Dear all,
I thought I'd pass on this request from Nat Ordway. I'm afraid, since
we
only just took delivery of our Vicon, I can't help him out. We are
planning on a big data collection of Hong Kong children next month,
which I will making available on the CGA site. However, I wonder if
anyone has any data now that they're willing to share? I'm hoping that
CGA can build up a nice database in this way.
I'll be very grateful for your normative data in any format (.GCD, ASCII
etc.), and will, of course, acknowledge the source on the page.
I look forward to being avalanched!
Chris
Dr. Kirtley,
I just visited the CGA webpage and would like to say that this is a
very
good site. Good job! One thing I was looking for on your site was some
normative data (mean ± SD) for a pediatric population.
We realize that
we should create our own data for our system, but this is going to
take
some time to build up. Would you be willing to share some normative
data or
do you know of someone who could help us out? This also made me think
that
this might be a good idea for your website, a large database of normative
data based on age or other factors. I know Sutherland has books on
the
graphs for various ages, but we are looking for tabulated data
in a
spreadsheet format.
In particular, the data that we are looking for is kinematic data for
the pelvic angles (rotation, obliquity, and tilt) and hip, knee, and
ankle
angles. Thanks in advance for any input you can provide.
Nat
Nathaniel Ordway, MS, PE
Assistant Professor
Department of Orthopedic Surgery
SUNY Health Science Center
750 E. Adams St
Syracuse, New York 13210
mailto:ordwayn@hscsyr.edu
voice: (315) 464-6462
fax: (315) 464-6638
www: http://www.ec.hscsyr.edu/ortho
Just thought there might be some potential for a short teach-in here
if we could get a few
able-bodied databases together to compare. I'd offer up our .gcd file.
I assume you've got one.
I wonder if we could put a call out for others? It would be interesting
to compare them to see
how significant differences are between different Systems/Labs/Populations.
Richard
Richard Baker
Gait Analysis Service Manager
Musgrave Park Hospital
Stockman'sLane
BELFAST
BT9 7JB
Tel: +44 (0)1232 669501 ext 2155
Fax: +44 (0)1232 611064
I was concerned today to read of the request for normative gait data
for
chidren by Nathaniel Ordway. I was equally if not more concerned
by the
enthusiastic acceptance of the idea by Dr. Chris Kirtley to build up
a CGA
database.
To compare our results to someone else's data base is statistically
flawed
because it certainly won't have been validated on our own population
group.
More importantly it could be very dangerous especially if surgical
decisions
are to be made based on the analysis results.
We must realise (if gait analysis is going to develop its clinical usefulness
and scientific credibility) that we must develop our own normal data
from
which to compare our laboratory results. Why? Because we
all use different
systems with different marker sets and marker placers and we
all have
differing levels of experience in clinical gait analysis.
Comparisons with a CGA database would only be safe if we all used exactly
the same validated protocol and had carried out and reported inter
and
intra-rater reliability test results. This would be impossibly
time
consuming and far in eccess of the relatively short time that it does
take
to build your own laboratory normative data base. To do so is vital
since we
are directly responsible for the health and well-being of people's
quality
of life. Those of us that take the short cut and don't bother
to produce a
normal database for our own systems surely need to think hard!
Do I have supporters or do I stand alone?
Sorry this caused such a stir with Kim Jones and anyone else who has
these
feelings. I didn't think the request or idea was so bad. To start with,
normative data already exists in books, chapters, journal articles
and
electronic form. A database seems (or seemed) appropriate. Obviously,
this
data is dependent upon a number of factors. I don't believe the argument
that various analysis systems and/or marker sets result in different
numbers is a good one. I agree completely that this may be the case
sometimes, however this is something that needs to be worked out or
standardized so that analyses can be compared between laboratories.
I've
seen some progress in this area and expect to see more. I do not understand
how "gait analysis is going to develop clinical usefulness and scientific
credibility" if clinicians/scientists can't examine cases where the
data
wasn't generated from their lab. A database is perfectly safe as long
as
the appropriate factors are taken into consideration. As a final note,
I
haven't met a clinician yet that has made surgical decisions based
on
analysis results in comparison to normative data.
