatically. An input rate sufficient to attain in
30-s force, or moment, magnitude in the range of typical
clinical usage, or of connector failure, shall be deemed
quasistatic. For connectors incorporating polymeric or other
materials that exhibit viscoelastic behavior, load/stroke rates,
whichareintherangeofthoseexpectedclinically,mayinstead
be desirable. In either case, the rate(s) used and a rationale for
its choice should be provided.
A2.8.6 Tests may be run under either load or displacement
control. They may either be single- or multi-cycle, and can be
either restricted to the elastic regime, or taken to failure of the
connector. The specific conditions used should be described
fully.
A2.8.7 If single-cycle testing is to be performed, the speci-
men shall be subjected to several preconditioning load cycles
to demonstrate that the reported load/deformation curve is
repeatable from cycle to cycle.
NOTE 1—Stiffness is defined as the slope of the linear-most portion of
thecurve,hereevaluatedbyatangentdrawnatPointA.PointBillustrates
A2.8.7.1 Preconditioning should be continued until the
a slope discontinuity (possibly indicative of interfacial slip or subcompo-
apparent stiffness of the connector changes less than 5%
nentfailurewithintheconnector),andPointCillustratesthemaximalload
between subsequent cycles.
acceptance (ultimate strength).
A2.8.7.2 Normally, about five preconditioning load cycles
FIG. A2.2Load/Deformation Curve (Generic, Here Illustrated for
are suitable for this purpose, with peak applied load within the the z* Direction)
F1541−17
deformation curve. Depending on context, additional load A2.10.1.6 Loadingrateandnumberofcycles(fatiguetests).
uptake may or may not be possible after occurrence of this
A2.10.1.7 Stiffness, and, if loaded to failure, the failure
discontinuity. In the former circumstance (Fig.A2.2, Point B),
criterion and strength, in the specific direction(s) tested.
theseverityofthediscontinuityshouldbemeasuredintermsof
A2.10.1.8 In cases in which the mode of failure is
change in slopes of the load/deformation curve for loads
ascertainable, for example, visually apparent interfacial slip-
immediately below and above the discontinuity point. In the
page of a specific subcomponent interface, the nature of such
lattercircumstance(Fig.A2.2,PointC),thefailureloadshould
failure should be described.
be designated as the ultimate strength of the connector.
A2.9.3 In situations in which there is no clear discontinuity
A2.11. Precision and Bias
intheloaddisplacementcurve,otherdefinitionsoffailureload
A2.11.1 Data establishing the precision and bias to be
may be used.
expected from this test method have not yet been obtained.
A2.9.3.1 For situations in which permanent deformation
occurs, for example, as a result of interfacial slip or plastic
A2.12. Keywords
deformation, or both, within the connector, an offset criterion
may be used. In this instance, the failure load is defined as that
A2.12.1 bending moments; connecting elements; connec-
load necessary to induce a specific amount of permanent
tors; external fixator; orthopedic device; stiffness; strength
deformation, either linear or angular, depending upon the
degree of freedom being tested, upon release of the applied
A2.13 Rationale
load.
A2.13.1 Connecting elements of various designs are used
A2.9.3.2 For situations in which excessive elastic deforma-
widely in external fixators. Both the connected elements and
tion occurs within the connector, failure may be defined in
the pertinent directions of force (or moment, or both) trans-
terms of a specific fractional reduction of the connector’s
mission through them are design- and site-specific. This test
small-load stiffness. For example, failure might be defined in
termsoftheconnector’stangentstiffnesshavingfallento25% method provides an outline by which the stiffness, or strength,
of the tangent stiffness that was apparent at a load of 50 N. or both, intrinsic to the connector itself, as opposed to the
stiffness or strength by which it grips the elements it connects,
A2.10. Report
can be measured. Since the joints of external fixators normally
A2.10.1 The test report shall include, but is not limited to,
involve abrupt redirection of appreciable loads, substantial
the following information:
stresses often are developed within one or more of the
A2.10.1.1 Connecting Element Identification, including
subcomponents of the connector securing the joint.
manufacturer, part number, nomenclature, and quality control
A2.13.2 Even if there is no apparent interfacial slippage
or lot number. If the part is a prototype, geometrical and
between the connector and the various bridge or anchorage
material descriptions shall be included.
elementsitgrips,theassociatedelasticdeformationswithinthe
A2.10.1.2 Specimen preparation condition, for example,
connector body itself may result in appreciable distension of
sterilization and description of prior usage history, if appli-
the overall frame. Moreover, excessive forces, or more
cable.
commonly, moments, applied to a connector may cause de-
A2.10.1.3 Connecting force or torque used to engage the
structive failure of the connector body, even if gripped inter-
connector’s gripping mechanism.
faces remain intact. This test method focuses on the intrinsic
A2.10.1.4 Configuration of the (bonded) platens and testing
load/deformation behavior of the connector body, independent
apparatus grips.
ofwhetherornotthereisinterfacialslipbetweentheconnector
A2.10.1.5 Specific degrees of freedom tested, such as,
tension or compression, torsion, or bending. In each case, the and the bridge or anchorage elements, or both, which it grips.
axis along which or about which loading is applied should be This goal is achieved by means of platens, which are bonded
specified. rigidly to the connector.
