11/04/2013    Jeffrey Root

Subtalar Arthroeresis Gone Bad? (Eugene A Batelli, DPM)

I believe Dr. Batelli made an important point when
he implied that other deformities (i.e.
conditions) may be creating an additional
pronation moment that is acting at the subtalar
joint and therefore on the implant. From the X-
rays it appears that the patient may have a
metatarsus primus elevatus and/or a forefoot varus
(forefoot supinatus?) position of the forefoot. If
the implant successfully limits the range of
subtalar joint pronation, then it could create an
uncompensated or partially compensated forefoot
varus condition.

In other words, the patent may need additional
subtalar joint pronation to bring the medial
aspect of the forefoot down to the ground. If the
medial aspect of the forefoot isn't bearing
sufficient weight and remains inverted to the
supporting surface, then this can create a
retrograde pronation moment at the subtalar joint.
If the patient appeared to have midfoot collapse
then I might suspect midtarsal joint instability
or hypermobility as a potential cause. But this
does not appear to be the case from the X-rays.

It is important to note that there are hundreds if
not thousands of “subtalar joint neutral device”
prescription combinations and permutations that
can be considered for this patient, so the fact
that one (or more?) orthoses have failed doesn’t
necessarily mean that all devices made from a
neutral position cast are destined to fail.

The objective of orthotic therapy in this case
would seem to be to reduce pronation moments at
the subtalar joint. In order to do so, it helps to
determine the source or sources of those pronation
moments. Without knowing more about this
individual patient’s biomechanics it is impossible
to know the source but uncompensated forefoot
varus/supinatus and equinus are two possible
causes. In any case, the orthotic Rx should be
designed to decrease the pronation moments at the
subtalar joint.

Some functional orthotic options designed to
reduce subtalar joint pronation moments include
plantarflexing the 1st ray or the medial column
during casting, correcting the heel in an inverted
position, using a medial heel skive (Kirby skive),
using a deep heel cup or a deep medial heel cup,
supporting intrinsically or extrinsically the
inverted position of the forefoot if forefoot
varus is present, increasing the medial arch
height of the orthotic shell by reducing the
medial arch fill, using an extrinsic rearfoot post
with no motion, using a heel lift to address
equinus, and so on. It is also important to note
that correcting the heel, and therefore the entire
cast inverted, will also increase the height of
the medial arch provided that lab doesn’t add
extra arch fill in the process. There are many
logical prescription modifications that can be
utilized to address the specific biomechanics of
the individual patient. Perhaps prior to removing
the implant, a different functional orthotic
prescription can be considered.

Mr. Jeffrey Root, jroot@root-lab.com

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