The human foot is an intricate biological structure, comprising 26 bones, 33 joints, and over 100 muscles, tendons, and ligaments. The posterior-most portion of this structure serves as the body’s initial point of contact with the ground during walking. This area, commonly referred to as the heel, is deeply specialized. Understanding its structure and function is important because it bears the greatest load and is foundational to human movement and stability.
The Heel and the Calcaneus
The common term for the back of the foot is the heel, which anatomically refers to the prominence at the posterior end of the foot. The primary bony structure forming this prominence is the calcaneus, often called the heel bone. The calcaneus is the largest of the seven tarsal bones and the biggest bone in the entire foot, designed to withstand significant compressive forces.
This bone serves as the foundation for the entire hindfoot, articulating superiorly with the talus bone of the ankle joint. The calcaneus is distinct from the ankle joint itself, which is formed by the tibia, fibula, and talus, and is responsible for up-and-down movement of the foot.
Essential Supporting Anatomy
Beyond the bone, the back of the foot relies on a system of soft tissues, including the powerful Achilles tendon. This is the thickest and strongest tendon in the body, connecting the calf muscles—the gastrocnemius and soleus—to the back of the calcaneus. The Achilles tendon acts as a lever arm, allowing the calf muscles to pull on the heel bone to facilitate plantar flexion, which is necessary for activities like walking, running, and jumping.
Beneath the calcaneus lies the specialized heel fat pad, which acts as the body’s primary shock absorber. This structure consists of chambers filled with adipose tissue, encased by tough, fibrous septa. The fat pad absorbs a substantial percentage of the impact forces generated during heel strike, protecting the bone and surrounding structures from damage.
Fluid-filled sacs called bursae are also located in the heel region to reduce friction between tendons, ligaments, and bone. Specifically, the retrocalcaneal bursa sits between the Achilles tendon and the posterior surface of the calcaneus. This bursa allows the tendon to glide smoothly over the bone, ensuring unrestricted movement.
Common Ailments of the Heel
Due to the extreme forces it manages, the heel is a frequent site of pain and injury. Plantar Fasciitis is one of the most common issues, involving the inflammation of the plantar fascia, a thick band of tissue running from the calcaneus to the toes. Pain is typically felt on the underside of the heel and is often most severe with the first steps taken in the morning or after periods of rest.
Another prevalent ailment is Achilles Tendinitis, which is inflammation of the Achilles tendon where it attaches to the back of the calcaneus. This is often caused by repetitive stress or overuse, such as a sudden increase in running mileage or intensity. Haglund’s deformity, sometimes called a “pump bump,” is a bony enlargement on the back of the heel bone. This prominence can irritate the surrounding soft tissue, including the retrocalcaneal bursa, due to pressure from rigid shoe backs.
Damage to the heel fat pad itself can cause deep, bruised-like pain under the heel, a condition known as heel fat pad syndrome. This occurs when the pad loses its natural thickness or elasticity, often due to aging or chronic high-impact activity.