F1541−17
A3. TEST METHOD FOR DETERMINING IN-PLANE COMPRESSIVE PROPERTIES OF CIRCULAR RING OR RING SEG-
MENT BRIDGE ELEMENTS
A3.1. Scope predict the clinical efficacy or safety of the tested products.
This test method is intended only to measure the uniformity of
A3.1.1 This test method covers the test procedure for
the products tested or to compare the mechanical properties of
determining the in-plane compressive properties of circular or
different products.
ring segment bridge elements of external skeletal fixators.
A3.5.2 Thistestmethodmaynotbeappropriateforalltypes
A3.1.2 This standard does not purport to address all of the
of fixator applications. The user is cautioned to consider the
safety
...

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: F1541 − 02 (Reapproved 2015) F1541 − 17
Standard Specification and Test Methods for
External Skeletal Fixation Devices
This standard is issued under the fixed designation F1541; 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 provides a characterization of the design and mechanical function of external skeletal fixation devices
(ESFDs), test methods for characterization of ESFD mechanical properties, and identifies needs for further development of test
methods and performance criteria. The ultimate goal is to develop a specification, which defines performance criteria and methods
for measurement of performance-related mechanical characteristics of ESFDs and their fixation to bone. It is not the intention of
this specification to define levels of performance or case-specific clinical performance of the devices, as insufficient knowledge is
available to predict the consequences of the use of any of these devices in individual patients for specific activities of daily living.
Furthermore, it is not the intention of this specification to describe or specify specific designs for ESFDs.
1.2 This specification describes ESFDs for surgical fixation of the skeletal system. It provides basic ESFD geometrical
definitions, dimensions, classification, and terminology; material specifications; performance definitions; test methods; and
characteristics determined to be important to the in-vivo performance of the device.
1.3 This specification includes a terminology and classification annex and five standard test method annexes as follows:
1.3.1 Classification of External Fixators—Annex A1.
1.3.2 Test Method for External Skeletal Fixator Connectors—Annex A2.
1.3.3 Test Method for Determining In-Plane Compressive Properties of Circular Ring or Ring Segment Bridge Elements—
Annex A3.
1.3.4 Test Method for External Skeletal Fixator Joints—Annex A4.
1.3.5 Test Method for External Skeletal Fixator Pin Anchorage Elements—Annex A5.
1.3.6 Test Method for External Skeletal Fixator Subassemblies—Annex A6.
1.3.7 Test Method for External Skeletal Fixator/Constructs Subassemblies—Annex A7.
1.4 A rationale is given in Appendix X1.
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 Multiple test methods are included in this standard. However, the user is not necessarily obligated to test using all of the
described methods. Instead, the user should only select, with justification, test methods that are appropriate for a particular device
design. This may be only a subset of the herein described test methods
1.7 The following safety hazards caveat pertains only to the test method portions (Annex A2 – Annex A6):
1.8 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.
1.9 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:
A938 Test Method for Torsion Testing of Wire
This specification 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 Sept. 1, 2015Sept. 1, 2017. Published October 2015September 2017. Originally published as F1541 – 94. Last previous edition approved in
ε1
20112015 as F1541 – 02 (2011)(2015). . DOI: 10.1520/F1541-02R15.10.1520/F1541-17.
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
F1541 − 17
D790 Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
E4 Practices for Force Verification of Testing Machines
F67 Specification for Unalloyed Titanium, for Surgical Implant Applications (UNS R50250, UNS R50400, UNS R50550, UNS
R50700)
F90 Specification for Wrought Cobalt-20Chromium-15Tungsten-10Nickel Alloy for Surgical Implant Applications (UNS
R30605)
F136 Specification for Wrought Titanium-6Aluminum-4Vanadium ELI (Extra Low Interstitial) Alloy for Surgical Implant
Applications (UNS R56401)
F138 Specification for Wrought 18Chromium-14Nickel-2.5Molybdenum Stainless Steel Bar and Wire for Surgical Implants
(UNS S31673)
F366 Specification for Fixation Pins and Wires
F543 Specification and Test Methods for Metallic Medical Bone Screws
F544 Reference Chart for Pictorial Cortical Bone Screw Classification (Withdrawn 1998)
F1058 Specification for Wrought 40Cobalt-20Chromium-16Iron-15Nickel-7Molybdenum Alloy Wire, Strip, and Strip Bar for
Surgical Implant Applications (UNS R30003 and UNS R30008)
F1264 Specification and Test Methods for Intramedullary Fixation Devices
F1472F2503 Specification for Wrought Titanium-6Aluminum-4Vanadium Alloy for Surgical Implant Applications (UNS
R56400)Practice for Marking Medical Devices and Other Items for Safety in the Magnetic Resonance Environment
F1713 Specification for Wrought Titanium-13Niobium-13Zirconium Alloy for Surgical Implant Applications (UNS R58130)
3. Terminology
3.1 Definitions—The definitions of terms relating to external fixators are described in Annex A1.
4. Classification
4.1 External skeletal fixators are modular devices assembled from component elements.
4.2 Test methods can address individual elements (for example, anchorage elements, bridge elements); subassemblies of
elements (for example, connectors, joints, ring elements); or the entire fixator.
