The calcaneus, or heel bone, forms the foundation at the rear of the foot. It is the largest of the 26 bones in the human foot. This bone is integral to bipedal movement, transferring the majority of the body’s weight from the leg to the foot.
Anatomical Structure and Location
The calcaneus is the largest of the seven tarsal bones, which make up the midfoot and hindfoot. Its shape is irregularly cuboidal, located in the hindfoot directly beneath the talus bone. This structural relationship forms the subtalar joint, which is essential for foot movement and stability.
Superiorly, the calcaneus articulates with the talus, while anteriorly, it connects with the cuboid bone, a key component of the midfoot. One of its most distinctive features is the calcaneal tuberosity, which projects backward to form the palpable prominence of the heel.
This posterior surface provides the insertion point for the Achilles tendon, which connects the calf muscles to the heel. On the plantar, or bottom, surface, the medial process of the calcaneal tuberosity is the primary origin point for the plantar fascia. This fibrous band extends toward the toes and plays a significant role in supporting the arch of the foot.
Essential Role in Movement and Support
The primary function of the calcaneus is to bear and distribute the body’s weight during all activities, from standing to running. It acts as the initial point of contact with the ground during the heel-strike phase of walking and running. This contact subjects the bone to significant vertical forces.
The calcaneus is uniquely structured to perform this demanding task, featuring an internal, spongy network of trabecular bone that acts like a natural spring system. This internal structure helps to dissipate impact forces traveling up the leg, momentarily compressing under load before returning to its original shape. It also works in conjunction with the heel fat pad, a specialized cushion of fibroelastic tissue beneath the bone that absorbs up to 80% of impact forces.
The bone also functions as a powerful lever arm for the calf muscles, particularly the gastrocnemius and soleus muscles, which form the Achilles tendon. When these muscles contract, the calcaneus acts as the fulcrum to lift the heel off the ground. This mechanism provides the necessary propulsion for walking, running, and jumping, making the bone fundamental to locomotion.
Common Conditions Affecting the Calcaneus
Due to its role as a shock absorber and weight-bearing foundation, the calcaneus is susceptible to several common conditions, mostly related to repetitive strain or high-impact trauma. Calcaneal fractures, while relatively uncommon compared to other foot fractures, typically result from high-energy events such as falls from a height or motor vehicle accidents. The force from the impact drives the talus bone down into the calcaneus, often causing complex fractures that affect the subtalar joint.
Many cases of chronic heel pain involve the soft tissues that attach to the calcaneus. Plantar fasciitis, one of the most frequent causes of heel pain, involves inflammation of the plantar fascia at its origin on the underside of the heel bone. Excessive strain on this attachment site can also sometimes lead to the formation of a heel spur, which is a bony growth protruding from the calcaneus.
Pain at the back of the heel is often associated with Achilles tendonitis, an inflammation of the Achilles tendon where it inserts onto the posterior surface of the calcaneus. This condition is common in individuals who engage in activities that involve repeated pushing off the foot, stressing the tendon fibers at their connection point. Other conditions, such as Haglund’s deformity, involve the formation of a bony enlargement on the back of the calcaneus, which can irritate the Achilles tendon and the surrounding bursa.