A heel spur shows up on a standard lateral (side-view) foot X-ray as a bright white, bony projection extending from the bottom or back of the calcaneus, the large bone that forms your heel. The classic plantar heel spur looks like a small triangular shelf of bone tapering to a point, jutting forward along the sole of the foot. Posterior spurs, by contrast, stick up from the back of the heel near the Achilles tendon. What the spur actually looks like in finer detail, though, tells a radiologist more than just “there’s extra bone here,” and the story gets more interesting the closer you look.
The Classic Plantar Heel Spur
On a weight-bearing lateral X-ray, the most common type of heel spur appears as a triangular bony projection on the underside of the calcaneus, pointing toward the toes. A well-developed, or “simple,” spur tapers from a broad base at the heel bone to a sharp point. Its edges look smooth and well-defined, with a thin bright line of cortical bone (the hard outer shell) enclosing internal bone structure that follows the same organized pattern you’d see in the calcaneus itself.1PubMed Central. The plantar calcaneal spur: a review of anatomy, histology, etiology and key associations In plain terms, a simple spur looks like a clean, miniature horn of bone growing off the heel. It stands out easily against the darker background of soft tissue on an X-ray because bone absorbs X-rays and appears white.
The size varies quite a bit from person to person. Some spurs are barely a few millimeters, almost like a tiny bump on the calcaneal outline that you could miss if you weren’t looking. Others extend well over a centimeter forward from the heel. Despite the dramatic look of a large spur, the size alone doesn’t always predict how much pain someone is in, though the relationship between spur dimensions and symptoms is more complicated than “bigger equals worse.” More on that below.
Posterior Heel Spurs and Haglund Deformity
Not all heel spurs grow on the bottom of the foot. A posterior heel spur develops at the back of the calcaneus, near where the Achilles tendon attaches. On a lateral X-ray, this appears as a bony bump projecting upward or backward from the upper rear surface of the heel bone. When this bony enlargement is especially prominent, it’s called a Haglund deformity. Radiologists look at a few specific angles on the X-ray to assess whether the bump qualifies as a true Haglund deformity, including the Fowler-Philip angle.2PubMed. Association of Haglund Deformity Size and Insertional Achilles Tendinopathy
Haglund deformity often shows up alongside two other problems: inflammation of the bursa that sits between the Achilles tendon and the bone (retrocalcaneal bursitis) and degeneration of the tendon itself at its insertion point. Together, these three findings form what’s sometimes called “Haglund syndrome.”3Radiographics. The Heel Complex: Anatomy, Imaging, Pathologic Conditions, and Treatment The bursitis and tendon changes aren’t always visible on a plain X-ray, though. You can see the bony bump clearly, but the soft-tissue swelling around it is often subtle on radiographs, which is one reason doctors sometimes order ultrasound or MRI when they suspect this triad.
Smooth Versus Irregular Spurs
The texture and outline of a heel spur on X-ray carry diagnostic meaning that goes beyond simple “present or absent.” A smooth, well-organized spur with clearly defined cortical borders and visible internal bone structure is considered a simple or mature spur. This is the kind that has been developing slowly over time. It suggests a chronic, stable process.1PubMed Central. The plantar calcaneal spur: a review of anatomy, histology, etiology and key associations
An irregular spur, by contrast, looks more ragged. Its borders are poorly defined and fuzzy rather than crisp, and the internal bone pattern is disorganized or absent. This kind of appearance can suggest a more active or aggressive process. In some cases, irregular-looking spurs with a “fluffy” appearance to the surrounding periosteum (the membrane that covers bone) may point toward an inflammatory condition rather than simple mechanical wear. That distinction matters because the treatment path for inflammatory disease is quite different from the treatment for ordinary plantar heel pain.
Two Types Based on Where They Sit
Researchers have also classified plantar calcaneal spurs based on their exact position relative to the plantar fascia, the thick band of tissue on the sole of your foot. Type A spurs sit above the plantar fascia insertion, while Type B spurs form within the fascia itself.4PubMed. Classification of Calcaneal Spurs and Their Relationship With Plantar Fasciitis On a high-quality lateral X-ray, an experienced reader can sometimes distinguish these two positions, though it can be difficult without additional imaging. The classification is relevant because the two types appear to correspond to different stages of plantar fasciitis severity.
Shape categories have also been used to describe plantar spurs. Some are essentially horizontal, projecting straight forward. Others curve downward, forming a hook shape. Still others are vertical or point at an oblique angle. One study found that patients whose spurs were horizontal or hooked responded best to conservative treatment, with the greatest improvements in function and pain.5PubMed. Relationship and Classification of Plantar Heel Spurs in Patients With Plantar Fasciitis The practical takeaway is that spur shape may help predict outcomes, though clinicians don’t yet use shape classification as a routine decision-making tool.
