what-when-how
In Depth Tutorials and Information
How load is distributed under the foot, and thus which sites experience
high pressures, is clearly related to the movement and position of the
foot. A pronated foot will tend to distribute load more medially under the
forefoot. This will load the first metatarsal head the most and, depending
upon its ability to dorsiflex in response to the increased load, could result
in very high metatarsal head loads. If the first metatarsal is able to dorsiflex
under the load applied to its plantar surface, this dorsiflexion may reduce
the loads at this site but cause the second metatarsal head to bear more
load. The second metatarsal is less mobile than the first and is unlikely
to be able to dorsiflex to the same degree, and thus will be subjected to
high load. Likewise for the fourth and fifth metatarsal heads in a foot which
adopts a supinated position and bears more load on the lateral side of
the forefoot: the fifth will bear the majority of the load but may dorsiflex
to such an extent that the load is redistributed to the less mobile fourth
metatarsal head.
Thus, intra-articular joint contact area and pressures, the magnitude,
timing and speed of forces experienced by ligaments, joint capsules,
tendons and muscles, and the contact area, magnitude and timing of
loading of specific sites under the foot can all be affected by use of
foot orthoses. These effects underpin the theoretical basis of foot orthosis
practice but in many cases are difficult or impossible to measure with
current techniques. They are highly interdependent and this means
that studying the biomechanical effects of foot orthoses to better under-
stand their precise mechanisms of action is very complex. While we
have many reports on the effects of orthoses in the literature, explaining
variation between people in their clinical and biomechanical response
eludes us.
It should be remembered that the foot is the interface between the
rest of the lower limb (and body) above and the floor below. As such,
changes in its function and mechanical behaviour will inevitably influence
the mechanics of the knee, hip and more proximal segments. Transverse
plane motion of the tibia (shank) is coupled with foot pronation and
supination and so changes foot motion will influence tibial transverse
plane rotation and thus may affect knee and hip biomechanics. It
follows that the biomechanical behaviour of these structures can also
influence the foot, and therefore the response to a specific orthotic
intervention.
Controlling pronation of the foot
Changing the pronation movement of the foot is reported to have consis-
tent clinical benefits for those with heel pain, shin splints, Achilles tendon