4.3 Tests of an entire assembled fixator may include the fixator alone, or alternatively, the fixator as anchored to a representation
of the bone(s) upon which it typically would be mounted in clinical usage.
5. Materials
5.1 All ESFDs made of materials that have an ASTM standard shall meet those requirements given in ASTM Standards listed
inESFD’s construction materials should be chosen based on the design requirements of the particular device. ASTM committee
F04 on Medical and Surgical Materials and Devices maintains a 2.1.number of material specifications suitable for surgical implant
and instrument applications.
6. Performance Considerations and Test Methods
6.1 Individual Components—The anchorage pins by which an ESFD is attached to a skeletal member or members typically
experience high flexural, or torsional loads, or both. Often, the majority of the overall compliance of an ESFD is in its anchorage
elements. A test method for evaluating the mechanical performance of an ESFD anchorage element in either of these loading modes
is described in Annex A5.
6.2 Subassemblies of Elements:
6.2.1 The sites of junction between ESFD anchorage elements (for example, pins) and bridge elements (for example, rods)
normally require specialized clamping or gripping members, known as connecting elements. Often, connecting elements are
subjected to high loads, especially moments, so adequacy of their intrinsic mechanical stiffness, or strength, or both, is critical to
overall fixator performance. A test method for evaluating the mechanical performance of ESFD connector elements is described
in Annex A2.
6.2.2 ESFDs involving ring-type bridge elements are used widely both for fracture treatment and for distraction osteogenesis.
The anchorage elements in such fixators usually are wires or thin pins, which pass transverse to the bone long axis and which are
tensioned deliberately to control the longitudinal stiffness of the fixator. Tensioning these wires or pins causes appreciable
compressive load in the plane of the ring element. A test method for evaluating the mechanical performance of ESFD ring elements
in this loading mode is described in Annex A3.
6.2.3 The high loads often developed at ESFD junction sites are of concern both because of potentially excessive elastic
deformation and because of potential irrecoverable deformation. In addition to the connecting element itself (Annex A2), overall
performance of the junction also depends on the interface between the connecting element and the anchorage, or bridge elements,
The last approved version of this historical standard is referenced on www.astm.org.
F1541 − 17
or both, which it grips. A test method for evaluating the overall strength, or stiffness, or both, at an external fixator joint, as defined
in Annex A1 as the connecting element itself plus its interface with the anchorage, or bridge, or both, elements, which it grips,
is described in Annex A4.
6.2.4 The modular nature of many ESFD systems affords the surgeon particularly great latitude as to configuration of the frame
subassembly, as defined in Annex A1 as the bridge elements plus the connecting elements used to join bridge elements, but
specifically excluding the anchorage elements. Since the configuration of the frame subassembly is a major determinant of overall
ESFD mechanical behavior, it is important to have procedures for unambiguously characterizing frame subassemblies, both
geometrically and mechanically. Test methodology suitable for that purpose is described in Annex A6.
6.3 Entire Assembled Fixator—No test methods are yet approved for entire assembled fixators.
7. Handling
7.1 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.
8. Keywords
8.1 anchorage element; bending; bridge element; connector; external skeletal fixation device; fracture fixation; joints;
modularity; orthopedic medical device; osteosynthesis; ring element; subassembly (frame); terminology; torsion
ANNEXES
(Mandatory Information)
A1. CLASSIFICATION OF EXTERNAL SKELETAL FIXATORS
A1.1. Scope
A1.1.1 This classification covers the definitions of basic terms and considerations for external skeletal fixation devices (ESFDs)
and the mechanical analyses thereof.
A1.1.2 It is not the intent of this classification to define levels of acceptable performance or to make recommendations concerning
the appropriate or preferred clinical usage of these devices.
A1.1.3 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.
A1.1.4 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.
A1.2. Referenced Documents
A1.2.1 ASTM Standards:
F366 Specification for Fixation Pins and Wires
F543 Specification and Test Methods for Metallic Medical Bone Screws
F544 Reference Chart for Pictorial Cortical Bone Screw Classification (Withdrawn 1998)
A1.3 Background
A1.3.1 ESFDs are in widespread use in orthopedic surgery, primarily for applications involving fracture fixation or limb
lengthening, or both. The mechanical demands placed on these devices often are severe. Clinical success usually depends on
suitable mechanical integration of the ESFD with the host bone or limb.
A1.3.2 It is important, therefore, to have broadly accepted terminology and testing standards by which these devices can be
described and their mechanical behaviors measured.
F1541 − 17
A1.3.3 Useful terminology and testing standards must take into account that the modular nature of most ESFDs deliberately
affords a great deal of clinical latitude in configuring the assembled fixator.
A1.4. Significance and Use
A1.4.1 The purpose of this classification is to establish a consistent terminology system by means of which these ESFD
configurations can be classified. It is anticipated that a companion testing standard using this classification system will
subsequently be developed.
A1.5 Basis of Classification
A1.5.1 An assembled ESFD and the bone(s) or bone analog(s) to which it is affixed constitute a fixator-bone construct.
A1.5.1.1 The assembled ESFD itself, apart from the host bone, is termed the fixator assembly.
