Subtalar Joint
The subtalar joint is an anatomically significant joint located beneath the talus. To clinically evaluate the range of motion of the subtalar joint, an examiner typically holds the patient's calcaneus firmly and rotates it in both directions while the joint is non-weight-bearing. One notable aspect during this evaluation is that the talus remains almost perfectly stabilized due to the rigid structural characteristics of the talocrural joint.
In a non-weight-bearing state, pronation and supination occur as the calcaneus moves relative to the fixed talus. However, during weight-bearing activities such as the stance phase of gait, the situation is reversed: pronation and supination take place while the calcaneus remains fixed to the ground.
Under these conditions, a more sophisticated kinematic pattern is required, wherein the tibia and talus function as a single unit, rotating relative to the stabilized calcaneus. This unique mobility of the subtalar joint allows the foot's position to be adjusted independently of the alignment of the ankle and tibia. This functional specialization plays an essential role in challenging scenarios, such as walking across uneven terrain, standing with a wide stance, making sharp directional changes during walking or running, and maintaining balance on unstable surfaces like a moving ship.
Joint Structure
The subtalar joint is a structurally complex joint composed of three independent articular surfaces—posterior, middle, and anterior—located between the calcaneus and the talus.
The posterior articulation of the subtalar joint is particularly noteworthy, as it accounts for approximately 70% of the total articular surface area. Some anatomical literature refers to this posterior articulation alone as the talocalcaneal joint when describing the subtalar joint.
From a structural perspective, the concave posterior articular surface of the talus interlocks precisely with the convex posterior articular surface of the calcaneus. This arrangement creates a highly stable anatomical structure resulting from the complementary shapes of the articular surfaces, the supporting ligamentous structures, the effects of weight-bearing, and the dynamic stabilizing actions of surrounding muscles.
The anterior and middle articulations consist of relatively smaller and flatter articular surfaces. While all three articular surfaces contribute to the overall motion of the subtalar joint, clinical interventions aimed at improving rearfoot mobility generally focus on the posterior articulation, which occupies the largest area.