what-when-how
In Depth Tutorials and Information
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materials will be expected to reduce foot pronation (a functional foot
orthosis), whereas a lat insole made from layers of cushioning material is
intended to reduce forefoot pressures (an accommodative orthosis). As
a further complication, all of these may or may not have additional wedges
or raises under the heel and forefoot to influence foot motion and load
distribution, and the features of a functional foot orthosis and an accom-
modative foot orthosis are commonly combined.
Design of foot orthoses
A great deal of attention is paid to the shape of the upper surface of the
orthosis, especially the arch and heel areas; however, the
effective
surface
of the orthosis, that is the shape the orthosis adopts under loading, is
perhaps the most important shape to consider. This depends upon the
original shape of the orthosis, the material properties of the orthosis and
the load applied to it. Two orthoses of the same shape will function very
differently if they are made from different materials, and they will adopt
very different effective shapes.
A primary choice in the provision of orthoses is whether to use 'off the
shelf' orthoses that have a preformed shape, or whether to cast the foot
and manufacture a bespoke orthosis. Practice has changed considerably
since the 1980s, so now there is far greater use of prefabricated orthoses
than casted orthoses, with no appreciable change in clinical outcomes
being reported.
The routine use of casted orthoses is questionable. Advocates of
casted orthoses make much of the need for intimate contact between
the surface of the orthosis and the foot in order that pronation of the foot
can be best controlled. While it seems obvious that making an orthosis
to the shape of a specific patient's foot will create an improved it between
the foot and the orthosis, there is no evidence that this is the case, nor
that clinical outcomes are better from casted orthoses. It should be
remembered that the cast of a foot is taken with the foot in a static posi-
tion, whereas we know that the foot moves a great deal during gait. Also,
many manufacturers who construct the casted orthosis for the clinician
modify each cast to smooth any areas resulting from the casting process,
or to compensate for poor casting technique. This is also done to reduce
the likelihood of poor fitting (which may necessitate modifications to the
orthosis by the manufacturer). As a result, the precise contour that was
captured in the cast will be lost. There is good evidence that the precise
shape of the cast is highly dependent upon the clinician taking the mould,
so two casts of the same foot will never look the same and will often look
radically different.
