>I use semi flexible polypropylene orthoses
and see a lot of marathon runners and triathletes who do Ironman
distance i.e. with a half or full marathon at the end.  They obviously
get very sweaty but also get blisters when they are training at the
individual events.  Sometimes the blisters occur under the navicular or
more distal up the 1st MPJ, regardless of whether the orthotic has a
full length top cover/ extension.  I even get blisters myself when I run
sometimes and was interested in Bruce Williams theory that the medial
control in the running shoes may be the cause and be creating a Fhl type
problem.  I certainly wear a anti pronatory type shoe with my orthotics.
I previously got anterior shin pain with a neutral shoe and the same
orthoses.<


Jacqui,

If these runners get blisters as far proximally as the navicular then
perhaps the midtarsal joint was supinated in the cast, causing an increase
in the medial arch height of the orthosis.  This would cause increased
pressure at the navicular.  If the STJ was inadvertently casted supinated
rather than neutral, this can have a similar effect by increasing the arch
height.

Three options come to mind.  The first is to modify the cast by adding
additional filler in the medial arch so as to lower the entire medial arch
contour of the device and then modify or make a new device.  The second
option is to add accommodation only at the pressure sites.  The third option
is to recast the patient being certain to apply an adequate dorsiflexion,
abduction, and eversion force to the forefoot during casting to assure the
forefoot is fully pronated at the MTJ.

The blisters under the 1st MPJ may be due to insufficient forefoot valgus
correction in the device.  If the patient has an everted forefoot to
rearfoot relationship, then it is important to incorporate forefoot valgus
support in the orthosis and possibly in a top covered extension on the
device so as to increase the dorsiflexion force under mets 2 through 5 in
order to reduce the load sub 1st.  You can also use a korex (cork/rubber)
valgus forefoot extension with an accommodation sub 1st to further get the
load off the 1st MPJ area.  Also make sure that the forefoot of the orthosis
is narrow enough so as not to restrict 1st ray plantarflexion or it may be
acting to create a functional hallux limitus type situation.

Respectfully,
Jeff Root

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