Well... at the risk of stirring up this debate even further, here's
my
response to Kim Jones' concern:
Reasons for sharing normative data
1. To check that your system is working properly (sounds trivial, but
I've visited several labs whose "normal" data is not normal!). Until
recently, for example, one famous manufacturer of 3D motion analysis
equipment didn't pick up the K4 burst in its inverse dynamics plots
(I
think they were doing some kind of static anaysis using the ground
reactions alone, ignaoring inertial effects). Nobody had ever noticed
because no normative data was supplied with the equipment.
2. To detect errors in marker attachment. Unlike Kim Jones, I do think
this should be classified as systematic error, not accepted as some
kind
of local idiosyncrasy. A joint angle is a joint is a joint angle. It
makes no sense to say that the laws of physics are different in
different labs.
3. After many years of testing around the world, Dave Winter's (2D)
data
has stood the test of time, and is just about as certain as anything
can
be in the world of biomechanics. This is not the case for some data
that
has been published in the past. In fact this list began following a
heated debate on BIOMCH-L (May '96:
http://biomch-l.isbweb.org et
seq.)
about some controversial curves (knee & hip kinetics in Kabada's
1989
study, shown in Dwight Meglan's chapter of the textbook "Human Walking")
which differed from Winter's, especially around push-off - see
Appendix
below). It eventually transpired that this (published) data was
erroneous. My point is that if these researchers had checked their
results against standard normal curves they would have noticed something
was wrong.
4. A good set of standard curves for 3D has yet to gain acceptance.
Only
by sharing our data can we achieve some form of consensus.
5. The more the better - as in the Cochrane collaboration in Oxford,
a
grouping of lots of small studies of normal subjects (and most of us
for
practical reasons usually limit ourselves to 10-20 subjects) can produce
something greater than the sum of the parts.
6. As Nat mentioned, we all know that if we are going to learn more
about gait analysis, particularly the interpretation of curves, we
are
going to have share data in some form or other. I don't believe that
Kim
is correct in saying that all labs necessarily produce different results
- but supposing they do? Wouldn't we then need a sample of normal data
from each lab before we could interpret their results? This would,
indeed, be an even more imperative reason for having a public database!
Appendix
Just to give you some idea about how different we can be. Here's a copy
of the summary I made back in May '96 of peak normal knee & hip
joint
kinetics at push-off:
moment
power
Hip
Kirtley
1.35 nm/kg flexor
1.45 w/kg
concentric
Devita et al
1.00
1.00
Winter
0.40
0.67
Rash
3.6 %BW*Ht
3.9 %BW*Ht
Abramczyk 0.34
flex
0.55 gen
Sylvie#1
0.79 (0.12) Nm/kg
Sylvie#2
0.37(0.13)
0.19 (0.09)
concentric
Dyhre-Poulsen ("as for Kirtley")
Lohmann
0.64 Nm/kg flexor
0.76 W/kg concentric
Knee
Kirtley
0.85 nm/kg extensor
4.80 w/kg eccentric
Devita et al
0.50
2.00
Winter
0.16
0.76
Rash
3.2 %BW*Ht
Abramczyk* 0.14 ext
0.69 abs (*children)
Sylvie#1
0.42 (0.08) Nm/kg
Sylvie#2
0.13 (0.09) Nm/kg
0.38 (0.24) W/kg
eccentric
Dyhre-Poulsen ("as for Kirtley")
Lohmann
0.14 Nm/kg extensor
0.85 W/kg eccentric
I think this demonstrates the need for a public database. Anyone who
doesn't want to be part of such an endeavour being, of course, perfectly
free to stand aside.
Chris
--
Dr. Chris Kirtley MD PhD
Dept. of Rehabilitation Sciences
The Hong Kong Polytechnic University
Hong Kong
Special Administrative Region of The People's Republic of China
Tel: +852 2766 6755 Fax: 2330 8656
Home: http://www.polyu.edu.hk/~rs/kirt/index.htm
PolyU Gait Lab: http://www.rs.polyu.edu.hk/gaitlab
I fully support your strong objections.
What further information would give a centralised database, apart
from confirmation or objection to the graphs published in literature?
>From personal experience (I have collected normative data for 25
normal children in test-retest evaluation) the whole system requires
a very tight, standardized marker placement protocol. In case
you
think about including EMG in your database, I wish you good luck!
