ISO 22926:2023

Implants for surgery — Specification and verification of synthetic anatomical bone models for testing

This document provides requirements and recommendations for specification and verification of synthetic anatomical bone models for use in testing of implants. The anatomical source of the synthetic model can be digital data from computed tomography (CT) scanning or any other sources such as from cadaveric specimens or statistically determined shape data. The specifications covered in this document are 3D shape and mechanical characteristics. Other characteristics, such as colour or cosmetic features, are not considered in this document.

Implants chirurgicaux — Spécification et vérification des modèles osseux anatomiques synthétiques pour les essais

Le présent document fournit des exigences et des recommandations pour la spécification et la vérification des modèles osseux anatomiques synthétiques pour une utilisation dans les essais d’implants. La source anatomique du modèle synthétique peut être les données numériques obtenues par tomodensitométrie, ou toute autre source telle que des échantillons cadavériques ou des données de forme déterminées statistiquement. Les spécifications abordées dans le présent document sont la forme 3D et les caractéristiques mécaniques. D’autres caractéristiques, telles que la couleur ou l’aspect esthétique, ne sont pas prises en compte dans le présent document.

General Information

• Status: Published
• Publication Date: 30-Jul-2023
• ICS: 11.040.40 - Implants for surgery, prosthetics and orthotics
• Technical Committee: ISO/TC 150 - Implants for surgery
• Drafting Committee: ISO/TC 150 - Implants for surgery
• Current Stage: 6060 - International Standard published
• Start Date: 31-Jul-2023
• Due Date: 15-Oct-2023
• Completion Date: 31-Jul-2023

Overview

ISO 22926:2023 - Implants for surgery: Specification and verification of synthetic anatomical bone models for testing defines requirements and recommendations for specifying, verifying and reporting synthetic anatomical bone models used in implant testing. The standard focuses on 3D shape and mechanical characteristics (not cosmetic features). Digital anatomical sources can include CT scans, cadaveric-derived data or statistically determined shape datasets that are used to produce physical synthetic models via casting, machining or additive manufacturing.

Key technical topics and requirements

• Scope and focus
  • Covers specification and verification of synthetic bone models for implant testing.
  • Excludes colour and cosmetic characteristics.
• Digital and physical models
  • Defines a digital anatomical bone model (STL, CAD/STEP, voxel models) and the resulting synthetic anatomical bone model.
• Required physical model characteristics
  • 3D overall shape and segmented anatomy (e.g., cortical, cancellous, intramedullary canal).
  • Material properties: density, hardness, porosity, Young’s modulus, surface roughness.
  • Structural mechanical characteristics: stiffness, ultimate strength, fatigue strength under specified loading.
  • Other relevant characteristics: thermal/chemical resistance, residual stress, dimensional stability, fluid absorption.
• Verification process
  • Three-step verification: model geometrical verification, model material verification, and model mechanical verification (when required).
  • Geometrical verification requires comparison to the digital model and consideration of measurement protocol, device and software errors (fiducial points, registration variability).
  • Material and mechanical verifications are compared to the specified properties and reported.
• Traceability and reporting
  • Producers must ensure traceability through design and manufacturing.
  • A specification report must document intended use, geometry, measurement methods and protocols, test results (mean, max, deviations), material tests and any limitations or contraindications. Annex C provides an example report; Annex B gives geometrical verification examples.

Practical applications

• Standardizes how synthetic bone models are specified and verified for:
  • Mechanical testing of orthopaedic implants and fixation constructs (stiffness, strength, fatigue).
  • Preclinical device development, bench testing and comparative performance studies.
  • Verification of manufacturing processes for medical device test fixtures and surgical tool validation.
• Helps users choose models with appropriate anatomical fidelity and mechanical behavior for their specific implant tests.

Who should use this standard

• Synthetic bone model producers and manufacturers
• Medical device developers and test engineers
• Biomechanics laboratories and notified bodies
• Regulatory and quality teams preparing test evidence for implants
• Research groups conducting implant or surgical tool evaluation

Related standards

• ISO 19213 - Test methods for synthetic cortical bone materials (referenced for material testing)
• ASTM F1839 - Specification for rigid polyurethane foam (material commonly used as cancellous bone analogue)

