The back of the foot is called the heel, and the bone at its core is the calcaneus, the largest bone in the foot. The calcaneus sits beneath the ankle joint, bears your full body weight every time you stand, and serves as an anchor point for the Achilles tendon and the plantar fascia. Despite being a body part most people take for granted, the heel has a surprisingly complex anatomy, and it is vulnerable to a wide range of painful conditions that affect children, athletes, and sedentary adults alike.
The Calcaneus and Its Joints
The calcaneus is roughly rectangular and sits at the very back and bottom of the foot. It is the first bone to contact the ground when you walk with a normal gait. On top, it connects to the talus, the bone that sits between the calcaneus and the shinbone. Together, the talus and calcaneus form the subtalar joint complex, which is responsible for the side-to-side rocking motion of your foot. The talonavicular and subtalar joints are linked so tightly that researchers describe the entire foot minus the talus as the “calcaneopedal unit,” a single functional block that moves against the ankle mortise above it.1PubMed. The talonavicular and subtalar joints: the “calcaneopedal unit” concept
At the back of the calcaneus is a prominent bump called the calcaneal tuberosity. This is the part you can feel when you press your fingers against the back of your heel. It is the attachment site for some of the most important soft-tissue structures in the lower limb. The underside of the calcaneus is where your weight lands with each step, and its shape and density are optimized for absorbing repeated impacts over a lifetime.
The Achilles Tendon
The Achilles tendon is the thick cord running down the back of your lower leg into the heel. It forms where the gastrocnemius and soleus muscles of the calf merge into a single tendon that attaches to the back upper surface of the calcaneus.2PubMed Central. Achilles tendon complex: The anatomy of its insertional footprint on the calcaneus and clinical implications The tendon’s fibers don’t all land in one spot; they fan out across the bone, with the bulk of the fascicles attaching in the middle portion of the insertion site.3PubMed Central. Structure of the Achilles tendon at the insertion on the calcaneal tuberosity
Something that surprises many people is that the Achilles tendon and the plantar fascia on the sole of the foot share a developmental origin. During fetal development, both structures attach to the same layer of tissue covering the calcaneus. That early connection persists into adulthood: the two structures are physically continuous through the calcaneal tissue, which helps explain why tightness or injury in one often affects the other.4PubMed Central. Development of the human Achilles tendon enthesis organ
Tucked between the Achilles tendon and the back of the calcaneus is a small fluid-filled sac called the retrocalcaneal bursa. Its job is to reduce friction as the tendon slides over bone during movement. Cadaver studies show that the bursa communicates with a pocket of fat tissue in front of the tendon known as Kager’s triangle; when fluid is injected into the bursa, it spreads into the surrounding fat and up to about 1.5 cm above the top of the calcaneus.5PubMed Central. The Achilles tendon and the retrocalcaneal bursa: An anatomical and radiological study This interconnection matters clinically because inflammation in the bursa can mimic or coexist with Achilles tendon problems, making the source of posterior heel pain tricky to pin down.
The Plantar Fascia and the Heel Fat Pad
On the underside of the foot, the plantar fascia (also called the plantar aponeurosis) fans out from the calcaneal tuberosity toward the toes. It has three bands, with the central band being the most clinically significant because it plays a key role in the “windlass mechanism,” which stiffens the arch when you push off during walking.6PubMed. Variation in the origin of the plantar aponeurosis and its relationship to the origin of the abductor hallucis muscle The shape and attachment of this central band vary between individuals and between sexes, which may partly explain why some people are more prone to arch and heel problems than others.
