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Kevin Miller, Cped ABSTRACT The windlass mechanism of the foot
occurs when the plantar aponeurosis, which is not stretchable, reduces the
distances between the metatarsal heads and the calcaneus.
This mechanism stabilizes the foot, especially the midfoot,
allowing a rigid lever for push-off and propulsion during gait.
This tightening cannot occur however, if there is dysfunction at
the calcaneocuboid joint. The CC joint and its locking
mechanism play an important role in cases of hypermobile feet during gait.
Traditional orthotic theory of posting and “bringing the ground
to the feet” may do nothing but force the windlass mechanism to lock the
foot into an abnormal position, although functional and less painful.
This would be analogous to bracing the person with only 10-95
degrees of motion into a pain free range, which still negates function. The CC joint is a tight fitting
joint, and even a small amount of laxity can produce a decrease in the
inferior angle of the lateral column, which alters the torque converting
function of the talocrural-subtalar-talonavicular grouping.
Abnormal rotation of the metatarsals will occur, leading to
metatarsalgia, neuromas, hallux valgus, forefoot abduction, and plantar
fasciitis. Typical arch support and orthotic
theory may do nothing but block the motion of the CC joint, which may
relieve pain but does not correct the problem.
If the cuboid is permitted to hyperpronate, the windlass mechanism
may occur later in the gait stage, usually when the toes are dorsiflexed.
The theory of corrective assessment involves correction of
tarsometatarsal displacement and assessment of position.
Normalizing the foot mechanics will allow normal propulsion to
occur, and this can be accomplished via joint mobilization.
Increasing the mobility of the metatarsals and cuneiforms,
increasing the inferior angle of the fourth and fifth metatarsals and
calcaneus ensures proper midfoot function.
Often the calcaneus develops a plantigrade position, forcing the
talus to slide into an anterior position, which pushes the physiological
limitations of the joint. Orthoses fabrication using
traditional means also comes under fire.
Slipper casting with plaster does not permit for subtle yet
important fluctuations that can occur; therefore leading to an orthotic
that is improper. Standing in
foam is no better, as there is still no good control of proper position,
and the mold is made simply in the abnormal position.
Sitting and molding in foam is also not practical, as the clinician
is pushing the foot down to create the position wanted. Optical scanner measurements have shown error via no change
in pressure on the skin when the bone underneath has actually changed
position. The most correct
method would be the contact digitizer.
The author also advocates the use of thermo formable graphite
carbon in the orthotic manufacture, which is rigid and inflexible enough
to support the midfoot through the gait cycle.
This type of fabrication technique
permits normal pronation of the foot, which is crucial for the cuboid
locking mechanism to work properly. Merely
replacing the foot to reduce pain is not the correct answer. COMMENTS Current orthotic and foot
mechanical theory has been hotly debated over the past few years, and one
can always understand the argument for each side, making decision
processes even harder. Who is
right and who is not? This
article perhaps identifies why is appears everybody is right.
Our usual methods of orthoses fabrication, either non-weightbearing
slipper casting, partial weightbearing foam molds while sitting, or
standing molds, all seem to “work”, via reduced pain.
However, as the author states, we may just be placing the foot into
another abnormal position that relieves pain.
Is this wrong? It
depends on long term results, which may not happen to those we have
treated over the past 10 years for another few decades. I have seen some adverse affects of
slipper casting and forefoot posting occur fairly quickly, with
development of other regions of pain and hallux rigidus.
I learned that even subtle correction or adaptation might be more
beneficial and less harmful than trying to make a perfect correction,
which may just force the foot into a more dysfunctional position and
stress other joints/tissues. The author sites two sources for
learning the manipulations and mobilizations necessary to restore normal
foot position and mechanics, so that an orthoses can be made.
They are Principles of Manual Medicine by Phillip Greenman,
and Advanced Principles of Lower Extremity Adjusting, by
Kevin G. Hearon, DC. Foot
manipulation was also discussed in the last book I reviewed, but nothing
specific to what this author implicates.
He does not make it clear if the contact digitizing images are
necessary to determine what would need mobilized.
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