A1.5.1.2 The individual parts (or modules of individual parts) from which the end user assembles the fixator are termed its
elements.
A1.5.2 An ESFD normally is configured to span a mechanical discontinuity in the host bone that otherwise would be unable to
transmit one or more components of the applied functional load successfully. This bony discontinuity is termed the mechanical
defect.
A1.5.3 Examples of mechanical defects are fracture surfaces, interfragmentary callus, segmental bone gaps, articular surfaces,
neoplasms, and osteotomies.
A1.5.4 Coordinate System(s)—The relative positions of the bones or bone segments bordering the mechanical defect should be
described in terms of an orthogonal axis coordinate system (Fig. A1.1).
A1.5.4.1 Where possible, coordinate axis directions should be aligned perpendicular to standard anatomical planes (for example,
transverse (horizontal or axial), coronal (frontal), and sagittal (median)).
A1.5.4.2 Where possible, translation directions should be consistent with standard clinical conventions (for example, ventral
(anterior), dorsal (posterior), cranial (cephalad or superior), caudal (inferior), lateral, or medial).
A1.5.4.3 Rotation measurement conventions must follow the right-hand rule and, where possible, should be consistent with
standard clinical terminology (for example, right or left lateral bending, flexion, extension, and torsion).
A1.5.5 A base coordinate system (X,Y,Z) should be affixed to one of the bones or major bone segments bordering the mechanical
defect. This bone or bone segment is termed the base segment, S , and serves as a datum with respect to which pertinent motion(s)
b
of bone segments or fixator elements, or both, can be referenced. Depending on context, S may be defined as being on either the
b
proximal or the distal side of a mechanical defect.
A1.5.6 The other bone(s) or bone segment(s) bordering the mechanical defect, whose potential motion(s) with respect to S is of
b
interest, is termed the mobile segment(s), S . If necessary, a local right-handed orthogonal coordinate system (x,y,z) may be
m
embedded within the S (s).
m
A1.5.7 Degrees of Freedom: Describing the position, or change in position, of S relative to S requires specifying one or more
m b
independent variables. These variables shall be termed positional degrees of freedom (P-DOF).
A1.5.7.1 Depending on context, this may involve as many as six variables (three translation and three orientation).
A1.5.7.2 Also depending on context, P-DOFs may be used to describe motions of interest in various magnitude ranges. For
example, P-DOFs may be used to describe one or more components of visually imperceptible motion (for example, elastic flexure
of a thick rod) or one or more components of grossly evident motion (such as interfragmentary motion at an unstable fracture site).
F1541 − 17
S = base segment
b
S = mobile segment
m
D = mechanical defect
O = origin of base reference frame
X, Y, and Z = base reference frame axes
o = origin of mobile reference frame
x, y, and z = mobile reference frame axes
R = transverse rod
t
R = longitudinal rod
L
P = pin
C = rod-rod connector
rr
C = pin-rod connector
pr
FIG. A1.1 External Fixator Definition Schematic
A1.5.8 Application or adjustment of an ESFD normally includes an attempt to achieve or maintain a specific position of S
m
relative to S . The adjustability afforded by the ESFD design for this purpose, most commonly, fracture fragment reduction, will
b
be characterized in terms of adjustment degrees of freedom (A-DOF).
A1.5.9 Some ESFDs are designed optionally to transmit selected components of loading or displacement across the defect, usually
by disengaging a locking mechanism. The component of motion of S permitted by such unlocking, often given the clinical name
m
“dynamization,” will be termed unlocked degrees of freedom (U-DOF).
A1.5.9.1 Depending on the specifics of design, the motion permitted in an unlocked degree of freedom may be opposed
substantially and deliberately by a specific mechanism such as a spring or a cushion. Such an unlocked degree of freedom is termed
a resisted unlocked degree of freedom.
A1.5.9.2 Unlocked degrees of freedom in which motion is induced actively by external energy input from devices associated with
the fixator are termed actuated degrees of freedom.
A1.5.9.3 An unlocked degree of freedom in which motion is unopposed by a specific design mechanism is termed an unresisted
unlocked degree of freedom. Incidental friction in a dynamizing element shall not be construed as representing deliberately resisted
F1541 − 17
motion; however, conditions involving untoward resistance to motion, for example, substantial binding friction, in a supposedly
unresisted degree of freedom should be identified.
A1.5.10 For adjustment or unlocked DOFs, the extrema of angular or translational displacement between which motion is
permitted before encountering a fixed or adjustable constraint are termed that DOF’s range of motion (ROM).
A1.5.11 A fixator assembly consists of a structurally purposeful arrangement of three basic types of elements: bone anchorage
elements, usually transcutaneous; bridge elements, usually extracutaneous; and connection elements.
A1.5.12 Anchorage elements are those that attach directly to the bone. Examples are smooth pins, threaded pins, screws, wires,
or cortex clamps.
A1.5.13 Bridge elements are structural members designed to transmit loads over relatively long distances, and they are joined to
one another or to anchorage elements, or both, by connectors. Bridge elements can either be simple or complex and should be
described in terms of their characteristic shape and, where appropriate, their orientation with respect to the bone or the mechanical
defect.