Directly beneath the calcaneus sits the heel fat pad, a specialized cushion of adipose tissue arranged in tiny chambers separated by fibrous walls. This pad is your body’s built-in shock absorber for the heel. Its thickness matters: people with heel pain tend to have measurably thinner fat pads than people without pain. One study found that the unloaded fat pad thickness in people with heel fat pad syndrome averaged about 7.2 mm, compared with roughly 10.4 mm in pain-free controls.7PubMed Central. What do we actually know about a common cause of plantar heel pain? A scoping review of heel fat pad syndrome The thinning was more pronounced in women. A separate study confirmed that people with unilateral heel pain showed significantly decreased fat pad thickness on the painful side regardless of gender.8Pain Physician. Relationship Between Decreased Subcalcaneal Fat Pad Thickness and Plantar Heel Pain. A Case Control Study
Nerves That Supply the Heel
The heel gets its sensation primarily from the medial calcaneal nerves, which branch off the tibial nerve as it passes behind the inner ankle bone. In about 60% of people, a single medial calcaneal branch comes directly from the tibial nerve.9PubMed. Ultrasound-guided topographic anatomy of the medial calcaneal branches of the tibial nerve Despite some variability in where exactly they originate, these branches follow a fairly consistent path over the surface of the abductor hallucis muscle on the inner side of the heel.10PubMed. The medial and inferior calcaneal nerves: an anatomic study
Understanding the nerve anatomy is useful because nerve entrapment in this area is a common and frequently missed cause of heel pain, as discussed in a later section.
Plantar Fasciitis and Heel Spurs
Plantar fasciitis is the most talked-about cause of heel pain in adults. It presents as a sharp, stabbing pain under the heel, usually worst with the first steps in the morning. The underlying problem involves mechanical overload of the plantar fascia at its attachment on the calcaneus, leading to microtears that fail to heal properly. The traditional name “fasciitis” implies inflammation, but tissue studies show something different: rather than an active inflammatory process, the tissue tends to show degeneration, collagen breakdown, and calcification, making “fasciosis” a more accurate description.11PubMed Central. The plantar calcaneal spur: a review of anatomy, histology, etiology and key associations The most common underlying mechanical trigger is excessive foot pronation, which increases tension on the structures attaching at the calcaneal tuberosity.12PubMed. Painful Plantar Heel, Plantar Fasciitis, and Calcaneal spur: Etiology and Treatment
Heel spurs and plantar fasciitis often get conflated, but the relationship between them is less straightforward than many people assume. A calcaneal spur is a bony growth that develops at the point where the plantar fascia attaches to the calcaneus. Spurs show up on X-rays in roughly 45 to 85% of people with plantar fasciitis.11PubMed Central. The plantar calcaneal spur: a review of anatomy, histology, etiology and key associations But here is the catch: a high proportion of calcaneal spurs are found in people who have zero heel pain, which suggests the spur itself is not necessarily what hurts.13PubMed Central. Plantar Fasciitis With a Calcaneal Spur Spurs are also associated with obesity, rheumatoid arthritis, osteoarthritis, and forms of spondylitis, so they appear to be a marker of chronic mechanical stress rather than a standalone diagnosis.
Ultrasound has become a valuable diagnostic tool for plantar fasciitis. By measuring fascia thickness and tissue stiffness, clinicians can identify the condition with high accuracy. A study combining thickness measurement and stiffness assessment via shear wave elastography found a combined diagnostic accuracy with an area under the curve of 0.973, using a thickness cutoff of about 3.15 mm.14PubMed. Musculoskeletal Ultrasound for the Diagnosis of Plantar Fasciitis: An Accuracy and Diagnostic Yield Study In practical terms, if your plantar fascia measures notably thicker than that threshold on ultrasound and the tissue is stiffer than normal, the diagnosis is highly reliable.
Haglund’s Deformity and Posterior Heel Pain
While plantar fasciitis affects the bottom of the heel, Haglund’s deformity causes pain at the back. It involves an enlarged bony prominence on the upper rear portion of the calcaneus, right where the Achilles tendon inserts.15PubMed Central. Haglund’s Syndrome: A Commonly Seen Mysterious Condition The bump irritates the soft tissue around it, especially when rigid-backed shoes press against it. The retrocalcaneal bursa, sitting right in front of the tendon at this spot, often becomes inflamed as well. Haglund’s deformity can be identified on a standard lateral ankle X-ray, which shows the prominent posterosuperior portion of the calcaneus.16PubMed. Can We Measure the Heel Bump? Radiographic Evaluation of Haglund’s Deformity
People sometimes call this condition “pump bump” because it was historically blamed on stiff-heeled women’s shoes, though anyone wearing rigid footwear can develop it. Treatment usually starts with open-backed shoes, padding, and icing, and in stubborn cases surgery can be used to reshape the bone.