Keywords: ISO 22926, synthetic anatomical bone models, implant testing, 3D shape verification, model material verification, geometrical verification, specification report, CT-based bone models.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 22926
First edition
2023-07
Implants for surgery — Specification
and verification of synthetic
anatomical bone models for testing
Reference number
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
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or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Design and development of a synthetic model . 2
4.1 General . 2
4.2 Identification of physical model characteristics . 2
4.3 Model verification . 3
4.3.1 General . 3
4.3.2 Model geometrical verification . 3
4.3.3 Model material verification . 3
4.3.4 Model mechanical verification . 3
5 Specification report .4
Annex A (informative) Background, detailed scope and rationale . 5
Annex B (informative) Example of model geometrical verification methods .8
Annex C (informative) Example of a specification report .10
Bibliography .17
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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expressions related to conformity assessment, as well as information about ISO's adherence to
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 150, Implants for surgery.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Synthetic anatomical bone models can be useful to characterize mechanical performance of surgical
implants and instruments, such as those used in musculoskeletal fixation or reconstruction surgery. A
synthetic bone model is typically made by methods of casting, machining and/or recently by additive
manufacturing, all of which can leverage medical image-based modelling. To use a synthetic anatomical
bone model for mechanical testing of an implant, its similarity to natural bone in terms of shape and
mechanical behaviour is of paramount importance to bone model users.
This document provides a way to specify, verify and report characteristics of synthetic bone models
used for implant testing. The details of testing and the choice of a suitable bone model is outside the
scope of this document. A more detailed rationale for this document is provided in Annex A.
There are two related standards for synthetic materials that are used as mechanical models of bone
[1]
for implant testing. ASTM F1839 was first issued in 1997 and is a standard specification for rigid
polyurethane foam. Polyurethane foam is a cellular solid that exhibits certain aspects of mechanical
behaviour that are similar to bone such as the relationship between apparent density and its stress-
[2]
strain response to mechanical loading. A second relevant standard is ISO 19213 which was first
issued in 2017 and provides a list of test methods to describe synthetic material models of cortical bone.
The methods referenced in ISO 19213 report material properties from long standing test methods for
plastics, and include specialized tests to mimic certain orthopaedic surgical processes such as drilling,
milling (burring) and cutting. This document goes beyond materials, and includes shape and structure
of a synthetic bone model.
While the scope of this document is limited to bone models, it is intended to lay the framework for
future models of other biologic tissues.
v
INTERNATIONAL STANDARD ISO 22926:2023(E)
Implants for surgery — Specification and verification of
synthetic anatomical bone models for testing
1 Scope
This document provides requirements and recommendations for specification and verification of
synthetic anatomical bone models for use in testing of implants.
The anatomical source of the synthetic model can be digital data from computed tomography (CT)
scanning or any other sources such as from cadaveric specimens or statistically determined shape data.
The specifications covered in this document are 3D shape and mechanical characteristics. Other
characteristics, such as colour or cosmetic features, are not considered in this document.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
digital anatomical bone model
digital model
dataset to represent the shape and any other desired characteristics for target synthetic model (3.2)
Note 1 to entry: The procedure to produce digital model of the knee bone from computed tomography (CT) data
can be found in ISO 19233-1.
EXAMPLE STL, CAD STEP, voxel-based model.
Note 2 to entry: Examples of other desired characteristics are: density, hardness, porosity, Young’s modulus.
3.2
synthetic anatomical bone model
synthetic model
physical model resulting from the manufacturing process based on the digital model (3.1)
3.3
physical model characteristic
parameter or feature used to represent the physical anatomical bone in order to establish the design
requirements for the synthetic model (3.2)
Note 1 to entry: The physical model characteristics include both geometrical shape, material and mechanical
properties.
Note 2 to entry: Physical model characteristics can be specified by the bone model producer (3.4) and/or user.
3.4
bone model producer
model producer
organization or individual responsible for producing the synthetic model (3.2)
3.5
bone model user
model user
organization or individual that uses the synthetic model (3.2)
3.6
specification report
report which provides information of characteristics of the synthetic model (3.2) manufactured
according to the design requirements established in this document
Note 1 to entry: See Annex C for an example.
4 Design and development of a synthetic model
4.1 General
The applicable requirements for characterizing physical and digital anatomical bone models, and
verification after production are shown in 4.2 to 4.3.
The bone model producer shall establish appropriate system controls in order to ensure the traceability
of each synthetic anatomical bone model throughout the design and development process.
4.2 Identification of physical model characteristics
The required physical model characteristics shall be specified by either the bone model producer or the
bone model user. This specification shall include any of the following if required based on the intended
application of the model:
a) the overall shape described geometrically in any manner, such as surface model (e.g. an STL file),
solid vector model (e.g. CAD STEP file), or volumetric representation (e.g. voxel based model), as
input for an overall digital bone model;
b) the description of the 3D shapes of any segments within the overall shape [of list item a)], such as
cortical bone, cancellous bone and intramedullary canal;
c) the material and properties for the overall model or each segment, such as density, hardness,
porosity, surface roughness and Young’s modulus;
d) structural mechanical characteristics of the overall or part of the bone model, such as stiffness,
ultimate strength and fatigue strength, under certain loading conditions;
e) any other characteristics such as chemical or thermal resistance, residual stress levels and
dimensional stability due to manufacturing process, and fluid absorption in the intended working
environment of the model.
The bone model user should determine which of the above characteristics are critical for their
application and which verification model is needed.
