A heel spur is a bony protrusion, or calcium deposit, that forms on the underside of the heel bone, which is medically known as the calcaneus. This formation develops over a long period, often in response to chronic strain on the foot’s structures. While not all heel spurs cause discomfort, they are frequently discovered in people experiencing heel pain. This bony growth can extend forward toward the arch of the foot, which is why it is also known as a plantar calcaneal spur.
The Exact Anatomical Location
The heel spur is located on the inferior, or bottom, surface of the calcaneus, the largest bone in the foot. Specifically, the spur forms near the medial tuberosity of the heel bone, the area that makes contact with the ground when you walk. This bony growth extends forward toward the arch, sometimes reaching up to half an inch in length.
This location is significant because it is the attachment site for the plantar fascia, a thick band of tissue running along the sole of the foot, and several small intrinsic foot muscles. While the term “heel spur” usually refers to this inferior growth, a less common type can form on the posterior aspect (the back of the heel) where the Achilles tendon attaches. The inferior calcaneal spur is the type most commonly associated with heel pain.
How the Spur Develops
The formation of a heel spur is a biological response to long-term mechanical stress and irritation at the attachment points on the heel bone. When the plantar fascia or foot muscles are repeatedly strained, they pull on the periosteum, which is the thin layer of tissue covering the bone. This persistent pulling creates micro-trauma at the bone’s surface.
In an attempt to stabilize the irritated area, the body begins a gradual process of depositing calcium. Over months or years, this accumulation of calcium deposits hardens into the bony projection known as a heel spur. This process is often a secondary result of chronic plantar fasciitis, which involves inflammation of the plantar fascia.
The pain people feel in their heel is typically caused by the inflammation of surrounding soft tissues, such as the plantar fascia, and not the spur itself. The spur can exist without causing pain and is often an incidental finding on X-rays taken for other reasons. Soft tissue inflammation is the source of sharp, stabbing heel pain.
Visualizing the Spur
Because the heel spur is a bony structure deep within the foot, it cannot be felt or seen simply by looking at the foot from the outside. Confirming the presence and exact location of a heel spur requires medical imaging. The primary tool used for this purpose is a simple X-ray, which is highly effective at visualizing bone.
The X-ray will clearly show the bony outgrowth projecting from the calcaneus, allowing a healthcare professional to distinguish it from other causes of heel pain. The size of the heel spur visible on the X-ray often has a poor correlation with the amount of pain a person experiences. A small spur can be associated with intense pain due to significant soft tissue inflammation, while a large spur may be completely asymptomatic.