ISO 16087:2013

Implants for surgery - Roentgen stereophotogrammetric analysis for the assessment of migration of orthopaedic implants

ISO 16087:2013 provides requirements for the clinical assessment of migration of orthopaedic implants with roentgen stereophotogrammetric analysis (RSA).

Implants chirurgicaux — Analyse stéréophotogrammétrique Roentgen pour l'évaluation de la migration des implants orthopédiques

General Information

• Status: Published
• Publication Date: 30-Sep-2013
• ICS: 11.040.40 - Implants for surgery, prosthetics and orthotics
• Technical Committee: ISO/TC 150/SC 4 - Bone and joint replacements
• Drafting Committee: ISO/TC 150/SC 4 - Bone and joint replacements
• Current Stage: 9093 - International Standard confirmed
• Start Date: 27-Jan-2025
• Completion Date: 13-Dec-2025

Overview

ISO 16087:2013 - "Implants for surgery - Roentgen stereophotogrammetric analysis for the assessment of migration of orthopaedic implants" defines requirements for using Roentgen stereophotogrammetric analysis (RSA) to measure three‑dimensional migration between orthopaedic implants and host bone. The standard covers terminology, measurement methodology, radiographic setup, calibration, software and coordinate systems, validation (accuracy and precision), and standardized output for clinical RSA studies. CAUTION: RSA uses X‑rays and increases patient radiation exposure; clinical benefit versus risk should be considered.

Key topics and technical requirements

• Markers and virtual markers: Use of small spherical, biocompatible, radio‑opaque markers (e.g., tantalum). Common marker diameters: 0.5 mm, 0.8 mm, 1.0 mm. Virtual markers (defined in the images) can be used to compare specific implant points across studies; a crossing‑line error < 1 mm is advised.
• Calibration objects: Use of calibration cages or reference plates to define the global 3‑D coordinate system and to determine X‑ray focus positions.
• Radiographic arrangement: Specifies biplanar (angled) and uniplanar setups, radiograph quality, and recommendations for double examinations (repeat imaging within minutes) to assess precision.
• Coordinate systems and modelling: Definitions for global and implant coordinate systems, reference rigid body, and model‑based RSA methods where 3‑D implant models are matched to radiographic projections.
• Measurement metrics: Definitions and requirements for reporting migration, translations, rotations, maximum total point motion (MTPM), mean error of rigid body fitting, condition number (marker distribution quality), accuracy and precision validation.
• Software and validation: Requirements for RSA analysis software and procedures to validate accuracy and precision; Annex A provides relevant formulae.
• Practical considerations: Addresses weight bearing, follow‑up intervals, radiation dose management, and criteria for excluding patients.

Applications and users

ISO 16087:2013 is intended for:

• Orthopaedic researchers conducting clinical trials on joint replacements and implant fixation
• Clinicians and radiologists performing RSA follow‑up studies to predict long‑term implant survival
• Medical device manufacturers and regulatory bodies using RSA as a sensitive surrogate outcome measure in early device screening
• Imaging centres and software developers implementing RSA workflows and analysis tools

RSA is particularly valuable for early clinical evaluation of implant migration because of its high accuracy, enabling smaller sample sizes in comparative studies.

Related standards

• Standards and guidance on implants for surgery and medical imaging (ISO/TC 150 work) are complementary to ISO 16087:2013. Users should also consult applicable device‑specific and radiation safety standards and local regulatory guidance when implementing RSA.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 16087
First edition
2013-10-01
Implants for surgery — Roentgen
stereophotogrammetric analysis
for the assessment of migration of
orthopaedic implants
Implants chirurgicaux — Analyse stéréophotogrammétrique
Roentgen pour l’évaluation de la migration des implants
orthopédiques
Reference number
©
ISO 2013
© ISO 2013
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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the requester.
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Published in Switzerland
ii © ISO 2013 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
3 Measurement . 3
3.1 Size of markers . 3
3.2 Virtual markers . 3
3.3 Number and distribution of markers . 4
3.4 Mean error of rigid body fitting . 4
3.5 Condition number . 4
3.6 Three-dimensional implant models . 4
4 Radiographic arrangement . 4
5 Calibration cages and reference plates . 4
6 Radiographs . 5
6.1 General . 5
6.2 Double examinations . 5
7 Software . 5
8 Coordinate systems . 5
8.1 Global coordinate system . 5
8.2 Implant coordinate system . 5
8.3 Reference rigid body . 6
9 Migration . 6
9.1 Translations . 6
9.2 Rotations . 6
10 Maximum total point motion . 7
10.1 General . 7
10.2 Signed versus unsigned values. 8
11 Validation . 8
11.1 Accuracy . 8
11.2 Precision . 8
12 Practical issues . 8
12.1 Weight bearing . 8
12.2 Follow-up intervals . 9
12.3 Radiation dose . 9
12.4 Exclusion of patients . 9
13 Standardised output . 9
Annex A (informative) Relevant formulae .11
Bibliography .12
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
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
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 documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2. www.iso.org/directives
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received. www.iso.org/patents
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
The committee responsible for this document is ISO/TC 150, Implants for surgery, Subcommittee SC 4,
Bone and joint replacement.
iv © ISO 2013 – All rights reserved