Other causes of pain at the back of the heel include insertional Achilles tendinopathy, where the tendon itself degenerates at its attachment, and noninsertional tendinopathy, which affects the tendon a few centimeters higher, in the middle portion of the cord. Retrocalcaneal bursitis can occur on its own or alongside either form. Because these conditions overlap anatomically and symptomatically, imaging is often needed to sort them out.
Heel Fat Pad Syndrome
Heel fat pad syndrome is a distinct condition from plantar fasciitis, though it produces pain in a similar location. The difference is in what is damaged: here, the fat pad itself has thinned or lost its structural integrity, so the calcaneus is no longer properly cushioned against impact. Pain tends to be more of a deep, bruise-like ache centered directly under the heel bone, rather than the arch-side stabbing of plantar fasciitis.
One study found that in people with plantar fasciitis and a normal body mass index, the fat pad on the affected foot was thinner than on the healthy foot, though the difference disappeared in people who were overweight.17SDÜ Tıp Fakültesi Dergisi. Evaluation of the Elasticity and Thickness of the Heel Fat Pad With Ultrasound in Plantar Fasciitis The fat pad also tends to stiffen with age and with repeated injury, losing some of its shock-absorbing capacity. This is one reason heel pain becomes more common as people get older: the cushion simply wears down.
Plastic heel cups can help. A study using ultrasound elastography found that a rigid heel cup reduced the stiffness of the inner fat pad layer to about 56% of its unsupported level and increased its thickness to about 138% during standing.18PubMed Central. Biomechanical Effects of Plastic Heel Cup on Plantar Fasciitis Patients Evaluated by Ultrasound Shear Wave Elastography Shoes with built-in arch support and heel cup orthotics also modestly increased fat pad thickness by an average of about 1.25 mm.19PubMed Central. Changes in calcaneal pitch and heel fat pad thickness in static weight bearing radiographs while wearing shoes with arch support and heel cup orthotics That may not sound like much, but in a structure that can be as thin as 7 mm, an extra millimeter of cushion is meaningful.
Baxter’s Nerve Entrapment
One of the most frequently missed causes of chronic heel pain is entrapment of Baxter’s nerve, the first branch of the lateral plantar nerve. This small nerve passes through a tight space between the heel bone and the muscles of the inner foot, and when it gets compressed the result is a burning, chronic pain on the medial side of the heel that is often mistaken for plantar fasciitis.20PubMed. Baxter’s nerve: the hidden culprit of chronic heel pain The clue that sets it apart is the character of the pain: Baxter’s entrapment tends to produce tingling, numbness, or a burning quality, sometimes radiating along the sole, rather than the localized morning-step pain typical of plantar fasciitis.
Because the two conditions share a similar location and can even coexist (swelling from plantar fasciitis can compress the nerve), Baxter’s entrapment is commonly overlooked. Patients who have been treated for plantar fasciitis for months without improvement may benefit from further evaluation specifically for nerve compression.
Sever’s Disease in Children
Heel pain in adults tends to involve tendons, fascia, and fat pads, but in children the most common culprit is Sever’s disease, or calcaneal apophysitis. It is the leading cause of heel pain in kids between roughly eight and fifteen years old.21PubMed. Sever’s Disease (Calcaneal Apophysitis) During puberty, the calcaneus is still growing, and its growth plate (the apophysis at the back of the heel) is softer and more vulnerable to stress than the surrounding bone. Repetitive impact from running and jumping sports irritates this growth plate, producing pain at the back of the heel that worsens with activity.