A1.5.13.1 Examples of simple bridge elements are longitudinal rods, transverse rods, rings, or ring segments. Simple bridge
elements need not be single-piece. If multipiece, however, the individual parts are joined rigidly rather than adjustable by the end
user.
A1.5.13.2 Complex bridge elements are mechanisms that consist of two or more subelements designed to function together to
achieve a specific kinematic objective. Examples of complex bridge elements are articulated or telescoping mechanisms.
A1.5.14 Connectors join bridge elements either to other bridge elements or to anchorage elements. Of the two elements
comprising any joint or junction, the connector is that element to which the end user applies an active gripping force or torque to
engage the attachment. Connectors should be described in terms of the types of elements that they connect and, where appropriate,
in terms of their adjustment or unlocked degrees of freedom. Examples of connectors are pin(-rod) clamps, pin cluster(-rod)
clamps, ring-rod clamps, and rod-rod clamps.
A1.5.15 That portion of the fixator assembly specifically excluding the bony anchorage elements and their associated connectors
is termed the frame. Connectors that join only bridge elements, or that join bridge elements to bone anchors but are not user
removable from bridge elements, are considered to be part of the frame.
A1.5.16 A joint or junction for which the relative positions between any two elements or subelements can be controlled by the
end user is termed an articulation. The components of relative motion permitted between the fixator elements at an articulation
should be described in terms of that articulation’s degrees of freedom, either A-DOF or U-DOF, depending on context.
Additionally, articulations should be described in terms of the types of elements that they connect.
A1.5.17 Joints at which the relative positions of the elements connected are fixed and cannot be controlled by the end user are
termed nonadjustable. Nonadjustable joints should be described in terms of the types of elements that they connect.
A1.6 Attributes
A1.6.1 Coupling between the assembled frame and the host bone is achieved by anchorage elements such as wires, pins (threaded
or unthreaded), screws, or cortex clamps (sometimes called claws or prongs). In long bone applications, anchorage elements
normally transmit load transversely from the host bone segments to the frame structure.
A1.6.1.1 Wires are thin, smooth, constant cross-section (usually circular) anchorage elements that transmit load from the host bone
to the frame primarily by axial tension as a result of transverse (“bow string”) distention by the host bone; therefore, wires must
transfix the bone and must be clamped to the frame at two sites. The stiffness of bone-frame coupling achieved using a wire
depends sensitively on the tension in the wire, which normally is controlled by the end user. Stoppers (“olives”) sometimes are
used to oppose incidental slippage along the length of a transfixing wire.
A1.6.1.2 Pins are slender anchorage elements, again, usually of circular cross section or envelope, for which bone-to-frame load
transmission occurs primarily by longitudinal bending stresses. Pins can penetrate one or (usually) both cortices of a long bone,
F1541 − 17
and they can be clamped to the frame at one end (“half-pins”) or both ends (“through-and-through pins” or “full-pins”). Pins can
either be smooth or threaded. Threaded pins can be designed for achieving purchase in cortical bone, cancellous bone, or in a
combination of the two. Pins can either be of constant cross section, shouldered, or tapered. They can be clamped to the frame
either individually or in clusters. Depending on the flute or thread design, or both, pins can be classified as being one of the
following:
(1) Self-drilling/self-tapping,
(2) Self-tapping/nonself-drilling, or
(3) Nonself-tapping/nonself-drilling.
A1.6.1.3 Screws are threaded anchorage elements, loaded primarily in axial tension or in transverse shear, or both. This term is
sometimes (mis)used interchangeably as a descriptor for ESFD threaded pins, but it is reserved more properly for devices that have
a head with a recess for wrenching (see Specification F543 and Reference Chart F544) and that are used to develop compression
across a fracture site or across a bone/implant interface.
A1.6.1.4 Cortex clamps (claws/prongs) are anchors that grip the host bone externally at two or more sites, without penetrating
through the full cortical thickness. Cortex clamps may or may not pierce the periosteum.
A1.6.2 Frame bridge elements are structural members configured in such a manner as to transmit functional load from the
anchorage elements on one side of the mechanical defect to those on the other side of the defect. Bridge elements can be simple
members such as smooth prismatic rods, threaded rods, bars, flat plates, curved plates, or arched plates. Alternatively, they can be
complex assemblies of several members, designed to allow or induce specific motions such as fixed axis rotation, linear sliding,
or active adjunct distraction. Most ESFD frames using simple bridge elements involve structural arrangements in which several
simple bridge elements are linked to one another by connectors.
A1.6.3 Fixator-Bone Construct Classifications—Constructs may be classified in accordance with the anatomic skeletal structure
to which the frame is applied. Common types are as follows:
A1.6.3.1 Long bone,
A1.6.3.2 Articular joint,
A1.6.3.3 Pelvis,
A1.6.3.4 Spinal, and
A1.6.3.5 Halo (skull).
A1.6.3.6 A construct subunit is one bony fragment plus its pins/wires and connectors and plus bridge elements not shared with
other bony fragments.
A1.6.4 Long bone frames or frame subunits can be characterized in terms of limb access.
A1.6.4.1 Frames or frame subunits that encompass 90° or less of an extremity sector circumferentially are termed unilateral.
