The sustentaculum tali is a significant bony structure within the human foot. Its name, derived from Latin, translates to “support shelf for the talus,” which describes its relationship with the main ankle bone. This shelf-like projection contributes to the structural arrangement and mechanics of the hindfoot. It is part of the anatomy that allows for standing, walking, and absorbing the forces of daily movement.
Anatomical Location and Structure
The sustentaculum tali is a horizontal projection on the anteromedial aspect, or the front inner side, of the calcaneus (heel bone). It is positioned directly beneath the talus, the bone that connects the lower leg to the foot. The superior (top) surface of this shelf is concave and covered with cartilage, forming the middle facet of the subtalar joint, which permits side-to-side foot movements.
This structure also forms the floor of the tarsal tunnel, a passageway that protects nerves, arteries, and tendons traveling from the leg into the sole of the foot. Its medial margin provides an attachment point for ligaments, including parts of the deltoid and spring ligaments. These contribute to the stability of the ankle and the arch of the foot.
Functional Role in the Foot and Ankle
The function of the sustentaculum tali involves both structural support and the guidance of movement. Its primary role is providing a platform that helps bear the body’s weight by supporting the head of the talus. This area endures high contact pressures during walking, distributing forces from the leg through the hindfoot. This support helps maintain the medial longitudinal arch, the foot’s primary shock absorber.
In addition to its weight-bearing function, the structure acts as a pulley. The underside of the bony shelf features a groove through which the tendon of the flexor hallucis longus muscle passes. This muscle flexes the big toe for the push-off phase of walking and running. The groove protects the tendon and ensures it follows an efficient path for smooth toe movement.
Common Injuries and Associated Conditions
Injuries to the sustentaculum tali are uncommon and often result from high-energy events like falls from a height or motor vehicle accidents. An isolated fracture is rare; it more frequently breaks as part of a more extensive fracture of the calcaneus. The symptoms can be misleading and are sometimes misdiagnosed as an ankle sprain, with pain localized just below the inner ankle bone (medial malleolus).
A displaced fracture can lead to several conditions if the fragments heal in an improper position. These include chronic pain, subtalar joint arthritis due to an incongruent joint surface, or hindfoot stiffness. Inflammation or bone displacement can also lead to tarsal tunnel syndrome, where the tibial nerve is compressed, causing pain, numbness, or tingling in the foot. A malunited fracture can also impinge or irritate the flexor hallucis longus tendon.
Diagnosis and Treatment Approaches
Diagnosing an injury to the sustentaculum tali requires a high degree of clinical suspicion due to its rarity and subtle presentation. While standard ankle X-rays may reveal a fracture, the view can be obscured by overlapping bones. A computed tomography (CT) scan is frequently necessary to confirm the diagnosis. A CT scan provides a detailed view, allowing a physician to assess the extent of the fracture, its displacement, and its involvement with the subtalar joint.
Treatment depends on the stability and alignment of the fracture. Stable, non-displaced fractures can often be managed conservatively with rest, ice, and immobilization in a cast or walking boot to allow the bone to heal. Surgical intervention is reserved for displaced fractures where the fragments have shifted out of place. The goal of surgery is to precisely restore the anatomical alignment of the bone and the congruity of the subtalar joint, reducing the risk of long-term complications.