Case of the Week 9/2/99: What people said...


On the 18 month follow up the download for the right and left side is
the same. With that in mind I do have some thoughts. First of all the
question of whether the back pain is affecting the gait is an
interesting one. If I might change this around a bit, I would like you
to think about the question for a moment: Is the gait affecting the back
pain?" I will go out on the limb here and say it looks like a right
sided back pain. Although I would like to have more information on this.
I notice a couple of things. When the body starts going over the right
limb, there appears to be a saggital plane blockade that is either a
lack of dorsiflexion of the ankle or a functional hallux limitus.The
body leans foward and then the body seems to "drop " on the left foot.
Its hard to tell but I would also look for a shorter left limb on this
patient. Also there appears to be an arm swing on the right that is
originating from the elbow, not the shoulder. I have also seen this on
the longer side limb especially with a back pain patient. I would be
curious if there is any upper extremity complaints as well.


Dear Henry, and others interested,

Thanks for your comments. It so happens that I can confirm your observations, since as you probably noticed, I used a full-body marker set on this patient and could therefore calculate the displacement of the body center of mass (using Michael Eames & Richard Baker's COMpost BodyBuilder model: /bodybuilder). The graph nicely shows exactly what you suggest - the body dipping down at left inital contact.

I have made animated GIF of the right side video together with the centre of mass graph, which you can now see at:


Click on the gif to get the QuickTime movie. I've also corrected the link for the left-side movie - thanks for letting me know.  I can confirm that she had a 1 cm shortening of the left. As far as the arm-swing is concerned, I guess I would have to do inverse dynamics to test your hypothesis that the swing originates from the elbow, not the shoulder - I have the arm kinematics, so I will see what I can do.

By the way, here in Europe, I'm very impressed by the speed of the Vienna mirror, which is much better than the last time I visited (apparently due to recent German internet cabling), so if you've not tried it I recommend you do so:

Chris Kirtley (von Duesseldorf, post-Altweiberfastnacht)

I've managed to do an inverse dynamics analysis of the arms to get the
ebow and shoulder joint powers, and it seems to show the shoulder and
elbow pretty much acting together on the right. I don't know what that
means, but it looks nice!:


I know the units of the powers are weird, by the way - this is a
BodyBuilder idiosyncracy.

I wonder if anyone else has done this sort of analysis on the
upper-limbs in CP? The funny behaviour we often see in the arms has been
bothering me for some time, so it's nice to see it being discussed.


Sensorimotor Laboratory
Sektion kybernetische Psychologie und Psychobiologie
Heinrich-Heine Univ.,

I did see that you did both arms. I know what the graphs show but
somehow it looks different to me on the video. I think the arm swing or
lack of it has some meaning. I am still trying to understand it better
so I can't give any real information at this time that I feel confident



I have spent considerable time recently trying to get Bodybuilder kinetics models working (for lower
limb) and so far have failed. I'm not sure whether the fault lies with me or BodyBuilder but I'm
becoming more and more convinced that it is BodyBuilder. Not to put too finer point on it I wouldn't
trust any kinetic analysis until I can see a model which replicates VCM output and OM would appear
to be quite some way from this at present.

Richard Baker

Richard Baker
Gait Analysis Service Manager
Musgrave Park Hospital

Tel: +44 (0)1232 669501 ext 2155
Fax: +44 (0)1232 68381

My thanks to Richard Baker for pointing out that my modelling of the
upper-limb inverse dynamics may well be erroneous, thanks to some bugs
in the BodyBuilder kinetics. I have instead used my trusty old 2D
digitiser software to calculate them, and I've put the results
(QuickTime movies 1.1 Mb) at:


It is interesting that, while on the left the elbow and shoulder powers
are in synchrony, with the elbow flexors more powerful, on the right the
shoulder flexors contract earlier and more powerfully.

I hope Henry can help us make sense of this new data, and apologies for
the earlier misleading results. As I mentioned, I think it's good that
we're looking at the upper-limbs at last, and I do hope something comes
out of this.

Chris Kirtley

Sensorimotor Laboratory
Sektion kybernetische Psychologie und Psychobiologie
Heinrich-Heine Univ.,

Dear Chris,
I have looked at what you sent to me over and over again.
Lets try to piece this together. When the body tries to move over the
right limb there is some flexion of the body foward over this limb.
To me there is a saggital plane blockade as I mentioned before. The left
arm and shoulder swing is much more powerful than the right. Can
it be that in order to overcome the blockade and move the body over the
foot, the left arm and shoulder movement have to "help" in this effort?
I would be curious to see this in other patients. I will keep my eyes open. Just to
add a little more confusion to this patient, the left heel appears to
stay on the ground even longer than the right?


Dear Henry,

I like your reasoning - I think you're correct that the
arm is giving some clues. I've been wondering about this for some time,
as these CP cases often show very abnormal arm swings - see, for example:


It's particularly noticeable with this case how much the elbow flexes in her case, isn't it?


Dear Chris,
 I looked at the first 3 cases you sent me and they all do the same thing. On the leg that has
the blockade the opposite arm swings much more. Also the foot with the
"uncompensated equinis" is the same side as the saggital plane blockade.
The last 2 cases did not have the same type of gait. The arms seemed
more symmetrical.


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