Custom Calibrated Shell Flexibility
The Missing, Essential Custom Component

 

 

 

 

The amount of force an orthotic needs to deliver to the foot depends on the forces coming down from that particular body and the inherent structural stability (flexibility) of the individual foot. When the shell support is properly customized it should allow a net small, functional amount of pronation after heel strike.

 

 

 

 

 

 

 

 

Digital calibrator developed by Sole Supports (above) and detail of orthotic in the test chamber with pin sensor aligned
to the Calibration Reference Point.

 

One of the most hotly debated questions in orthotic
foot management is: should an orthotic be rigid or
flexible? Of course, to pose the question like this is to
imply that they should either always be rigid or always flexible. The question, as such, is entirely misstated.
The pertinent question is: how much supportive force
should an orthosis supply to any particular foot? The
answer to that question is a custom factor for every
foot. People who weigh more need more support
to overcome their added weight; feet that are more
flexible need more support because the inherent
structural stability is less; people who are more active
need more support to resist higher impact loading.
This should be intuitively obvious, yet the battle
between the rigid and flexible orthotic prescription
camps continues.

This is largely due to three things:

1) the lack of reliable methods for determining
the custom amount of force necessary;
2) the lack of function-based analysis or agreement
about the corrective goal for foot posture;
3) the lack of agreement on how and where to
deliver the corrective force to the foot.

We have answered numbers two and three elsewhere:
MASS position is the logical corrective goal and full,
custom-shaped contact to the plantar foot is how to
deliver the corrective force. The answer to number one
is evaluating foot flexibility, recording body weight and
activity levels as custom data on the order form, and
custom calibration that accounts for these custom
factors during orthotic manufacture.

The orthotic industry has been content to ignore these
custom factors largely because, to account for them,
the entire process of custom orthotic data collection
and manufacture would become much more
complicated and expensive. They have also been very
willing to continue Neutral STJ Position technology
because it is a useful excuse to maintain the simplicity
and profitability that technology dictates. With our
new methods and goals, however, Sole Supports has
had to be the first to develop entirely new processes in
order to create a truly custom orthotic.

One of the most important inventions in our new way
of doing orthotics is the calibration device. Actually
there are two proprietary devices we developed
to arrive at custom, calibrated shell flexibility. The
first is a device that creates a “calibrator reference
point” (CRP) on the bottom of every plastic shell.
This insures that the calibrator is always evaluating
the same point on the orthotic, both for re-tests of
the same orthotic and for new pairs. The second
and most complex device is the calibrator itself. This
device uses a pin placed directly under the CRP whose
deflection is computer monitored in thousands of an
inch increments. An air bladder is designed to envelop
the orthotic surface from above and uniformly push
the orthotic shell downwards to simulate actual foot
loading of the shell during stance phase. How much
shell deflection at what amount of force gives us a
number that determines the correct amount of shell
flexibility for that patient’s weight, foot flexibility and
activity level.

Before we were able to match calibrator numbers to
patient variables, a large amount of actual case data
were collected. The data produced a scatter graph
that suggested a predictable line or data trend that
could be used to complete the algorithm. Currently,
we are the only lab working on this level of engineering
problem-solving to deliver a more custom and
functional orthotic.