ISO/TS 16955:2016

Prosthetics - Quantification of physical parameters of ankle foot devices and foot units

ISO/TS 16955:2016 describes quantitative methods to evaluate or assess key performance indicators of prosthetic ankle foot devices. For each method, the set-up and test configurations are described. Also included is a variety of parameters which are derived or calculated from the recorded data.

Prothèses — Quantification des paramètres physiques des dispositifs de cheville/pied et unités pour les pieds

General Information

• Status: Published
• Publication Date: 07-Jun-2016
• ICS: 11.040.40 - Implants for surgery, prosthetics and orthotics
• Technical Committee: ISO/TC 168 - Prosthetics and orthotics
• Drafting Committee: ISO/TC 168 - Prosthetics and orthotics
• Current Stage: 9092 - International Standard to be revised
• Start Date: 27-Sep-2022
• Completion Date: 13-Dec-2025

Overview

ISO/TS 16955:2016 is a Technical Specification from ISO/TC 168 that defines quantitative test methods to evaluate key performance indicators (KPIs) of prosthetic ankle–foot devices and foot units. It specifies test setups, sensor configurations and derived parameters (stiffness, lever arm, effective foot length, torsional and frontal-plane characteristics, energy, full-contact motion, etc.). The document describes how to record force, displacement, moment and angular data and how to calculate metrics that characterize device mechanical behaviour. Note: this TS defines measurement methods only; correlation of these metrics to user benefit is addressed separately.

Key topics and requirements

• Scope: methods to quantify mechanical performance of ankle–foot prostheses (jointed and unjointed with elastic elements).
• Mandatory quantification: to claim compliance all parameters in the TS must be measured and the strength requirements of ISO 22523:2006 must be met.
• Test setup: use coordinate system and configurations in ISO 22675:2016; tests are defined for a 26 cm foot sized for a 70 kg amputee.
• Sensor placement: a force–moment sensor positioned above midfoot at 500 mm height; displacement and angular sensors rigidly connected to record vertical displacement and torsional angle.
• Loading profiles and limits:
  • Heel/toe: sinusoidal load to 120 % of designed max body weight (example in TS: 824 N) with loading/unloading time (1 ± 0.1) s.
  • Mid-foot: peak load 200 % (1 373 N) with plate horizontal, same timing.
  • Roll-over tests apply force over plate angles −15° to +20° with duration 600 ms ± 10 %.
• Calculated parameters include: stiffness, lever arm length and change, effective foot length/width, full contact motion, torsional stiffness and angular range, and energy (integral of force × displacement).

Applications and users

ISO/TS 16955:2016 is practical for:

• Prosthetic manufacturers - product development, design validation and comparative performance testing.
• Test laboratories - standardized measurement protocols for R&D and QA.
• Clinical researchers - objective mechanical metrics to support studies linking device mechanics to gait outcomes.
• Regulators and procurement - consistent data for specification, acceptance testing and product comparison.

Using this TS helps produce repeatable, comparable mechanical data (stiffness, roll-over, torsion, frontal response) that support better device selection, optimization and communication of device characteristics.

Related standards

• ISO 22675:2016 - test configurations and coordinate system referenced by the TS.
• ISO 22523:2006 - strength requirements that must be met.
• ISO 10328 - structural testing and test preparation guidance.

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 16955
First edition
2016-06-15
Prosthetics — Quantification of
physical parameters of ankle foot
devices and foot units
Prothèses — Quantification des paramètres physiques des dispositifs
de cheville/pied et unités pour les pieds
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, 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 the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2  Normative references . 1
3  Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Requirements . 2
6 Setup conditions . 2
7  Quantification . 3
7.1 Heel, mid-foot and toe characteristics . 3
7.1.1 Procedure . 3
7.1.2 Data collection and calculations . 4
7.2 Roll-over characteristics . 5
7.2.1 Procedure . 5
7.2.2 Data collection and calculations . 6
7.3 Torsional characteristic . 7
7.3.1 Procedure . 7
7.3.2 Data collection and calculations . 8
7.4 Frontal plane characteristics . 8
7.4.1 Procedure . 8
7.4.2 Data collection and calculations . 9
8 Accessories .10
8.1 General .10
8.2 Procedure .10
8.3 Results .10
Annex A (informative) Quick reference .11
Annex B (informative) Three dimensional locus of force contact point on foot-sole .12
Bibliography .17
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 (see 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 (see 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.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 168 Prosthetics and orthotics.
iv © ISO 2016 – All rights reserved