NOTE Reference of material and mechanical characteristics for human bone segments can be collected from
the published literature, for examples, see References [3] to [11].
4.3 Model verification
4.3.1 General
To verify that the synthetic anatomical bone model fulfils the requirements of desired digital model,
this process shall be conducted by the bone model producer, and the results reported to the bone model
user. This verification includes model geometrical and model mechanical performance if required,
according to the following steps:
a) model geometrical verification (4.3.2),
b) model material verification (4.3.3), and
c) when necessary, model mechanical verification (4.3.4).
The bone model producer shall select and implement the processes for model geometrical, material and
mechanical verifications of the synthetic anatomical bone model as required or agreed with the bone
model users.
Results of verification shall be presented in specification report in accordance with Clause 5.
4.3.2 Model geometrical verification
Geometrical characteristics of the synthetic anatomical bone model shall be verified by examining the
agreement to the geometrical specifications established in 4.2 a) and b). Geometrical characteristics
are specified and referenced by the combination of
— anatomical landmarks, and
— digital anatomical bone model.
A detailed example of a model geometrical verification is provided in Annex B.
The results of the model geometrical verification shall be reported in accordance with Clause 5.
The interpretation of the agreement between the synthetic model and its reference shall also consider
effects and errors from the measurement protocol, the measurement device and the software used in
the protocol, including
— the choice of fiducial points including their location, and
— the variability of the results from registration and computation of the deviation between the
synthetic and the intended digital model.
When the protocol or instruments used for measurement of the digital anatomical and synthetic
anatomical bone models differ, such differences shall be reported.
4.3.3 Model material verification
Materials and other characteristics for each spatial segment or region of the synthetic anatomical bone
model shall be verified by comparison to the specifications established in 4.2 c). The results of the
model material verification shall be reported in accordance with Clause 5.
NOTE Testing methods of material characteristics can be found in various ISO and ASTM standards. For
cortical segment, the mechanical characteristics of the bone materials can be tested according to ISO 19213.
4.3.4 Model mechanical verification
Structural mechanical characteristics of the synthetic anatomical bone model shall be verified
by comparison to the specifications established in 4.2 c) or d). The results of the model mechanical
verification shall be reported in accordance with Clause 5.
5 Specification report
The specification report shall include at least the following information.
Provide reporting recommendations for model definition, creation, verification and use.
a) Intended use: The intended use of the synthetic anatomical bone model typically has, but is not
limited to the following:
— anatomical part that the model represents,
— population that the model assumes to reflect,
— if any anomaly that the model represents,
— expected implants that is used with the model,
— tests that are performed with the model, and
— if any contraindication or warning regarding reasonably foreseeable misuse of the model.
EXAMPLE Femur model for primary stiffness evaluation of fracture fixation constructs. Such
a model is typically used for stiffness testing of various fracture fixation constructs simulating
orthopaedic trauma treatments. The model here simulates a fractured or intact femur repair with one
or more trauma plates and screws, and the stiffness of the construct is tested in anterior-posterior
bending, medial-lateral bending, axial compression and/or torsion, or any combination of those.
b) Geometrical characteristics identified in 4.2 a) and b) and measurement methods to verify them.
Typical examples are:
— name or any identification information to specify the digital anatomical bone model,
— dimensions of anatomical landmarks, e.g. total length,
— for measurements to create the digital anatomical bone model, the measurement methods (e.g.
CT scan) and details of the protocol used,
— effects and errors from measurement protocol, measurement device and software used,
— error allowance of those specifications,
— result of measurements, either in absolute dimensions or relative bias or deviation from the
digital anatomical bone model. This may be written in the maximum, mean value, etc.,
— for characterization of the synthetic anatomical bone model, the measurement methods and
devices used, number of specimens (assume three when omitted), and how the resulting
measurements for different specimens are combined in data processing and interpreted, and
— any other measurement conditions that can affect the results of geometrical verification, e.g.
ambient temperature.
c) Material and other characteristics in 4.2 c), and testing methods.
d) If there are applicable mechanical characteristics, methods to verify them.
e) If any, other characteristics that can affect the results of testing using the model.
EXAMPLE Estimated lifetime, manufacturing process, storage conditions.
NOTE 1 See Annex C for an example.
NOTE 2 The contents of this specification report are only related to model geometrical, material and
mechanical verification. Other characteristics can be also included to inform to the bone model users.
Annex A
(informative)
Background, detailed scope and rationale
A.1 General
This document is intended to provide a way to specify, verify and report characteristics of synthetic
bone models used for implant testing. This document is useful for the model producer and model
users, because it defines the terms that are necessary to describe the synthetic models and provides a
suggested set of characteristics that can be useful in specifying the model. A specification report based
on this document will help both the producer and the user of a bone model to have structure and clarity
in what a bone model is, how it was tested, the results of the verification tests and how the models from
different producers can be more easily compared.
This document has been proposed as a response to the demands and progress of technology, including:
— increasing demands on in situ bench testing of implants for even greater patient safety;
— emerging technology of the digital transformation in production of both implants and bone models,
including digital data workflow, 3D images or digitizer, 3D CAD, numerical control machining and
additive manufacturing;
— potential of the patient specific implants.
Therefore, this document assumes that the workflow is centred around the digital model. However, this
document does not specifically assume bone models for patient specific implants or models produced
by the additive manufacturing. It is also applicable and useful for bone models not manufactured from
digital data such as casting, which is indeed the majority production method to date.
These new technologies made productio
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