How Common Are Heel Spurs on X-Rays
Heel spurs are surprisingly common, and plenty of people who have them feel nothing at all. One review of over a thousand consecutive patient X-rays found plantar spurs in about 12% of cases, with women and older patients more likely to have them.6PubMed. The conundrum of calcaneal spurs: do they matter? A larger study looking at age-related changes reported plantar spur rates closer to 32%, with posterior spurs in about 13%. Rates climbed with age, peaking above 40% in people over 70.7PubMed Central. The age dependent change in the incidence of calcaneal spur
The wide range between studies reflects differences in the populations examined, how carefully radiologists looked for small spurs, and what threshold counted as a “spur” versus a normal bony contour. But the broad point is consistent: if you X-rayed every adult’s heel, you’d find spurs in a substantial fraction of them, many of whom have never had heel pain. That’s an important piece of context when you’re staring at your own X-ray trying to figure out whether that white triangle is the source of your problem.
Does the Spur Actually Cause Your Pain
This is one of the most persistent misconceptions about heel spurs. Many people assume the spur itself is stabbing them from the inside, like stepping on a tack embedded in the bone. The reality is more nuanced. A large portion of people with heel spurs have no symptoms whatsoever, and many people with excruciating plantar heel pain have no spur visible on X-ray. The spur is often a bystander, a sign that the area has been under stress, rather than the direct cause of pain.
That said, the relationship isn’t entirely random. In patients who do have plantar fasciitis, spur length and base width correlate with pain severity. One study found that patients whose spurs measured more than 5 mm on the painful side reported significantly higher pain scores than those with smaller spurs.8PubMed Central. Do the presence, size, and shape of plantar calcaneal spurs have any significance in terms of pain and treatment outcomes in patients with plantar fasciitis? Another found that spur length correlated with age, BMI, symptom duration, and overall foot function scores.9PubMed. The association of calcaneal spur length and clinical and functional parameters in plantar fasciitis So bigger spurs tend to go along with worse symptoms and longer-standing disease, even though the spur itself probably isn’t what hurts.
The pain in plantar fasciitis generally comes from the inflamed and thickened plantar fascia, the surrounding soft tissues, and sometimes from bone-level changes that an X-ray doesn’t show well. In one study of over a thousand feet with plantar heel pain, about a quarter had a visible plantar spur and about half had a thickened plantar fascia on imaging, but the two findings frequently overlapped. Roughly one in five feet had both a spur and fascia thickening at the same time.10Rheumatology. Coexistence of plantar calcaneal spurs and plantar fascial thickening in individuals with plantar heel pain That coexistence hints that both are downstream effects of the same mechanical problem rather than one causing the other.
Why the Spur Forms in the First Place
Scientists have debated this for decades, and the honest answer is that the question still isn’t fully settled. Two main theories exist. The traction theory proposes that repeated pulling by the plantar fascia or Achilles tendon on the bone gradually stimulates new bone growth at the attachment site, essentially a slow-motion avulsion. The compression theory argues instead that repetitive ground-impact forces push up against the heel bone, causing tiny stress injuries that trigger a protective bone-building response.
Evidence exists for both sides. One study found that the internal bone structure of spurs doesn’t consistently line up with the pull direction of the fascia, which was initially taken as support for the compression model.11PubMed Central. Plantar calcaneal spurs in older people: longitudinal traction or vertical compression? Separate anatomical work reinforced that the spur’s internal architecture seems to align more with weight-bearing stress than with the direction soft tissues pull.12PubMed. Anatomic relationship of heel spur to surrounding soft tissues: greater variability than previously reported
More recent histological research, however, pushed back. A detailed analysis of both plantar and posterior spurs found that every spur had a clear connection point (enthesis) with either the Achilles tendon or the plantar fascia, and all spurs pointed in the direction of those soft tissues. The researchers concluded that the internal bone pattern was too variable to settle the debate on its own, but the gross orientation of the spurs supported traction as the dominant mechanism.13Scientific Reports. Why heel spurs are traction spurs after all The real answer may involve both processes working together, with chronic stress and repetitive loading triggering bone formation through multiple pathways simultaneously.
When a Heel Spur on X-Ray Suggests an Inflammatory Disease
Most heel spurs are mechanical, meaning they develop from ordinary wear, weight-bearing, and aging. But in some cases, the appearance of a spur on X-ray can raise suspicion for an underlying inflammatory condition, particularly psoriatic arthritis or other forms of spondyloarthritis.
Spurs associated with inflammatory arthritis tend to look different. In psoriatic arthritis specifically, calcaneal spurs are more common than in the general population. One study found that 75% of people with psoriatic arthritis had at least one plantar spur, compared with 47% in the control group. The inflammatory spurs also tended to be broader at the base and longer in the middle segment. Perhaps the most telling radiographic feature was “fluffy plantar periostitis,” an irregular, hazy appearance of new bone forming along the heel surface that was seen in 14% of the psoriatic arthritis group and in none of the controls.14Clinical and Experimental Rheumatology. Radiological characteristics of the calcaneal spurs in psoriatic arthritis
Inflammatory enthesopathy (damage at the tendon-to-bone junction driven by the immune system rather than simple mechanical stress) can also produce erosions, cysts, and aggressive-looking bony overgrowth at the Achilles tendon and plantar fascia attachment sites.15PubMed Central. Diagnostic imaging of psoriatic arthritis. Part I: etiopathogenesis, classifications and radiographic features If your X-ray shows unusually large spurs with fuzzy borders, and especially if they appear on both feet along with joint changes elsewhere, a doctor may investigate further for an autoimmune or inflammatory cause.
