CGA FAQ: Effect of walking aids

from BIOMCH-L 10/11/94
In our lab in Uppsala, Sweden, we are also working to some extend with gait 
analysis for children with cerebral palsy, and we expect this activity to 
increase in the future. We are using video cameras and a force plate. The 
use of walking aids is indeed complicating the measurement and analysis. 
Among other things it is important to make sure that the crutch or walker 
does not intefere with the force plate data. In other words the walking aids 
must not touch the force plate.

If this condition is fulfilled, my opinion is that it is still valid to use 
the normal inverse dynamic model for the estimation of joint moments and 
power at lower extremety joints, as long as the walking aid only provide 
external forces to the upper extremeties. When the computation scheme starts 
from the force plate and the calculations proceed to the ankle, knee and hip 
joints, then the external forces from a crutch will be taken care of by the 
force plate data (If 10% of body weight is carried by the crutches, then the 
force plate data will be reduced by 10%).

There are other problem that I think can be practically more important, like 
the problem of getting a child with walking difficulties to hit the force 
plate properly, especially if you hide the force plate by a math (which is 
of course desirable for other reasons). Another problem is that the joints 
of interest can be obscured by the walking aid, which complicates the 
kinematic data collection.

An area where there is a need for modification of the used model is when an 
leg orthosis is used that directly influences the load transmitted by the 
joint. In such cases I do not have any good suggestions on how to estimate 
the load distribution unless the orthosis is instrumented. We sometimes use 
moment arms of the ground reaction force instead of talking about joint 
moments. By doing this we avoid the load distribution problem, and it is 
possible to assess the effect of a knee orthosis on the varus/valgus 
inclination in this way. We have seen dramatic decreases in the moment arm 
of the ground reaction force with respect to the knee joint in the frontal 
plane as a result of using a suitable orthosis as compared to walking 
without an orthosis. The hypothesis is then that it is favourable to have 
relatively small moments arms, since this is correlated with small external 
moments and thus probably to small joint loads.

Concerning walking with crutches, we have also been doing measurements with 
the subject walking in a way so that only the crutch and not the feet are 
hitting the force plate. From such measurements we can see to what extent 
the crutch is actually used during walking. Such measurements have only been 
done on adult amputees. 

I will be glad to continue the communication with you, since we probably 
have many common interests. On thing that we are presently considering is 
measurement of postural stability of children with neurological problems. Do 
you have any experience in this area (The measurements will concerns sitting 
and standing on a force plate).

Yours sincerely

Haakan Lanshammar
* From: Haakan Lanshammar       
* Tel:  018-18 30 33 
* Fax:  018-50 36 11
************************************Dear Chris,
I was involved in the technical aspects of similar studies here in
Belfast. The surgeon who headed the project was an orthopaedic
surgeon whose name is Kerr Graham. The aforementioned has since
become Professor of Orthopaedic Surgery along the coast from you
in Melbourne. Exactly where in Melbourne I don't know off hand.
But it shouldn't be difficult to find out.
He would be the man to talk to since he has used gait analysis
(VICON system) routinely to plan corrective surgery in children
as well as analysing the effects of muscle relaxant drugs to
improve the gait in CP children (rather than surgical solutions)
If you do manage to get hold of him please pass on my best wishes!
Also, get back to me if you can't find him and I will get an
exact address.
I am fairly sure he would be most interested in your work and will
prove to be a valuable "resource".
Best wishes from a damp Ireland
Joe Murphy

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