Introduction
Three major factors contribute to foot design:
a) shape and size;
b) strength requirements;
c) functional performance.
Where
— a) is obvious and defined by the footwear,
— b) is specified in ISO 22523 referring to ISO 22675 (but is not suitable for use as a guide for the
selection of a specific ankle-foot device or foot unit in the prescription of an individual lower limb
prosthesis), and
— c) is addressed in this Technical Specification.
The AOPA group of ISO/TC 168 members between 2006 and 2009 carried out work on a method to
replace design criteria for prosthetic ankle-foot devices with compliance criteria which would be
applicable to both jointed devices and unjointed devices with elastic elements. In 2010, the working
group “Testing” convened in Seattle, Washington and decided to work on a standard, based on the work
of the AOPA group and other international groups. The vision statement was: “To develop a standard
which describes quantitative methods to evaluate or assess key performance indicators of prosthetic
ankle-foot devices which are correlated to measurable prosthesis user benefit.”
The subsequent work on this task has made it clear that it consists of (at least) two elements: firstly,
to develop a standard which describes quantitative methods to evaluate or assess key performance
indicators and secondly, to investigate and attempt to establish the correlation between these measures
and relevant measures of prosthetic user benefit. This Technical Specification describes solely the
quantitative methods to evaluate or assess key performance indicators.
The following definitions apply in understanding how to implement an ISO International Standard and
other normative ISO deliverables (TS, PAS, IWA).
— “shall” indicates a requirement
— “should” indicates a recommendation
— “may” is used to indicate that something is permitted
— “can” is used to indicate that something is possible, for example, that an organization or individual
is able to do something
In 3.3.1 of the ISO/IEC Directives, Part 2 (sixth edition, 2011) defines a requirement as an “expression
in the content of a document conveying criteria to be fulfilled if compliance with the document is to be
claimed and from which no deviation is permitted.”
In 3.3.2 of the ISO/IEC Directives, Part 2 (sixth edition, 2011) defines a recommendation as an
“expression in the content of a document conveying that among several possibilities one is recommended
as particularly suitable, without mentioning or excluding others, or that a certain course of action is
preferred but not necessarily required, or that (in the negative form) a certain possibility or course of
action is deprecated but not prohibited.”
TECHNICAL SPECIFICATION ISO/TS 16955:2016(E)
Prosthetics — Quantification of physical parameters of
ankle foot devices and foot units
1 Scope
This Technical Specification describes quantitative methods to evaluate or assess key performance
indicators of prosthetic ankle foot devices.
For each method, the set-up and test configurations are described. Also included is a variety of
parameters which are derived or calculated from the recorded data.
2  Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 10328, Prosthetics — Structural testing of lower-limb prostheses — Requirements and test methods
ISO 22523:2006, External limb prostheses and external orthoses — Requirements and test methods
ISO 22675:2016, Prosthetics — Testing of ankle-foot devices and foot units — Requirements and test methods
3  Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
heel, mid-foot and toe characteristics
physical parameters to describe the response of the ankle foot device under load after heel strike in
mid stance and prior toe off
3.2
roll-over characteristics
physical parameters to describe the sagittal plane properties of the ankle foot device relevant for the
patient during stance-phase
3.3
full contact motion
physical parameter to describe the angular range of motion of the shin where the heel and the toe are in
contact with the ground simultaneously
3.4
torsional characteristic
physical parameter to describe the rotational response of the ankle foot device under load and
additional torque in transversal plane
3.5
frontal plane characteristics
physical parameter to describe the frontal plane response of the ankle foot device during roll over on
four different tilted ground angles in frontal plane
4 Symbols and abbreviated terms
Symbols and abbreviated terms are those used in ISO 10328 and ISO 22675.
5 Requirements
To determine comprehensive ankle foot device performance and to claim compliance with this
Technical Specification, all parameters shall be quantified and the strength requirements specified in
ISO 22523:2006, 4.4, shall be met.
If an ankle foot device allows for different adjustm
...