Introduction
[1]
Since its introduction in 1974, roentgen stereophotogrammetric analysis (RSA) has been widely
used to assess migration of orthopaedic implants. It is a highly accurate method of quantifying
three-dimensional migration between an implant and the bone it is fixed in. RSA is also used in other
applications such as measuring migration between bone fragments in e.g. bone fracture studies, and
measuring wear of implants. These applications are not within the scope of this International Standard.
Several studies have found implant migration to be predictive of long-term implant survival and, for
most devices, measurement over two years might therefore provide a surrogate outcome measure with
[2][3]
relatively low numbers of subjects, e.g. less than 50 patients in each group in randomized studies.
[4]
A smaller number of subjects can be used in these studies as a consequence of the high accuracy of
the measurement technique. Because of this, RSA is an important technique in early clinical trials for
screening new joint replacement prostheses.
However, results from these early clinical trials are difficult to compare as different studies report
their results in different formats. To facilitate comparison of outcome reported from different research
groups and because the results are obtained using different methodological procedures, there is a need
for standardization of RSA investigations.
The RSA method described in this International Standard requires the use of X-rays and exposes the
patient to a greater X-ray exposure dose with its associated health risk. For this reason, it is neither
the intention of this International Standard to recommend the routine use of RSA nor to add to existing
regulatory requirements. Rather it is the intention that when RSA is used in a standardized manner, the
results can be as useful and as widely applicable as possible.
INTERNATIONAL STANDARD ISO 16087:2013(E)
Implants for surgery — Roentgen
stereophotogrammetric analysis for the assessment of
migration of orthopaedic implants
CAUTION — The RSA method described in this International Standard requires the use of X-rays
and exposes the patient to a greater X-ray exposure dose with its associated health risk. Careful
consideration of the benefits and drawbacks of this method on a case by case basis is advisable.
1 Scope
This International Standard provides requirements for the clinical assessment of migration of
orthopaedic implants with roentgen stereophotogrammetric analysis (RSA).
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
absolute movement
movement of a rigid body relative to a fixed reference rigid body
2.2
accuracy
closeness of agreement between a measured quantity value and a true quantity value of a measurand
2.3
bias
estimate of a systematic measurement error
2.4
biplanar technique
RSA technique where two X-ray cassettes/films/sensors are set at an angle to each other
2.5
calibration cage
calibration box
reference frame used to create a three-dimensional coordinate system, with definition of position and
orientation, and to determine the position of the two roentgen foci
2.6
condition number
calculated number used to assess the distribution of markers
Note 1 to entry: High condition numbers indicate poor marker distribution, while low condition numbers indicate
appropriate marker distribution.
Note 2 to entry: See Annex A, which establishes the methodology to determine the condition number associated
with the marker distribution.
2.7
crossing line error
shortest distance between the two X-rays projecting the centre of a marker in the two RSA images
2.8
double examinations
two RSA examinations of the same patient within an interval of several minutes
2.9
helical axis
screw axis
instantaneous axis about which the decomposition of the motion of an object from one position to
another has a translation along and a rotation about a single axis
2.10
marker
small diameter biocompatible metal sphere having a precise size and shape used as landmark
Note 1 to entry: Spherical tantalum markers serve as well-defined landmarks.
Note 2 to entry: The diameter is commonly ≤ 1 mm.
2.11
maximum total point motion
MTPM
length of the translation vector of the marker or virtual marker in a rigid body that has the greatest migration
Note 1 to entry: It can only have positive values, and is not normally distributed.
2.12
mean error of rigid body fitting
rigid body error
measure indicating the mean change of relative positions of markers (in the same object) over time
compared to the initial, reference configuration
Note 1 to entry: Annex A establishes the methodology to determine the mean error associated with the change of
relative positions of markers.
2.13
migration
change in position and orientation of an implant relative to the host bone assessed between follow-
up examinations
2.14
model-based RSA
RSA technique in which the position and orientation of an implant is assessed by matching a virtual
projection of a three-dimensional model of the implant to the actual radiographic projection of the implant
2.15
phantom
object that is used as a representative of an anatomical part
2.16
precision
degree to which repeated measurements under unchanged conditions show the same results
2.17
reference plate
planar object holding markers used for calibration of RSA-examinations by linking its two-dimensional
coordinate system to the three-dimensional global coordinate system of previous RSA-examinations
that were calibrated using a three-dimensional calibration cage
2.18
reference rigid body
rigid body that defines a fixed coordinate system, the origin of which is located in that rigid body’s
geometrical centre
2 © ISO 2013 – All rights reserved

