The subtalar joint is a complex structure within the foot that plays a significant role in movement and stability. Located deep within the hindfoot, this joint acts as a crucial link between the lower leg and the ground. Its ability to manage motion allows the foot to adapt to various surfaces and effectively absorb the forces generated during walking or running.
Anatomical Placement and Structure
The subtalar joint is positioned directly below the ankle joint (talocrural joint) in the rear part of the foot. It is formed by the connection of two large tarsal bones: the superior talus and the inferior calcaneus (heel bone).
The joint is a complex structure, featuring multiple points of contact between the two bones. The subtalar joint proper has three distinct facets—anterior, middle, and posterior—where the talus rests upon the calcaneus. These articulating surfaces are covered with smooth cartilage, which helps to minimize friction during motion.
An intricate network of ligaments provides substantial support and stability. The most prominent stabilizer is the interosseous talocalcaneal ligament, a strong band of tissue located within the sinus tarsi, a small canal between the talus and calcaneus. This ligament provides the majority of the stability, binding the two bones firmly together. The entire joint is enclosed by a fibrous capsule and a synovial membrane that produces fluid to nourish the cartilage.
Role in Foot Movement and Stability
The primary purpose of the subtalar joint is to facilitate movement that allows the foot to function effectively on uneven terrain. Unlike the main ankle joint, which controls the up-and-down motion (plantarflexion and dorsiflexion), the subtalar joint is responsible for side-to-side movements. These motions are known as inversion (sole turns inward) and eversion (sole turns outward).
This rotational capability is fundamental for shock absorption as the foot strikes the ground during gait. The subtalar joint allows the foot to pronate, a combination of movements that helps the arch flatten slightly to absorb impact forces. Immediately afterward, the joint must allow the foot to rapidly supinate, which locks the foot bones together and creates a rigid lever for pushing off the ground.
The continuous adjustments made by this joint maintain balance and prevent the body from falling when walking on sloped or irregular surfaces. The joint acts as a torque converter, translating the rotation of the lower leg into adaptive movement in the foot. This functional unit ensures that the body’s weight is distributed properly across the foot, protecting the rest of the lower extremity from excessive strain.
Common Causes of Subtalar Joint Pain
Subtalar joint pain usually manifests as a deep ache in the hindfoot, often near the heel, that worsens with physical activity or standing for prolonged periods. One of the most frequent causes of chronic pain is subtalar arthritis, which often develops years after a traumatic injury such as a severe ankle sprain or a fracture of the talus or calcaneus. This post-traumatic arthritis involves the degradation of the joint’s cartilage, leading to stiffness and bone-on-bone friction.
The joint can also suffer from instability, commonly occurring after a ligament sprain that affects the supporting structures. When the ligaments are damaged, the bones may move excessively, leading to recurring pain and difficulty walking, particularly on irregular ground. Another condition, Tarsal Coalition, represents an abnormal connection between two or more bones in the hindfoot that occurs during development. This congenital issue limits the joint’s motion, causing the foot to become overly rigid and leading to chronic pain and a rigid flatfoot in adolescents and young adults.
Other sources of pain include inflammatory conditions like rheumatoid arthritis, which can cause swelling and stiffness in the synovial lining of the joint. Sinus tarsi syndrome, an inflammation within the canal that houses the interosseous ligament, can cause localized pain just below the ankle bone. These issues compromise the joint’s capacity to glide and rotate, resulting in pain that interferes with normal walking mechanics.