Neuroscience Poster Session

Re^3: Effect Of Hinged Ankle Foot Orthoses On The Oxygen Cost Of Walking

Desiree Maltais

>Hi again Dr Maltais,

And hello again to you,

>Thank you for your reply to my question.

You are welcome. It is good to "meet" someone doing similar work to our group.

>>...  So, while we know that the oxygen cost of walking is up to 2.5 times higher in these children compared to healthy peers, we do not know enough about the extent it can be affected by any intervention; therefore we really do not have sufficient data to quanitfy any change as minimal or maximal. Moreover, we do not know enough yet about how such changes translate into changes in daily function.

>I apologise for not being clear enough on that point but my use of the word minimal was not to be used in a sense of comparaison with other manamgement modalities but more in the sense of a small change in the energy efficiency.

I appreciate the clarification. The change in oxygen uptake due to the hinged AFO was indeed small relative to the increased oxygen cost of walking in these children compared to healthy kids. I do not consider our measures (as reported here)indicative of energy efficiency  though, because we did not report the actual mechanical work done by the children when they walked. We did however collect kinematic data (to get some estimate of mechanical power) while the children walked on the treadmill. Once these data have been analised we will be in a better position to comment on effiency and any interactions between walking speed and efficiency. For now all we can really talk about is economy of walking.

>Furthermore, as you state it is not known how such changes can translate into an increase in mobility.

I suppose it has to do with how one defines and measures mobility.
I am not sure what you mean by this statement?

>I would make the hypothesis that since mobility is not a linear continuum a small number of participants would have an improvement in their daily function.

Perhaps you could clarify it for me? Thank you.

>>Now I am interested in what you term a therapeutic effect and how this is different from an orthotic effect.

>The orthotic effect is the difference between with and without the orthosis at one point in time whereas the therapeutic effects are the changes occurring over a certain time in the without orthosis condition. We investigated spinal cord injured participants with an incomplete motor function loss that were classified as chronic cases (>1 year post-injury). We measured their maximal overground walking speed, spatial-temporal and kinematics during overground walking, the walking efficiency using the Physiological cost index, a mobility scale as well as other locomotor tasks and reflex assessment using ramp and hold imposed perturbations. The objective of the study was not to compare the FES-assisted walking with any other interventions but to see what were the effect of using it. Suprisingly, all the participants had an improvement during the first year of using the FES-assisted walking  but all of the improvement was due to the therapeutic effect. Eventhough the orthotic effect changed during the intervention period on average it was equivalent to zero. But by further analysing the data it was shown that the orthotic effect was inversely correlated to the initial walking speed with the slowest walker benefiting more from the FES orthosis then faster walker, eventhough the therapeutic effect in absolute terms was higher for the fastest walker.  

So was the effect due to the residual function of the muscles  you were stimuating? In other words did walking speed correlate with some measure of muscle function? Could fast walkers (with more residual function in the stimulated muscles to start with)improve to the point of being able to do well outside of the brace, and the slow walkers (with less residual muscle function to start with)need the FES-orthosis to maintain optimal muscle length (length-tension relationship??). I could see that if the percentage gain in some measure of muscle function (compared to pre-orthosis) was the same in both groups, then outcome could still be different as you describe. What did you conclude from your results?

While most the subjects in our study were rather mild, the effects of the brace on gross motor function were most marked in the two most physically involved children. Perhaps the effect of the hinged-AFO would  be more marked in more involved children.  Although I have a hunch that for the really involved kids (household/classroom only walkers who use a rollator) the weight of the brace would increase their energy cost of walking. I wonder if there is an cetain level of mobility impairment which children must have to benefit the most from these braces? Another study for another time...

>Hence, the question I would like to see answered would be: Does Hinged AFO have a therapeutic effect that could be added to the orthotic effect that you report?

A very good question!
There was a multi-centre study out of McMaster university a few years back that tried to answer a similar question (abstract published in Dev Med and Child Neurol in ?1995 -C Evans et al.). They looked at whether the use of an AFO (so they started with young children before they received their first pair of braces and compared to control group which did not receive braces) affected the pattern of gross motor development. Their results were inconclusive. But again it is difficult to say why because-- by virtue of the age (12- 48 months) the researchers were limited in how much testing they could do. And since this the age when children first receive a brace, this is the age that testing must be done.

Orthopedic surgeons often recommend use of AFO after tendo-achilles lengthening, usually for at least one year. Although I am not familiar with any particular study, the clinical opinion seems to be that at minimum these braces enhance the "therapeutic" (out of braces) effect of other interventions. Again perhaps the interaction of brace and other interventions needs to be looked at and that might give us more information on the "therapeutic" effect as you define it.



[ Previous ] [ Next ] [ Index ]           Mon Dec 14