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In Depth Tutorials and Information
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pain, first metatarsal phalangeal joint pain, anterior knee pain, iliotibial
band syndrome and other musculoskeletal injuries. This is not to suggest
that pronation is the causative factor in all these cases, but pronation
movement is often one of a number of factors implicated, and changing
one factor affecting the injured structure can produce good clinical results
in a short period of time.
Three aspects of orthotic design are critical to controlling pronation
of the foot. The biomechanical objective is to increase the supinatory
moments acting at the combined ankle, subtalar and tarsal joints
such that the pronatory moments that are causing pronation of the
foot are resisted. This increased resistance to pronation will mean
that the foot either stops pronating earlier, stops pronating with the foot
in a less pronated position, or pronates more slowly than without an
orthosis.
It is important to note that an orthosis will not and should not prevent
pronation of the foot entirely, as this could have dire consequences for
efficient and injury-free gait. In terms of effect size, an orthosis should
rarely reduce pronation by more than 30 per cent, and clinical benefits
can be observed even in cases when only very minor reductions in prona-
tion occur. Many would consider a 10-20 per cent reduction to be a
reasonable target.
Achieving this biomechanical objective involves the use of material
under the heel to increase inversion moments at the rearfoot, and arch
supports to prevent the tarsal joints dorsiflexing (and thus the medial and
lateral arches lowering). These heel and tarsal effects are entirely coupled
mechanically and thus this is a dual approach to controlling the same
event: collapse of the medial longitudinal arch of the foot.
At the heel the orthosis should cup the calcaneus both underneath
and at the sides of the heel. This reduces the space available in the shoe
for heel movement and so can help resist heel eversion (which is a key
visible feature of pronation). A wedge of material, with the thick part of
the wedge under the medial side of the heel, can be used to increase
loading on the medial plantar aspect of the calcaneus. This can increase
the inversion moment under the heel significantly and be a powerful
means of reducing the amount of heel eversion (
Figure 3.5
) and thus
resisting pronation of the foot.
In the area of the medial longitudinal arch, many clinicians become
very focused on the height of the arch support. This is important but so
too are the point at which the arch support starts and the location of the
highest point on the arch support. Ideally, the arch support should begin
two-thirds of the way between the plantar calcaneal tubercle and the