2.19
rotation matrix
mathematical expression of the three-dimensional rotation of a rigid body
2.20
RSA
roentgen stereophotogrammetric analysis
radiostereometry
radiostereometric analysis
roentgen stereophotogrammetry
measurement technique that relies on stereo X-ray images and can be used to assess relative changes in
position and orientation of two rigid bodies (e.g. an orthopaedic implant and host bone) relative to each other
Note 1 to entry: In order to reach a high level of accuracy, markers are used as landmarks in the bone and a
calibration object (calibration cage or reference plate) is used to assess the position of two synchronised X-ray
sources in the global coordinate system defined by the calibration cage.
2.21
virtual marker
three-dimensional point from visible landmarks or calculated from known geometry to determine a
specific point of an implant
Note 1 to entry: Virtual markers were formerly named fictive markers.
2.22
uniplanar technique
RSA technique where the two X-ray cassettes/films/sensors are in the same plane
3 Measurement
3.1 Size of markers
Spherical markers made of biocompatible (implant grade) metal and having a high radio-opacity (e.g.
tantalum) shall be used to serve as landmarks. Marker diameters of 0,5 mm, 0,8 mm and 1,0 mm are
generally used.
3.2 Virtual markers
Virtual markers indicate a specific part of the implant and facilitate comparison of migration data within
and between studies.
EXAMPLE 1 Within a clinical RSA study of a specific implant, these virtual markers are valuable if one or more
implant markers of a certain patient are obscured in the X-ray or have become loose.
In different RSA studies, different prosthesis designs might have markers attached at different locations.
In order to compare the translation of specific points on the implant’s surface between different implant
designs, virtual markers can be used.
EXAMPLE 2 To compare the translation of a specific point, on the tip of different hip stems.
A virtual marker is defined by the observer. Its position is indicated in both images of a single RSA-
examination, and the three-dimensional position of the virtual marker is reconstructed according to
the common approach of reconstructing the position of an actual prosthesis marker. It is advised that
the crossing line error is less than 1 mm. A new rigid body is formed when the position of the virtual
marker is combined with the positions of at least three prosthesis markers. This enables the translation
of the virtual marker to be determinable in subsequent (or previous) RSA examinations. Therefore,
virtual markers are defined such that they move with the implant and they can be used to calculate the
translation of this specific point of the prosthesis based on the migration of the implant itself.
3.3 Number and distribution of markers
In order to assess translations and rotations with all six degrees of freedom, markers shall be implanted
on each rigid body under study so that they are not collinear. For each rigid body, at least three identical
markers shall be visible on both radiographs at all examinations.
NOTE 1 In cases where only one or two markers can be used in one of the rigid bodies, only translations can
be calculated.
NOTE 2 It is strongly advised to insert at least six to seven bone markers as markers may be obscured by the
implant.
3.4 Mean error of rigid body fitting
The upper limit of acceptable mean error of rigid body fitting shall be related to the marker configuration
of the segment (defined by its condition number). The upper limit accepted shall be reported and should
typically not exceed 0,35 mm.
3.5 Condition number
For studies of hip, knee and shoulder prostheses, condition numbers shall be below 120.
For studies of small joints, such as in the fingers and the cervical spine, condition numbers shall
preferably be below 150. For studies in which these high condition numbers are accepted, it is essential
that the precision of the measurements is validated (see 11.2).
3.6
...