"The human foot is one of nature's works of art and as such, it has not yet been fully recognized and explained. It will require a deal of scientific investigation before this structure is fully understood."
The foot is made up of 26 bones. There are numerous joints between these bones that allow the foot to be both a rigid lever and a shock absorber. The largest joint in the foot is the subtalar joint. Inward movement of the foot (inversion), and outward movement of the foot (eversion) occur primarily at the subtalar joint.
The ankle is a modified hinge joint. It plays a key role in transferring the forces from the foot to the leg. The ankle joint is made up of three bones, which are connected by ligaments, muscles and tendons. A strong ligament joins the ends of the tibia and fibula to form the ankle "mortis". The "dome" of the talus (the highest bone of the foot) fits inside the ankle mortis to form the ankle joint. The ankle allows movement in only one plane. It allows the foot to move upwards (dorsiflexion) and downwards (plantar flexion).
The normal end ranges of motion for the foot and ankle vary between individuals and between children and adults. The following are approximate end ranges of motion for adults:
• Inversion - 35 degrees
From a biomechanical point of view, the shoe plays a significant part in the process of walking and standing. The height of the heel as well as the thickness of the sole greatly influence the conveyance of the weight and consequently influence locomotion itself. This sphere of influence must be duly considered, particularly in cases of static deformity. A build-up of the shoe, i.e., constructing a rocker bottom must be compensated for at the heel, otherwise the relationship between the heelheight and sole-thickness in the front of the shoe will be disturbed, thus having a negative effect on the roll-over process.
The attachment of a cushion-heel also changes the roll-over process in that it acts as a shock absorber at heel strike and at the same time increases the roll-over.
HEEL-TO-TOE-ROLL FOR THE WHOLE SOLE
A heel-to-toe roll sole can be attached to the shoe to protect the ankle joint and Chopart's joint. Measured radially from the knee, this allows a complete roll of the foot.
THE USE OF INSOLES
The insole and the shoe must form a unit with the level ground. Whether the foot is neutral, in pronation or supination, is of no significance. When insoles are made of solid material, their length and shape are important. It is of particular importance with handicapped patients that the insoles are kept somewhat longer in order to reduce the risk of tilting sideways. This pronatory support, especially in the forefoot region, gives the patient a feeling of security. The correction of the talipes valgus should be differentiated from the correction of the talipes varus. With talipes valgus, the rear of the foot should be supinated and the fore-foot pronated in order to achieve a rotation of the foot. With talipes varus, this is not possible. Here, the whole foot must be pronated, i.e., the rear- and fore-foot must be included in an homogenous correction.