The Foot In Motion

As the foot moves throught the stance phases of the gait cycle, it must alternate between being a mobile adapter and a rigid lever. In order to perform this function efficiently and effectively, it relies upon two things:

• the structural integrity of the three arches and their keystones;
• suitable and sufficient motions of pronation and supination generated at the Sub-Talar Joint.

The talus and calcaneus form the sub-talar joint; from which the motions of pronation and supination are controlled. It only needs one of these bones to be slightly out of alignment, and the degree and timing of these motions is disrupted.

Impact on the Gait Cycle

Excessive pronation of the Sub-Talar Joint can happen in one of two ways. Directly it is due to insufficient or excessive torsional untwisting of the talus itself (a forefoot varus where the rearfoot is ideally aligned).

Alternatively, it may occur as a result of the repositioning of the talus to compensate for insufficient or excessive torsional untwisting of the calcaneus (a combination of both a rearfoot and forefoot varus).

Either way, a pronated sub-talar joint forces the rest of the foot to over-pronate throughout the entire gait cycle.

Because the motions of pronation and supination control the timing and alternation between the two states of foot function - mobile adapter and rigid lever, any degree of natural varus or valgus deformity of the foot will directly impact foot function.