A heel spur, technically known as a calcaneal spur, is a bony projection that develops on the underside of the heel bone, or calcaneus. This growth is composed of calcium deposits and forms slowly over many months or years, often in response to chronic strain and irritation in the foot. It is a common finding, frequently co-occurring with inflammation of the plantar fascia, which is the thick band of tissue running across the bottom of the foot. The presence of a heel spur is typically confirmed through medical imaging, providing a visual confirmation of this bony change in the foot’s structure.
External Appearance of the Foot
The presence of a heel spur on the calcaneus does not usually result in a noticeable lump or protrusion on the skin’s surface. Because the spur is a growth on the bone, it is deep inside the foot and covered by layers of muscle, fat, and skin. The spur itself is generally not visible to the naked eye.
However, the condition that often accompanies a heel spur, plantar fasciitis, can sometimes cause subtle visual changes. Inflammation of the surrounding soft tissues may lead to mild, generalized puffiness or edema around the heel. In rare instances, a posterior heel spur, which forms on the back of the heel where the Achilles tendon attaches, may be large enough to cause a visible bump under the skin.
Internal Appearance on Imaging
A heel spur is most clearly seen on a lateral view X-ray of the foot, appearing as a dense, white projection because of its bony composition. The spur originates from the bottom front of the calcaneus, extending forward toward the ball of the foot. Its shape can vary significantly, sometimes looking like a small hook, a sharp spike, or a broader shelf of bone.
The size of the bony outgrowth is also variable, ranging from tiny, only a few millimeters, to a more substantial half-inch or more in length. Regardless of the exact shape, the structure is a distinct, abnormal calcification on the heel bone’s surface. On the X-ray, the spur is a stark contrast to the surrounding soft tissues, which are not visible in the same detail. Detecting the spur on imaging is a definitive way to diagnose this specific anatomical change.
The Formation Process
The development of the spur begins with repetitive and excessive strain on the tendons and ligaments of the foot that attach to the heel bone, particularly the plantar fascia. This chronic pulling and stretching create repeated micro-tears and localized inflammation at the insertion point of the plantar fascia and the small intrinsic foot muscles on the calcaneus. The body attempts to repair this site of repeated injury through a biological process that involves depositing calcium.
Over many months, this constant repair cycle leads to the accumulation of calcium deposits on the surface of the bone. This mineral accumulation gradually hardens, a process known as calcification, forming the bony projection seen on the X-ray. The resulting heel spur is essentially a localized bone growth that the body created as a protective response to stabilize the area under persistent stress.
The common association with plantar fasciitis is explained by the spur forming directly in response to the chronic inflammation and tension in the plantar fascia tissue. The spur is the hardened, calcified result of the body’s reaction to the soft tissue injury. While the spur is the visible bony change on the X-ray, the soft tissue inflammation of the plantar fascia is often the true source of any resulting heel pain.