Subtalar joint motion (closed chain)

The figure illustrates closed chain (talar and calcaneal) movement in the right subtalar joint. In a closed chain activity like walking, subtalar motion links foot motions with motions at other lower extremity joints.

PRONATION

SUPINATION

CALCANEUS

everts

inverts

TALUS*

plantar flexesadducts

dorsiflexesabducts

TIBIA

rotates internally

rotates externally

KNEE

flexes

extends

*We typically use terms like adduction or plantar flexion to describe motion at a motion, not motion of a bone like the talus. In this usage, "adduction" and "plantar flexion" describe movement of the talus' anterior portion. In subtalar pronation, the talus' anterior portion moves inferiorly (talar plantar flexion) and medially (talar adduction).

Some students are initially concerned when they read that the talus plantar flexes and adducts during closed chain pronation. Because they know that open chain pronation has components of dorsiflexion and abduction, they wonder if open and closed chains motions occur in opposite directions.

However, open and closed chain subtalar motions, like pronation, are exactly alike at the subtalar joint surface.

In a closed chain, the talus is mobile while the foot's distal part (the "forefoot") is fixed by its contact with the ground. The mobile talus plantar flexes and adducts (its anterior part tips inferiorly and medially).

During open chain pronation, the talus is fixed, so the mobile forefoot dorsiflexes and abducts.

These motions are identical. They differs only in whether the forefoot moves on a stable talus, or the talus moves on the stable forefoot.