Bone spurs form when the body deposits extra bone along the edges of existing bones, usually at joints. The most common trigger is joint damage from osteoarthritis, where the body attempts to repair worn-down cartilage by growing new bone near the damaged area. But osteoarthritis isn’t the only cause. Mechanical stress, metabolic conditions, and simple aging all play a role.
How Bone Spurs Actually Form
A bone spur doesn’t appear overnight. The process begins when stem cells in the tissue surrounding a joint (the periosteum and the joint lining) are activated by damage or stress. These cells first build a small scaffold of cartilage at the edge of the bone. Over weeks to months, the body gradually replaces that cartilage scaffold with hardened bone containing its own internal marrow cavities. The result is a bony projection, sometimes smooth and sometimes jagged, that extends from the original bone surface.
This process mirrors how bones grow during development. The same types of progenitor cells involved in forming joints during embryonic growth are the ones that build osteophytes in adulthood. Meanwhile, a separate population of cells from the joint’s inner lining contributes a cap of cartilage over the spur but doesn’t participate in forming the bone itself. In other words, multiple cell types coordinate to build a spur, and the process is more organized than random bone “growth” might suggest.
Osteoarthritis Is the Leading Cause
Osteoarthritis breaks down the cartilage cushioning the ends of bones inside a joint. As that cushion thins and roughens, the underlying bone experiences more direct pressure and friction than it was designed to handle. The body responds by reinforcing the joint’s edges with extra bone, essentially trying to stabilize a structure that’s losing its shock absorber. This compensatory growth is why bone spurs are so closely linked to arthritis and why they tend to appear at the same joints where cartilage loss is most advanced: knees, hips, fingers, and the spine.
The relationship between cartilage loss and spur formation is so consistent that doctors often use the presence of bone spurs on an X-ray as one indicator of osteoarthritis progression, even before symptoms become severe.
Mechanical Stress and Repetitive Strain
Joints and bones don’t need arthritis to develop spurs. Repeated mechanical stress on tendons and ligaments where they attach to bone can trigger the same repair process. The heel is a classic example. Chronic strain on the plantar fascia (the thick band running along the sole of the foot) pulls repeatedly at its attachment point on the heel bone. Over time, the repeated tearing of the membrane covering the bone stimulates new bone growth at that spot, producing a calcaneal spur.
Heel spurs become significantly more common with age. Among people aged 61 to 70, about 36% have a plantar heel spur visible on imaging. In those over 70, the rate rises to nearly 42%. Posterior heel spurs, which form at the back of the heel where the Achilles tendon attaches, follow a similar pattern, appearing in roughly 20 to 22% of people in those age groups.
The same principle applies anywhere tendons or ligaments meet bone under repetitive load: shoulders, elbows, and the spine are all common sites. Athletes, manual laborers, and anyone whose daily activities place sustained or repeated force on specific joints face higher risk.
Spinal Bone Spurs and Nerve Compression
The spine is one of the most consequential places a bone spur can form, because the spinal canal doesn’t have much room to spare. Spurs can grow from the vertebral body edges, the facet joints at the back of the spine, or around the openings where nerve roots exit the spinal column.
When spurs project into the central spinal canal, they contribute to a condition called spinal stenosis, where the space around the spinal cord narrows. When they grow into the lateral recesses or the foramina (the side tunnels where individual nerves exit), they can press directly on nerve roots. This compression is what causes radiating pain into the arms or legs, numbness, tingling, or weakness, depending on which nerve is affected. The spur itself isn’t painful. The symptoms come from the pressure it places on nearby soft tissue.
Spinal spurs often develop alongside other age-related changes: bulging discs, thickened ligaments, and cartilage loss in the facet joints. These factors combine to narrow the available space, which is why spinal stenosis symptoms tend to worsen gradually over years rather than appearing suddenly.
Metabolic and Systemic Conditions
Some people develop widespread bone spurring driven not by local joint damage but by metabolic factors throughout the body. Diffuse idiopathic skeletal hyperostosis (DISH) is the most notable example. In DISH, large flowing bone formations develop along the spine, sometimes bridging four or more consecutive vertebrae. It can also affect the shoulders, elbows, knees, and heels.
The exact cause of DISH isn’t fully understood, but it’s strongly associated with metabolic disorders: diabetes, insulin resistance, obesity, high cholesterol, and elevated uric acid levels. These conditions appear to shift the body’s bone-building activity into overdrive, particularly along the ligaments and tendons of the spine. DISH is distinct from osteoarthritis because the disc spaces between vertebrae typically remain preserved, and the condition differs from ankylosing spondylitis because the sacroiliac joints aren’t fused.
DISH tends to appear in people over 50 and is more common in men. It can be mild and incidental, or it can cause significant stiffness and, in the cervical spine, occasionally difficulty swallowing when large anterior spurs form near the esophagus.
Age as a Risk Factor
Age is the single strongest predictor of bone spur formation. A high-resolution ultrasound study of factory workers (average age 53) found that 99.8% of participants had at least one small bone spur detectable on their finger joints. Virtually everyone develops some degree of bony outgrowth at joint margins as they age. The researchers concluded that small, grade 1 osteophytes should be considered a normal finding, not a sign of disease.
Larger spurs are less common and more closely tied to actual osteoarthritis. The distinction matters: a small spur visible on imaging doesn’t mean you have a problem. The size, location, and whether the spur is pressing on something sensitive determines whether it will ever cause symptoms. Many people live their entire lives with bone spurs they never feel.
How Quickly Bone Spurs Develop
The timeline varies depending on the type and location. In the spine, MRI tracking of patients with DISH has shown that a large bridging osteophyte can form between two vertebrae within a single year, even at a level that was previously uninvolved, in someone who already had spurs at adjacent levels. This suggests that once the biological conditions are right, new spurs can develop relatively quickly.
For joint-related spurs driven by osteoarthritis, the process is generally slower and tracks with the pace of cartilage loss, which unfolds over years to decades. A spur triggered by repetitive tendon strain, like a heel spur, typically develops over months of sustained activity before it becomes large enough to see on an X-ray. In all cases, the spur itself grows through the same cartilage-to-bone conversion process, but the speed depends on how aggressively the underlying trigger is stimulating new bone formation.
Why Some Bone Spurs Cause Pain and Others Don’t
Bone has no pain receptors on its outer surface in the way skin does. A bone spur causes symptoms only when it physically encroaches on something sensitive: a nerve, a tendon, or the soft tissue lining of a joint. A spur on the top of a finger joint might be visible and cosmetically noticeable but completely painless. The same-sized spur inside the spinal canal might cause debilitating leg pain because it’s pressing on a nerve root.
Location also determines what kind of symptoms to expect. Spurs in the shoulder can limit range of motion by catching on the rotator cuff tendons during overhead movements. Heel spurs may contribute to pain on the sole of the foot with every step. Spinal spurs can cause anything from localized stiffness to radiating nerve pain, depending on exactly where and how large they are. The spur’s size alone is a poor predictor of how much trouble it will cause.