Kevin, Kevin and Norman,
Could you please elaborate on the subject in regard to sensory perception and stability in gait. I have found myself, that, even by introducing in a child a silicone foot orthoses improves stability with little mechanical intervention. Your thoughts around this subject and anyone else's would be greatly appreciated
regards
Tony Achilles
________________________________
From: A group for the academic discussion of current issues in podiatry on behalf of Kevin Kirby
Sent: Thu 02/12/2004 17:51
To: [log in to unmask]
Subject: Re: Changes in base of gait related to orthoses
Clive and Colleagues:
Clive wrote:
<<I have observed that in some patients there is a significant change in the base of gait when wearing orthoses. Particularly a reduction in a wide base of gait associated with profound (10 degress or more) forefoot valgus.
I saw an example of this yesterday when teaching essential biomechanics to a group of physiotherapists. In the process of the day I earmarked one of the physios as a good subject for me to use to demonstrate examination and treatment with chairside orthoses. She had B/15 degrees forefoot valgus/10 degreees rearfoot varus/ functional hallux limitus. When she walked the building shook at heel strike and she had a base of gait that was, at 30 cm, the same as her base of stance. She walked with a "stomping" gait which looked agressive. There were no symptoms other than residual pain from a 3 month old right ankle injury.
I made devices as follows; B/rearfoot 15 degrees varus/ forefoot 5 degrees valgus/ kinetic wedges. By the time she had walked 10 metres wearing the orthoses the base of gait has reduced to about 5 cm, there were some postural changes which she said felt good, the heel strike was not heavy and the walking suddenly was less agressive and stomping, the ankle pain had gone.
All that being as it may, it is not that unusual - except for me, the huge reduction in the base of gait. I can't work out why that should happen (and I have seen from a less wide base it other patients who have forefoot valgus).
Is it that the lateral instability of the feet demands a wider base of gait for more stability in walking? When people are drunk they appear to use a wider base of gait as a help in not falling down, is this similar? Is it a sensory-postural-motor compensation for the lateral instability arising from the valgus forefoot?>>
I have been thinking of writing a newsletter about this phenomenon for some time. I have also noticed this effect of a narrowing of the base of gait in feet with "rigid forefoot valgus". Interestingly, this narrowing of the base of gait is even more pronounced in many patients with multiple sclerosis, when a forefoot valgus wedge is added to shoe insole.
Here is my short synopsis of my theory that I will publish likely in the next few months in a coming Precision Intricast Newsletter. Bipedal gait requires that the center of mass (CoM) always stay within the medial-lateral boundaries of the center of pressure (CoP) of the feet in order to allow bipedal walking gait stability. If the CoP is more medially located on the plantar foot, such as from a relatively rigid plantarflexed first ray, then the individual must abduct their hip more during walking in order to bring their CoP more lateral to the CoM in order to improve bipedal stability during walking gait. Using a valgus forefoot wedge will move the CoP more lateral which will then not require the individual to abduct their hip as much to move their CoP to a more lateral location relative to their CoM in order to improve bipedal stability during walking gait.
Forefoot valgus wedges will also increase the stride length compared to forefoot varus wedges in most individuals, as Simon Spooner, Tony Achilles and Chris Nester have been shown on their own feet. However, this is another theory, maybe for some other paper or newsletter.
Cheers,
Kevin
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Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
Voice: (916) 925-8111 Fax: (916) 925-8136
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