I think that even within the VICON user group, creating a
centralised database would reveal considerable variability,
even
within the protocols used in Vicon labs I have seen considerable
differences.
Also, there is more out there than VCM and
I think I would like to stress once more the relevance of looking at
the underlying biomechanical model and keep an open mind to
the
effect that is introduced by "misplacing" a marker, in the particular
model that is
used. So often this is presented to people as being a black box,
although
BodyBuilder might change this.
The final question to be answered is: who is responsible for the
"abberant" curve this time: the equipment (whatever part), the
physio (most likely) or the child. At least creating your own data
base, gives you a good idea of the
first two factors involved.
In line with my concern of the effect of the biomechanical model, I
would like to launch the following concern: "What is the effect
of
extrapolating equations for joint centre determination based
on
adult data, to pediatric data?" I have seen statements
that there is
no problem to use inertia parameters determined from adult data,
because inertia is believed to play a minor role in gait, but can we
ignore
possible effects in relation to the determination of eg hip or knee
joint centre location?
Anyone out there who would like to share his views on this?
Kind Regards,
Ilse
Ilse Jonkers
Research Assistant
Ergonomics Lab (Prof. Spaepen)
Faculty of Physical Education and Physiotherapy
Tervuursevest 101
3001 Leuven
Belgium
Voice: ++ 32 16 329105/329100
Fax: ++ 32 16 329196
A propos of this current discussion, I thought you might like to see
what my undergrad students did this Summer (while I was away enjoying
myself in Europe!). They did a small reliability study on Vicon
with 20
young and elderly adult subjects. Unfortunately, due to the small size
of the lab (this is Hong Kong!) and (I think more importantly) the
proximity of the force platforms, the stride lengths and walking
velocities tended to be lower than normal, but I think the coefficients
of variation are probably still of interest. The gait curves are also
on
the page, and I've put the 'normal' data that comes with Vicon (Jim
Gage's???) on the same graphs. My students and I would be grateful
for
any comments. They documented their marker placement technique
with
lots of pictures so you can compare their technique to yours.
http://www.rs.polyu.edu.hk/gaitlab/fyp98
Best wishes for a pleasant weekend!
Chris
--
Dr. Chris Kirtley MD PhD
Dept. of Rehabilitation Sciences
The Hong Kong Polytechnic University
What I would like to point out is that there is a terribly long way
between
marker set and Flex/Exte, In/Ex and Ab/Ad rotations! OK angles
is angles,
but when talking about relative orientation of two rigid segments in
space,
the mechanical convention, the mathematical formulation, the positions
of
the axes, the reference body segments orientation, the anatomical landmarks
used should all be given and defined for the final calculation.
I don't want to say that sharing normative databases is useless. It
can
give an idea whether your data is comparable with other, but I strongly
recomend to collect and analyse your own normative database,
... unless we
all agree at least a common set of rules for the definition
of these
angles. Shareware databases of the most common protocols would be instead
of a great help, although gender, race, age source of variabilities
should
be accounted. I think it is not necessary to standardise even the data
collection, but at least get a set of definitions like 'the
flexion of the
knee is the angle around the axis joining the two femoral epicondyles'
no
matter on how your system or protocol can collect their positions in
space
during the task. We've recently found that hip joint center
can be detected
with differences among different methods up to 35 mm, how could we
talk of
common references! I believe that efforts in this direction would be
very
useful.
In summary, I do not agree that 'an angle is an angle': there are thousands
of ways to calculate and represent different segment relative positions,
even using the same marker set.
That's just my two cents experience.
Nice to talk to you all
Alberto Leardini M.Eng.
Movement Analysis Laboratory
Istituti Ortopedici Rizzoli
Via di Barbiano 1/10, 40136 Bologna ITALY
tel: ++ (0)51 6366522
fax: ++ (0)51 6366561
mailto: leardini@ior.it
Address in Oxford
Oxford Orthopaedic Engineering Centre
Nuffield Orthopaedic Centre
Windmill Road, Headington, Oxford OX3 7LD ENGLAND
tel: ++ (0)1865 227684
fax: ++ (0)1865 742348
mailto: alberto.leardini@ooec.ox.ac.uk
"But the man that is will shadow
The man that pretends to be" T.S. Eliot
I have to disagree with some of the points in what is basically a very
good and helpful email.