A1.6.4.2 Frames or frame subunits that encompass more than 90° of an extremity sector circumferentially are termed multilateral.
Multilateral frames are often described in terms of their characteristic geometry: bilateral (two columns of longitudinal bridge
elements), triangular (three longitudinal columns), quadrilateral (four columns), or circular (ring fixators).
A1.6.5 Long bone frames or frame subunits (unilateral or multilateral) can be classified according to pin configuration, as follows:
A1.6.5.1 As one plane if all of their pins lie approximately within a common plane,
A1.6.5.2 Or as multiplane if their pins lie in two or more distinct planes.
A1.6.6 Constructs may be classified in terms of the means by which the frame is coupled to the bone.
F1541 − 17
A1.6.6.1 A frame for which coupling to the bone is by a homogeneous group of primarily moment-transmitting anchors such as
pins, screws, or cortex claws is termed a pin-fixed construct.
A1.6.6.2 If the coupling is by primarily tension-transmitting members instead, the construct is said to be wire fixed. The wire-fixed
constructs involve ring-type bridge elements in almost all instances.
A1.6.6.3 If coupling involves a heterogeneous mixture of wires and pins (or screws or other anchorage elements, or both), the
construct is said to incorporate hybrid coupling.
A1.6.7 Fixator constructs may be classified according to the degree of homology or similarity between the respective subunits.
A1.6.7.1 If the bone fragments on opposing sides of a mechanical defect are part of analogously assembled construct subunits,
the overall fixator is said to be symmetrically configured. This does not imply strict geometric symmetry about the defect mid plane,
but rather that each major element in each construct subunit possesses a similar counterpart in the other construct subunit.
A1.6.7.2 A construct whose subunits do not have such counterpart elements is said to have a hybrid, or asymmetrically configured,
frame.
A1.6.8 Some pin-fixed constructs allow independent control of each pin’s orientation and DOF of articulation with the frame. In
other designs, multipin clamps are used to control the common orientation and DOF of frame articulation of a small group of pins
termed a pin cluster. Pin cluster clamps most commonly enforce parallel alignment of the pins in the cluster. The specific A-DOF
and U-DOF of pin/frame articulation in each instance, that is, either independent or clustered pins, depends on the design of the
specific connecting element joining the pin(s) to the frame.
A1.6.9 Ring fixators have complex frames assembled from several transverse-plane ring or partial-ring bridge elements. The
anchoring transfixation tensile wires are connected to the rings individually. Longitudinal rods normally are used to connect the
transverse-plane rings.
A2. TEST METHOD FOR EXTERNAL SKELETAL FIXATOR CONNECTORS
A2.1. Scope
A2.1.1 This test method covers the procedures for determining the stiffness and strength of connecting elements (clamps) of
external skeletal fixators under axial loads and bending moments. Depending on the design of the connector and its use in the
overall construct, the connector needs to transmit one or more components of loading (tension, compression, torsion, or bending,
or a combination thereof) between the elements it grips (anchorage elements or bridge elements), without itself undergoing either
permanent deformation or excessive elastic deformation.
A2.1.2 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.
A2.1.3 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.
A2.2. Referenced Documents
A2.2.1 ASTM Standards:
E4 Practices for Force Verification of Testing Machines
F1541 − 17
A2.3. Terminology
A2.3.1 Definitions of Terms Specific to This Standard:
A2.3.1.1 connectors—external fixator elements used to join bridge elements either to other bridge elements, or to anchorage
elements.
(1) Of the two elements comprising any joint or junction, the connector is that element to which the end user applies an active
gripping force or torque to engage the attachment.
(2) Connectors should be described in terms of the types of elements, which they connect, and where appropriate, in terms of
their adjustment or unlocked degrees of freedom.
(3) Examples of connectors are pin(-rod) clamps, pin cluster(-rod) clamps, ring-rod clamps, and rod-rod clamps.
A2.3.1.2 input-loading axis—the line of application in the case of a force input, or the axis about which a moment is applied in
the case of a moment input.
A2.3.1.3 input-loading platen—a member, not normally part of the connector during clinical usage, through which the input force,
or moment, is delivered from the testing machine actuator to the connector.
A2.3.1.4 support platen—a member, also not normally part of the connector during clinical usage, through which the connector
is rigidly affixed to the testing machine base.
A2.4. Summary of Test Method
A2.4.1 Connecting elements (clamps) are obtained, and if applicable, assembled using the techniques and equipment
recommended by the manufacturer. Platens substituting for the body, or anchorage elements, or both, are attached to the connector
in such a manner that no slippage can occur relative to the connector. Axial loads or bending moments are applied to the connector,
and a graphical plot of load (or moment) versus displacement is used to determine the intrinsic stiffness, and strength, if tested to
failure, of the connector.
A2.5. Significance and Use
A2.5.1 These laboratory benchtop tests are used to determine values for the intrinsic stiffness, or strength, or both, of connectors,
under force or moment loadings. Since different connectors have different materials and geometries, stresses within individual
subcomponents or at subcomponent interfaces may differ substantially between designs. During testing, the connectors are loaded
and supported in such a manner that all measured deformation occurs within the connector itself, rather than at the interface
between the connector and the fixator element(s) gripped.