What X-Rays Don’t Show Well
Plain X-rays are good at revealing bone, but heel pain often involves soft tissue. The plantar fascia, bursae, fat pad, and Achilles tendon are all structures that contribute to symptoms and that X-rays image poorly. Ultrasound is better at showing fascia thickening, loss of the fascia’s normal layered structure, fluid collections, and increased blood flow that signals active inflammation.16PubMed Central. Imaging of plantar fascia disorders: findings on plain radiography, ultrasound and magnetic resonance imaging Ultrasound is also cheaper, available in many clinics, and doesn’t involve radiation.
MRI goes further still, showing bone marrow edema (fluid-like signal inside the calcaneus) that plain X-rays miss entirely. Bone edema is clinically relevant because patients who have it may respond differently to treatment. In one trial of patients with plantar fasciitis, those whose MRIs showed bone edema had significantly less improvement in pain scores compared to patients without edema.17PubMed Central. The Role of Bone Edema in Plantar Fasciitis Treated with Temperature-Controlled High-Energy Adjustable Multi-Mode Emission Laser (THEAL) and Exercise That kind of detail is invisible on the lateral X-ray where the spur shows up so clearly.
So while a lateral foot X-ray is often the first imaging study ordered for heel pain and is excellent at confirming whether a spur exists, it gives an incomplete picture. A spur-free X-ray doesn’t rule out plantar fasciitis, and a spur-positive X-ray doesn’t confirm it. Clinicians treat the patient and their symptoms, not the X-ray finding in isolation.
Other Angles and X-Ray Measurements
When a radiologist reads a heel X-ray, the spur isn’t the only thing they evaluate. Several angular measurements help characterize the overall shape and biomechanics of the heel bone. The calcaneal inclination angle (the tilt of the calcaneus relative to the ground), for instance, was found to be significantly lower in patients with plantar calcaneal spurs compared to people without them, even though both groups fell within normal limits.18The Journal of Foot and Ankle Surgery. Radiologic and Demographic Characteristics of Patients With Plantar Calcaneal Spur A flatter heel, in other words, seems to go along with spur development, which fits with the biomechanical stress theories of spur formation.
There are also measurements used to assess the heel’s fat pad thickness and the soft tissue layer beneath the fascia. One older but influential study of patients with unilateral heel pain found that the painful side had significantly thicker fat pad and subfascial tissue measurements on X-ray compared to the non-painful side.19SAGE Journals. Painful heel syndrome: radiographic and treatment assessment This is a reminder that even on a simple X-ray, soft-tissue swelling can sometimes be detected if you know where to look.
Heel X-Rays in Children
If a child complains of heel pain and gets an X-ray, the picture looks very different from an adult’s. Children’s heel bones have a growth plate (apophysis) at the back of the calcaneus that hasn’t yet fused. On X-ray, this growth plate normally appears as a separate sliver of bone, which can look alarming to parents who see it and think it’s a fracture or spur. In Sever’s disease, the most common cause of heel pain in active kids, the growth plate may appear denser (more white) and fragmented on X-ray. But some research has shown that these same findings can appear in perfectly healthy children with no pain at all. That makes X-ray interpretation in pediatric heel pain trickier than in adults, and clinicians rely more heavily on the physical exam and symptom history than on imaging alone.
Automated Spur Detection With Artificial Intelligence
A growing area of research involves training AI systems to identify heel bone abnormalities on lateral foot X-rays automatically. One recent study built a dataset of nearly 4,000 annotated lateral X-ray images and used a specialized neural network to detect and classify heel bone diseases. The system achieved accuracy above 94% on new images it hadn’t been trained on, with an area under the curve of about 99%.20International Journal of Imaging Systems and Technology. HeCapsNet: An enhanced capsule network for automated heel disease diagnosis using lateral foot X‐Ray images While this technology isn’t yet standard in clinics, it reflects a broader trend toward using AI as a second reader for musculoskeletal imaging. For high-volume radiology practices, automated spur detection could help ensure small or borderline spurs aren’t overlooked, particularly when the X-ray was ordered for a different reason.
The potential is especially interesting for population screening and research. Manually measuring spur length, base width, and angles across thousands of X-rays is tedious work. If AI can reliably perform those measurements, it opens the door to much larger epidemiological studies that could finally clarify some of the lingering questions about which spur characteristics predict symptoms and which are incidental.