1. To check that your system is working properly (sounds trivial,
but
I've visited several labs whose "normal" data is not normal!). Until
recently, for example, one famous manufacturer of 3D motion analysis
equipment didn't pick up the K4 burst in its inverse dynamics plots
(I
think they were doing some kind of static anaysis using the ground
reactions alone, ignaoring inertial effects). Nobody had ever noticed
because no normative data was supplied with the equipment.
Puting a standardised set of data into a particular model, to test
that its doing what a supposedly similar model is doing, is a lot
different from actually trying to standardise general 3-D
collection/calculation methods for common data output from diferent
methodologies.
2. To detect errors in marker attachment. Unlike Kim Jones, I do
think
this should be classified as systematic error, not accepted as some
kind
of local idiosyncrasy. A joint angle is a joint is a joint angle.
It
makes no sense to say that the laws of physics are different in
different labs.
Of course they don't vary, but this isn't about the laws of physics.
All our angle definitions are to some extent arbritrary, so
what
people conform to is not normal but the accepted norm, and that
really does depend on the model you use and the marker protocol used
to achieve that model. I would re-quote and say "an angle
isn't an
angle, isn't an angle"!
4. A good set of standard curves for 3D has yet to gain acceptance.
Only
by sharing our data can we achieve some form of consensus.
In 2-D I don't think you have a problem, but in 3-D its very
complicated because of model differences, calculation order,
resulting error sensitivities etc. Whose model are you going
to force
on every one.
5. The more the better - as in the Cochrane collaboration in
Oxford, a
grouping of lots of small studies of normal subjects (and
most of us for
practical reasons usually limit ourselves to 10-20 subjects) can
produce
something greater than the sum of the parts.
Great idea, but I am sure that your SDs will be bigger than the total
expected range of most of the variables. Also I personally think it
is less important to be able to reproduce a normal curve within some
amorpohorus limits of uncertainty, than it is to be able to
reproduce a pathological set of curves, collected twice in identical
circumstances, so that the differences do not call into question the
value of the clinically relevant variables.
6. As Nat mentioned, we all know that if we are going to learn
more
about gait analysis, particularly the interpretation of curves,
we are
going to have share data in some form or other. I don't believe
that Kim
is correct in saying that all labs necessarily produce different
results
- but supposing they do?
Wouldn't we then need a sample of normal data
from each lab before we could interpret their results?
This is my personal recommendation on the subject and has been since
the issue raised its thorny head in CAMARCII. I also wouldn't
expect
anyone to take my clinical data seriously unless it was being
compared against a set of normal curves I had collected.
This would, indeed, be an even more imperative reason
for having a
public database!
No I would say it is a reason for each lab having pubicly scrutinsed
databases. It is consistency within a lab rather than some
generalised conformity which is essential.
Well there you are, chew me up and spit me out!!
Jeremy
Jeremy Linskell
Manager, Gait Analysis Laboratory
Co-Ordinator, Electronic Assistive Tehcnology Service
Dundee Limb Fitting Centre
Dundee, DD5 1AG, Scotland
tel +1382-730104, fax +1382-480194
web: http://www.dundee.ac.uk/orthopaedics/dlfc/gait.htm
Maybe referring to GCD files as DST format files would alleviate
this problem.
I will ask Tommaso Leo if it is possible for me to distribute the PGD
Lexicon manual (I don't know about the copywrite position) which
may
be of interest.
regards
Finally I would ask Dan to visit the ABCmale web site at the address
abcmale.ee.unian.it where
probably useful information and useful elements
of discussion for their interest can be found.
Regards.
Tommaso
Prof. Tommaso Leo
Dept. of Electronics and Automatics
University of Ancona
Phone: + 39 071 2204842
Fax: + 39 071 2204835, 2804334
Surface Mail Address:
Dipartimento di Elettronica e Automatica
v. Brecce Bianche
60131 Ancona-Italy
GCD files are Oxford Metrics own commercial implementation of DST
files in their Clinical Manager Sofware.
Also I have a copy of the GCD Lexicon document (version 1.1) on
disk.
Could this, or a later version, perhaps be made available at the CGA
website. This will certainly aid discussion on standardisation in
this area.