A2.5.2 The results obtained in this test method are not intended to predict the clinical efficacy or safety of the tested elements.
This test method is intended only to measure the uniformity of the elements tested or to compare the mechanical performance of
different connectors; however, the actual load that can be transmitted to the connector in clinical practice depends very much on
the slippage resistance of the different subcomponent interfaces.
A2.5.3 This test method may not be appropriate for all types of external skeletal fixator applications. The user is cautioned to
consider the appropriateness of the method in view of the materials and designs being tested and their potential application.
A2.6. Apparatus
A2.6.1 Force or Moment or both Application Fixture:
A2.6.1.1 The loading configuration is shown schematically in Fig. A2.1. The input loading axis must pass through one of the
platens (the loading platen) rigidly affixed to the connector. The other platen (the support platen) is rigidly affixed to the base of
the testing apparatus.
A2.6.2 Load Frame—Machines used for testing shall conform to the requirements of Practices E4. The loads used for this test
method shall be within the loading range of the test machine as defined in Practices E4.
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A = local coordinate system, defined with respect to land-
mark Point O
B = rod (as normally gripped by connector)
C = connector body
D = connector tightening mechanism(s)
E = rod grip platen (support platen)
G = rod grip interface
H = pins (as normally gripped by connector)
J = pin grip/clamp platen (loading input platen, rigidly
bonded to pin grip)
K = pin clamping interface
L = pin grip/clamp tightening mechanism
M = testing machine base (fixed)
N = pin grip/clamp (in this illustration, the input loading is a
force Fz* in the z* direction, delivered through a loading
platen rigidly affixed to the pin grip/clamp. δ is the dis-
z
placement of the loading platen in the z direction
FIG. A2.1 Schematic for Testing an External Fixator Connector (Example, Generic for a Pin-Rod Joint)
A2.6.3 Data Acquisition Device—A suitable recorder to plot a graph of load versus load frame displacement on perpendicular
axes. Optionally, this device may include the use of computer-based digital sampling and output of the load and displacement
signals.
A2.7. Test Specimen
A2.7.1 All tested connectors should be representative of clinical quality products.
A2.7.2 If the connector(s) to be tested have been used previously, the nature of such prior usage should be described appropriately.
A2.7.3 The test specimens should be prepared in the manner in which they would normally be used clinically. For example, if a
particular connector would normally be sterilized in a particular manner before clinical use, it should be similarly sterilized before
mechanical testing.
A2.7.4 If the connector to be tested is a prototype, or under development, or both, the geometric and material information needed
to characterize the component fully should either be included in the report, or detailed descriptive information should be
referenced.
F1541 − 17
A2.8. Procedure
A2.8.1 Configuring the Connecting Element for Testing:
A2.8.1.1 With the connecting element assembled in the configuration normally used, input and support platens are affixed in a
manner that insures that all measured deformations are intrinsic to the connecting element itself and are not influenced by possible
interfacial slippage between the connecting element and the fixator elements (for example, rods or anchorage pins) which it clamps.
(1) The input and support platens should made of steel or other metal and should have negligible compliance relative to that
of the connecting element itself.
(2) The input and support platens should have recesses to accommodate those fixator elements geometrically, for example,
anchorage pins or rods, normally clamped by the connecting element being tested.
(3) The input and support platens should be rigidly affixed to the connecting element (for example, by welding, epoxy,
cyanoacrylate cement, or other appropriate means).
A2.8.1.2 The input and support platens serve as attachments for gripping by the testing apparatus. This test method is applicable
only to those components of loading (force or moment, or both), which can be applied through such platens.
A2.8.1.3 A local right-handed coordinate system (X*,Y*,Z*) should be defined with respect to a specific origin landmark point on
(or in) the connecting element. The platen locations (position and orientation) should be identified relative to these local coordinate
axes.
A2.8.2 Mounting the Test Connector:
A2.8.2.1 The platen through which the input force (or moment) is to be applied is gripped, appropriately aligned, in the testing
machine. The support platen is rigidly affixed to the testing machine base.
A2.8.2.2 The grips and the testing machine itself should be sufficiently stiff that their deformation under load is negligible relative
to that of the connecting element being tested. The tare compliance of the testing machine and grips, that is, without the connector
mounted, should be measured and reported. Typically, the tare compliance of the testing machine plus grips should be less than
1 % of the compliance of the connector being tested. The gripping mechanism should be clearly described.
A2.8.3 Forces should be delivered through an input platen, which is rigidly bonded to the connector. Normally, the axis of loading
will be referenced to that of a member, such as a rod or a pin, that would be clamped by the connector. The line of action of the
input force should be recorded relative to the local coordinate system. Appropriate fixturing detail should be provided as to how
that force is applied through the input platen.
A2.8.4 Moments may be delivered either by an eccentrically applied force, or alternatively, by a torsional actuator. In the former
instance, the offset from the local coordinate system origin should be recorded. In either instance, the orientation of the moment
axis should be recorded relative to the local coordinate system. Appropriate fixturing details as to how that moment is applied
through the input platen should be provided.
