When we stand and are fully weightbearing, the alignment of the Sub-Talar Joint is critical to the correct positioning of the feet when they are in contact with the ground.

When we stand, the three-arched foot structure must provide an upward force that is sufficient to prevent the foot from instability or collapse, but not too much that the arches remain static.

With an ideal foot alignment (i.e., no natural varus or valgus deformity as assessed with the Sub-Talar Joint in neutral), the ideal positioning of the 3 keystones - the Talus, Cuboid and Middle Cuneiform creates the most efficient arrangement of arches to oppose the force of gravity. This is when the Sub-Talar Joint is in a neutral position; neither pronated or supinated.

The effect of a natural varus footshape

With a natural varus deformity, the foot remains slightly torsionally twisted and inverted relative to the ground. When we stand, this inverted foot structure must roll inward and downard to meet the first stable object it can find - the ground.

This action forces the keystones of the three arches in the foot - the Talus, Cuboid and Middle Cuneiform out of their ideal position.

With the keystones out of alignment, the downward force of gravity is greater than the upward force that the compromised bony three-arched structure can provide. The result is an increased risk of developing lowered arches and over-use injuries of the soft tissues within and around the foot as they work harder to compensate.

The effect of a natural valgus footshape

With a natural valgus deformity, the opposite is the case. The naturally everted footshape provides a 3-arched structure that is so strong it creates an upward force that is greater than the downward force of gravity. In this case, the foot must reposition itself when in contact with the ground by rolling the outer side of the foot outward and downward to meet the ground surface.

With a valgus deformity, Sub-Talar Joint supination when standing forces the Talus into a supinated position. In this case also, the strength, stability and flexibility of the medial longditudinal arch is affected, and so in turn is that of the entire foot.