Despite the name, Sever’s disease is not actually a disease. It is an overuse condition that resolves on its own once the growth plate closes, typically in the mid-to-late teenage years. Treatment centers on reducing activity, stretching the calf and Achilles tendon, and sometimes using heel lifts or cushioned insoles. The exact mechanism of injury is not fully understood, but it is thought to involve repetitive stress and pressure on the calcaneal growth plate.22PubMed Central. Sever’s Disease of the Pediatric Population: Clinical, Pathologic, and Therapeutic Considerations Parents are sometimes alarmed by the diagnosis, but it carries no long-term risk to the bone once growth is complete.
Spondyloarthritis and Heel Enthesitis
Not all heel pain has a purely mechanical explanation. In spondyloarthritis, a group of inflammatory conditions that includes ankylosing spondylitis and psoriatic arthritis, the immune system attacks the points where tendons and ligaments insert into bone. These insertion points are called entheses, and the heel has two major ones: the Achilles tendon insertion at the back and the plantar fascia insertion underneath. Inflammation at these sites, called enthesitis, is a hallmark feature of spondyloarthritis.23PubMed Central. Ultrasound of the Heel Improves Diagnosis-Tender Entheses in the Heel Region Rarely Corresponds to Inflammatory Enthesitis in Patients with Peripheral Spondyloarthritis
Diagnosing enthesitis by feel alone is unreliable. A tender heel in someone with known spondyloarthritis may turn out to be mechanical plantar fasciitis or fat pad irritation rather than active inflammatory enthesitis. Ultrasound can help by revealing signs like increased blood flow and structural changes at the insertion site that distinguish inflammation from ordinary wear and tear. If you have heel pain that doesn’t respond to typical treatments and you also have morning stiffness in your back, a swollen finger or toe, or a history of psoriasis, it is worth asking a doctor whether an inflammatory cause could be involved.
Heel Strike, Forefoot Strike, and What Your Heel Absorbs During Running
How your foot contacts the ground while running determines how much force your heel absorbs. Most recreational runners are rearfoot strikers, meaning the heel hits the ground first. A meta-analysis of running biomechanics found that rearfoot strikers experience substantially higher vertical loading rates compared to forefoot strikers.24PubMed. Biomechanical Differences of Foot-Strike Patterns During Running: A Systematic Review With Meta-analysis Forefoot striking reduces the magnitude of impact force and the rate at which that force loads onto the leg.25PubMed Central. Effects of Foot Strike Techniques on Running Biomechanics: A Systematic Review and Meta-analysis
This does not mean forefoot striking is categorically safer. The same research shows that landing on the forefoot shifts the load onto the ankle and calf, increasing plantarflexion moment, eccentric power demands, and stress on the Achilles tendon.25PubMed Central. Effects of Foot Strike Techniques on Running Biomechanics: A Systematic Review and Meta-analysis So the trade-off is real: rearfoot striking taxes the heel and knee, while forefoot striking taxes the calf and Achilles. For runners dealing with heel pain or knee issues, gradually shifting toward a midfoot or forefoot strike may help. For those prone to Achilles tendon problems, a rearfoot strike with good cushioning may be the wiser choice.
Diabetes and the Heel
The heel is a site of particular concern for people with diabetes. Reduced blood flow and nerve damage in the feet can lead to skin breakdown over the calcaneus, especially in bedridden patients whose heels bear prolonged pressure. Calcaneal ulcers in diabetic patients can progress to osteomyelitis, an infection of the bone itself, which is notoriously difficult to treat. In severe cases, surgical removal of part of the calcaneus may be combined with specialized skin flaps to cover the wound and deliver blood supply to the area.26PubMed Central. Surgical management of a diabetic calcaneal ulceration and osteomyelitis with a partial calcanectomy and a sural neurofasciocutaneous flap
Because the heel fat pad relies on intact blood vessels and nerves to maintain its structure, diabetic neuropathy can accelerate the pad’s breakdown. This makes heel cushioning with appropriate footwear and pressure-relieving strategies especially important for people managing diabetes, even before any wound has formed.