A2.8.5 For connectors made entirely of metal or other materials exhibiting elastic behavior, the load (or moment) may be applied
quasistatically. An input rate sufficient to attain in 30-s force, or moment, magnitude in the range of typical clinical usage, or of
connector failure, shall be deemed quasistatic. For connectors incorporating polymeric or other materials that exhibit viscoelastic
behavior, load/stroke rates, which are in the range of those expected clinically, may instead be desirable. In either case, the rate(s)
used and a rationale for its choice should be provided.
A2.8.6 Tests may be run under either load or displacement control. They may either be single- or multi-cycle, and can be either
restricted to the elastic regime, or taken to failure of the connector. The specific conditions used should be described fully.
A2.8.7 If single-cycle testing is to be performed, the specimen shall be subjected to several preconditioning load cycles to
demonstrate that the reported load/deformation curve is repeatable from cycle to cycle.
A2.8.7.1 Preconditioning should be continued until the apparent stiffness of the connector changes less than 5 % between
subsequent cycles.
F1541 − 17
A2.8.7.2 Normally, about five preconditioning load cycles are suitable for this purpose, with peak applied load within the elastic
range, approximately 50 % of the expected physiologic service load or 50 % of the expected connector failure load, whichever is
lower.
A2.8.7.3 Load/deformation curves for the preconditioning cycles should be recorded. Preconditioning cycle stiffnesses should be
reported.
A2.8.8 Data Recording—The load (N) or torque (N-m) and linear (mm) or angular (°) displacement measured by the testing
machine should be continuously recorded. The linear displacement should be measured at the point of load application. In some
instances it may be appropriate also to record components of deformation in directions other than that of the applied loading. If
so, the sensors used, for example, dial gages or linear variable differential transducers (LVDTs), and the points and directions of
their measured deformations should be recorded.
A2.9. Calculation or Interpretation of Results
A2.9.1 Stiffness (units according to the chosen load and deflection configuration, for example, N/mm for force, N-mm/degree for
moment) shall be calculated from the slope of the linear-most portion of the load/deflection curve, as apparent visually (Fig. A2.2,
Point A). If an objective slope determination technique, for example, curve fitting of a digitized tracing, is used, this should be
described. The load and deflection configuration (location of measuring element and direction of the measured vector) shall be
defined clearly with respect to the loading axis of the testing equipment (Fig. A2.1).
A2.9.2 Failure load (N or N-mm) of the connector is frequently associated with a discontinuity in the load/deformation curve.
Depending on context, additional load uptake may or may not be possible after occurrence of this discontinuity. In the former
circumstance (Fig. A2.2, Point B), the severity of the discontinuity should be measured in terms of change in slopes of the
load/deformation curve for loads immediately below and above the discontinuity point. In the latter circumstance (Fig. A2.2, Point
C), the failure load should be designated as the ultimate strength of the connector.
A2.9.3 In situations in which there is no clear discontinuity in the load displacement curve, other definitions of failure load may
be used.
A2.9.3.1 For situations in which permanent deformation occurs, for example, as a result of interfacial slip or plastic deformation,
NOTE 1—Stiffness is defined as the slope of the linear-most portion of the curve, here evaluated by a tangent drawn at Point A. Point B illustrates a
slope discontinuity (possibly indicative of interfacial slip or subcomponent failure within the connector), and Point C illustrates the maximal load
acceptance (ultimate strength).
FIG. A2.2 Load/Deformation Curve (Generic, Here Illustrated for the z* Direction)
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or both, within the connector, an offset criterion may be used. In this instance, the failure load is defined as that load necessary
to induce a specific amount of permanent deformation, either linear or angular, depending upon the degree of freedom being tested,
upon release of the applied load.
A2.9.3.2 For situations in which excessive elastic deformation occurs within the connector, failure may be defined in terms of a
specific fractional reduction of the connector’s small-load stiffness. For example, failure might be defined in terms of the
connector’s tangent stiffness having fallen to 25 % of the tangent stiffness that was apparent at a load of 50 N.
A2.10. Report
A2.10.1 The test report shall include, but is not limited to, the following information:
A2.10.1.1 Connecting Element Identification, including manufacturer, part number, nomenclature, and quality control or lot
number. If the part is a prototype, geometrical and material descriptions shall be included.
A2.10.1.2 Specimen preparation condition, for example, sterilization and description of prior usage history, if applicable.
A2.10.1.3 Connecting force or torque used to engage the connector’s gripping mechanism.
A2.10.1.4 Configuration of the (bonded) platens and testing apparatus grips.
A2.10.1.5 Specific degrees of freedom tested, such as, tension or compression, torsion, or bending. In each case, the axis along
which or about which loading is applied should be specified.
A2.10.1.6 Loading rate and number of cycles (fatigue tests).
A2.10.1.7 Stiffness, and, if loaded to failure, the failure criterion and strength, in the specific direction(s) tested.
A2.10.1.8 In cases in which the mode of failure is ascertainable, for example, visually apparent interfacial slippage of a specific
subcomponent interface, the nature of such failure should be described.
A2.11. Precision and Bias
A2.11.1 Data establishing the precision and bias to be expected from this test method have not yet been obtained.
A2.12. Keywords
A2.12.1 bending moments; connecting elements; connectors; external fixator; orthopedic device; stiffness; strength
A2.13 Rationale
A2.13.1
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