Best regards
I'm glad you like the C3dEditor and have managed to get it working OK.
The
DST file format is something that the EEC came up with from
the CAMARC project
a few years back - the idea was that it would become the standard for
exchanging data between the various labs in the EEC but it appears
to have
died on the vine. The Oxford Metrics GCD files are
a sub-set of the DST
format but that seems to be as far as it went - I don't know of any
other
products or laboratories using it. This is a pity since it seems
to be a
relatively well thought-out format.
I 've been following the CGA discussion - you write:
... The gait curves are also on
the page, and I've put the 'normal' data that comes with Vicon
(Jim
Gage's???) on the same graphs...
Which normal file was supplied with VCM? I've seen two at a site
that I
recently visited - there's one that's just called normal.gcd and a
pair called
hhhnormr.gcd and hhhnorml.gcd.
We were told in the USA that the normal.gcd file originated at the
OORC in
Oxford and is based on a three or four trials from a single subject
-
OML
should be able to confirm the origin. I'm not sure which version
of VCM was
used to generate this data.
The hhh*.gcd files were generated from normal data at the Helen Hayes
Hospital
lab - the calculations would have been done with the Kadaba/Ramakrishnan
RSX
based gait software that was in use in the majority of the US Vicon
labs prior
to the introduction of VCM. Thus this data, although a
GCD/DST format file,
was not generated by VCM but was supplied to many labs in the USA for
the very
reasons that you state in the discussion.
Hope this helps...
Edmund Cramp,
Motion Lab Systems, Inc.
4326 Pine Park Drive,
Baton Rouge, LAÝ 70809Ý USA
+1 225 928-4248 (voice, 2 lines) Note - New Area Code!
+1 225 928-0261 (fax)
For information about Motion Lab Systems please visit our web site at
http://www.emgsrus.com
Well... at the risk of REALLY stirring up this debate, here's my
response to Chris Kirtley's hard work:
The issue at hand (techanically the issue at foot) is a fundamental
one. In Newton's own words# the first law of the motion of bodies
states that:
"Everybody continues in a state of rest, or in uniform motion in
a
straight line, unless impelled to change that state by forces
impressed upon it." [reference 1]
Newton's first constraint on motion, that a body continues at rest
is
ignored by GAIT analyses, which are invariably based on Newton's
second constraint, a state of 'uniform motion'. The 'state of
rest'
is presumably grouped under the heading standing POSTURE (not
a
concern of a gait analysis discussion group).
However it cannot be inferred from Newton's first law that the
state of uniform motion is ever attained, even during gait. Thus I
suggest that the entire basis of GAIT analysis is scientifically
unproven (just another minor detail to some perhaps?). I therefore
resolutely "stand by" Kim in her appeal for more rigor.
A database may be useful, but for whom, if not for the basic research
scientist or the clinician? If it is there to simply correct
"subjective" errors such as marker placement, all well and good
for
that equipment manufacturer. But who then defines the fundamental
objective baseline..... Newton! we might all agree.
But Newton said: "Then from these forces, and from other propositions
that are also mathematical, I deduce the motion of the planets,
comets and the sea. I [merely?] wish I could derive the rest of
the
phenomena of nature from the same kind of reasoning from mechanical
principles"
I wish Chris, along with Newton and his followers all the best as he
"runs ahead" with the problem. However, I would like to echo the
words of the father of the mechanical sciences, Rene Descartes,
who
in his Third and Eighth Rule for the Direction of Our Intellegence
in
the Sciences, states that:
"In the subjects we propose to investigate, our inquiries should
be
directed, not to what others have thought, nor to what we ourselves
conjecture, but to what we can clearly and perspicuously behold
and
with certainty deduce; for knowledge is not won in any other way."
"If in matters to be examined we come to a step in the series
of
which our understanding is not sufficiently well able to
have an
intuitive cognition, we must stop short there. We must make no
attempt to examine what follows; thus we shall spare ourselves
superfluous labour."
Chris who is well attuned to hard labour is, of course, quite
correct in advising that
Anyone who doesn't want to be part of such an endeavour being,
of course, perfectly free to stand aside.
