The calcaneus, commonly known as the heel bone, is the largest of the seven tarsal bones in the foot and forms the foundation of the hindfoot. A specific, shelf-like bony projection known as the sustentaculum tali extends from the inner, or medial, side of the calcaneus. Its name, which translates from Latin as “support for the talus,” indicates its structural function. The projection resides near the upper margin of the heel bone and plays an integral role in the articulation with the talus bone situated directly above it.
Anatomy and Location of the Sustentaculum Tali
The sustentaculum tali is a distinct, horizontally oriented protrusion found on the anteromedial aspect of the calcaneus bone. This structure projects forward from the main body of the heel bone, positioning itself on the inner side of the ankle, often located roughly one finger’s width below the medial malleolus (inner ankle bone). It is composed primarily of dense cortical bone, making it a strong anchor point within the heel.
The superior surface of this bony shelf is concave, forming the middle talar articular facet, which is the site of articulation with the talus bone. This joint surface is a part of the subtalar joint, which permits movements like inversion and eversion of the foot.
A distinguishing feature on the inferior surface is a prominent groove, which acts as a passageway. This deep channel is specifically designed to accommodate a powerful tendon that travels from the leg into the foot. The relative stability of this fragment makes it a consistent anatomical landmark within the heel.
Critical Role in Foot Biomechanics
The primary mechanical role of the sustentaculum tali is to act as a supportive bracket for the talus, the bone that connects the leg to the foot. By supporting the head and neck of the talus, the sustentaculum tali helps to transmit the body’s axial load from the leg through the ankle and into the foot. This weight transfer occurs with every step during walking or running.
The bony shelf is instrumental in maintaining the integrity of the subtalar joint, the articulation between the talus and the calcaneus. The sustentaculum tali’s articular surface ensures a stable connection during the side-to-side movements of the hindfoot.
The structure is a primary contributor to the stability of the medial longitudinal arch, the main weight-bearing curve on the inner side of the foot. The support it offers to the talus prevents the collapse of the medial arch, which is a common issue in conditions like acquired flatfoot. The proper functioning of this bony projection is directly linked to efficient foot mechanics and overall gait stability.
Associated Tendons and Ligaments
The sustentaculum tali serves as a significant attachment point for several soft tissue structures, securing the ankle and midfoot complex. On its medial margin, the structure provides a strong anchor for components of the deltoid ligament, helping to stabilize the ankle joint on the inner side.
The anterior border of the shelf is the site of attachment for the plantar calcaneonavicular ligament, also known as the spring ligament. This ligament is a dense, thick band of tissue that extends forward to the navicular bone and is a major passive support for the head of the talus, thereby supporting the medial arch. The medial talocalcaneal ligament also attaches to the sustentaculum tali, further stabilizing the joint between the talus and the calcaneus.
The prominent groove on the inferior surface acts as a guide for the tendon of the flexor hallucis longus muscle. This tendon courses beneath the bony shelf as it enters the sole of the foot. The proximity of the sustentaculum tali also places it near the path of the posterior tibial artery and the tibial nerve, which are part of the neurovascular bundle that travels behind the medial malleolus.
Clinical Significance and Related Conditions
Because of its structural importance, injury to the sustentaculum tali can have significant consequences for foot function. Although isolated fractures are relatively uncommon, they are often involved in more extensive calcaneal fractures. When the heel bone fractures, the sustentacular fragment is often displaced.
This fragment is considered a reference point during surgery for complex calcaneal fractures because its ligamentous and tendinous attachments often keep it in its correct anatomical position relative to the talus. The displacement of the middle talar articular facet due to a fracture can lead to instability of the subtalar joint, which may result in long-term pain and post-traumatic arthritis if not accurately repaired.
The tight anatomical space on the medial side of the ankle means that the sustentaculum tali is related to conditions like tarsal tunnel syndrome. Swelling, injury, or displacement of the bone in this area can put pressure on the posterior tibial nerve, which courses nearby. This compression can cause symptoms such as numbness, tingling, and pain radiating into the sole of the foot.