Hi Clive,



Two parameters (among others) that are associated with base of gait are speed of gait and stride length. Did you notice if one or both of these (speed and/or stride length) increased with wear of the orthoses. One effect of orthoses on efficiency of gait is to increase speed and stride length, if the patient is walking with lower speed and stride length than what his/her non-pathological and/or symptomatic speed and stride length would be.



An other parameter is surface area contact of the plantar surface, especially at midfoot for the medial arch. Supporting the medial arch via the arch of the orthoses applies pressure on the sensory recpetors of the medial arch, which has effect to stabilize posture since there is a larger area of contact on the plantar foot with the ground surface via the orthoses. We often refer to this as bringing the ground up to the foot, whereby the ortheses has effect of creating a larger (ground) surface area of contact.



I see this often with skaters and skiers, where adding an arch pad in the skate and ski boot increases their stability, especially in turns and speed in skating. Due to the tightness of the skate and ski boot around the ankle and foot, and the nature of the event, the midfoot (arch) has little movement and very small pressure (at times none) is present under the medial arch for ankle pivot (the leg and body pivoting over the foot about the ankle) is absent. In these (skates and ski boots) the foot is positioned in dorsiflexion because of the canting present in the ankle structural component of the these skates and ski boots, but the foot does not dorsiflex.



Cheers,



Norman



	-----Original Message----- 

	From: A group for the academic discussion of current issues in podiatry on behalf of Clive 

	Sent: Thu 12/2/2004 5:57 AM 

	To: [log in to unmask] 

	Cc: 

	Subject: Changes in base of gait related to orthoses

	

	

	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?

	 

	No doubt someone has the answer - haven't you?

	 

	Clive Chapman



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