The perfectly free-standing body is THE BASIS of all
biomechanical
analysis, INCLUDING gait analysis. We are indebted to Chris
and the
group for pointing us in the right direction. Now, can anyone
actually direct me to any literature where drawing the biomechanical
free-body diagram from first principles is the actual SUBJECT
of the
paper?
While some run ahead, others might wish to return to basics.
Where do you stand on the issue?
Craig
Nevin, MSc.
Anatomical Engineer
Reference
[1] Olerick RM, Apostol TR, Goodstein DL. The mechanical universe.
# Note that Newton's own words were actually in latin.
Good morning all.
Well, well, well. We biomechanists have a tendency to take our selves
all too seriously and blow things out of proportion.
Correct me if I'm wrong, but Nat and Chris had raised the idea of collaborative
data collection. Kim jumped in with his
concerns about this and opened the proverbial can of worms. Both Nat
and Chris are obviously bright individuals and
before collaborative data collection, if at all, would have reached
some standardisation between them. If they didn't that's
their choice and their down fall.
My basic view is that you record the data, report how you collected it and how it was processed and the data developed.
As researchers or clinicians you have the right to assess the method
and the data for yourself and then either use it when
reporting your own data, as a tool to assess the quality of your own
data, ignore it, pass comment on it or simply delete it.
The choice is yours!!!
Mick Dillon
_____________________
Michael Dillon
B P&O Hons. PhD Student
Centre for Rehabilitation Science and Engineering
Queensland University of Technology
School of Mechanical, Manufacturing and Medical Engineering
GPO Box 2434
Brisbane. 4001.
Ph. +61 07 3864 2751
Fax. +61 07 3864 1469
http://www.bee.qut.edu.au/mech/staff/mdillon.html
A. Esquenazi, MD-
Director
Gait & Motion Analysis Laboratory
Regional Amputee Rehabilitation Center
MossRehab Hospital/Albert Einstein Medical Center
1200 West Tabor Rd. Philadelphia PA 19141 USA
Phone: 215 456 9470
Fax: 215 456 9631
A Member of the Jefferson Healthcare Network
Nice to hear from you. I do, of course, realise that >
That's just my opinion, as I say, though one that I've heard a lot in
my
years around the conference circuit. Noone's forcing anyone to join
the
discussion, and it may never happen. But I can't see a reason NOT to
talk. If you think I'm trying to push any sort of agenda, I'd like
to
reassure you. In a way I think that's what's been the problem up till
now - the Americans don't like to think of the Europeans setting the
standards, and the Europeans are similarly afraid of the New World.
Maybe China can mediate? :-)
Best wishes,
Chris
--
Dr. Chris Kirtley MD PhD
Assistant Professor
Dept. of Rehabilitation Sciences
The Hong Kong Polytehnic University
On the contrary my point was to promote a collaboration for standards.
I agree with you that no one has a perfect system to analyze gait yet
and
that continued colaborative work is the only way to improve and learn.
Count
me in to help in any way possible and maybe soon you will see some
of our
cases and the parameters we use to obtain and analyze as a way to promote
standards.
Keep up the great work.
A. Esquenazi, MD-
Director
Gait & Motion Analysis Laboratory
Regional Amputee Rehabilitation Center
MossRehab Hospital/Albert Einstein Medical Center
1200 West Tabor Rd. Philadelphia PA 19141 USA
Phone: 215 456 9470
Fax: 215 456 9631
Sincerely,
Best regards
Annica Karlsson
Annica Karlsson, Ph.D
student
Systems and Control, Uppsala University
PO Box 27
751 03 Uppsala, Sweden
Tel: +46 18 741 78 46
E-mail: Annica.Karlsson@SysCon.uu.se,
http://frej.teknikum.uu.se/Personnel/ack/ack.html
Concerning the latter, I am really amazed, that so many groups give
data with only these vague notions of walking speed. In EMGs, for
example, walking speed really matters a lot. But the same must hold
for kinetic data. It is really false to compare a patient at his
normal speed of 0.8 m/s with the normal data of Winter, taken at some
1.25 m/s.
At
At Hof
Department of Medical Physiology
University of Groningen
Bloemsingel 10
NL-9712 KZ GRONINGEN
THE NETHERLANDS
Tel: (31) 50 3632645
Fax: (31) 50 3632751