Bone spurs form when your body lays down extra bone tissue in response to prolonged pressure, friction, or inflammation at a joint or attachment point. The process unfolds over months or years as specialized bone cells detect mechanical stress and gradually deposit calcium to reinforce the area. Nearly everyone develops at least small bone spurs with age: one ultrasound study of over 400 factory workers found detectable spurs in 99.8% of participants at finger joints alone, with most people completely unaware of them.
The Basic Mechanism: Stress Triggers New Bone
Your skeleton is not a fixed structure. Bone tissue constantly breaks down and rebuilds itself based on the forces it experiences, a principle known as Wolff’s Law. Cells embedded in your bones act as sensors, detecting local mechanical cues like compression, tension, and vibration. When a particular spot absorbs repeated force, these cells recruit bone-building cells to reinforce the area with new tissue. This is the same process that makes a marathon runner’s leg bones denser over time. But when the stress is concentrated at a joint edge, tendon attachment, or disc margin, the reinforcement doesn’t just thicken existing bone. It extends outward as a small projection, or spur.
The technical name for a bone spur is an osteophyte. Most start as tiny, smooth bumps that never cause problems. Over time, if the underlying stress continues, they can enlarge enough to press against soft tissue, nerves, or other bones.
Cartilage Loss and Joint Spurs
Joint damage from osteoarthritis is the single most common cause of bone spurs. The sequence works like this: cartilage, the smooth cushion between bones in a joint, begins to wear thin. As it degrades, the underlying bone absorbs more impact with each movement. Your body interprets this as a signal that the joint needs more structural support. In response, bone-building cells activate along the joint margins and begin constructing new bone outward.
Research in mouse models has shown that accumulated mechanical stress on cartilage cells triggers them to shift into a state called hypertrophy, where they enlarge and begin behaving more like bone-precursor cells. Essentially, the cartilage cells at the joint edges start participating in a bone-formation process that normally only happens during skeletal growth. This is one reason bone spurs so reliably accompany arthritis: the same stress that destroys cartilage simultaneously kick-starts spur growth at the joint’s borders.
This process is most visible in weight-bearing joints like the knees and hips, but it also affects the hands, especially at the finger joints closest to the nails and the base of the thumb.
How Heel Spurs Develop
Heel spurs follow a slightly different path. Rather than forming at a joint surface, they grow where a ligament or tendon anchors into bone. The most common scenario involves the plantar fascia, the thick band of tissue running along the bottom of your foot. When this tissue becomes chronically inflamed (plantar fasciitis), it tugs repeatedly at its attachment point on the heel bone. Your body responds to that stress by depositing calcium at the attachment site, and over time this deposit hardens into a bony spike that can extend up to half an inch forward along the sole.
You can also develop heel spurs from repeatedly tearing the membrane that lines the heel bone, or from gait abnormalities that shift pressure unevenly across the foot. The spur itself often isn’t the source of pain. It’s the inflamed soft tissue around it that hurts, which is why many people with visible heel spurs on X-rays have no symptoms at all.
Spinal Bone Spurs
In the spine, bone spurs form on vertebral bodies, facet joints (the small connecting joints between vertebrae), and along the edges of intervertebral discs. The trigger is the same: disc degeneration or facet joint arthritis increases bone-on-bone contact, and the body reinforces those margins with new growth.
Spinal bone spurs become a problem when they grow into tight spaces. The spinal canal and the small openings where nerve roots exit the spine don’t have much room to spare. As spurs enlarge, they can press against spinal nerves or nerve roots, causing inflammation, irritation, and compromised nerve function. Depending on where this happens, you might feel pain, numbness, or tingling radiating into an arm or leg. In the neck, spurs can occasionally make swallowing uncomfortable if they project forward toward the throat.
Who Develops Them and When
Age is the strongest predictor. The ultrasound study of factory workers found that osteophyte scores increased by a measurable amount each year of life, and the proportion of joints without any spurs was highest in the youngest participants. No large, advanced-grade spurs were detected in anyone under 31, and women under 51 had none in the most severe category. By middle age, most people have at least small spurs forming somewhere, whether or not they know it.
Beyond age, the risk is higher if you have any form of arthritis. Obesity increases load on weight-bearing joints and accelerates cartilage breakdown. Repetitive occupational movements, running on hard surfaces, wearing unsupportive footwear, and previous joint injuries all concentrate mechanical stress in ways that promote spur growth. Poor posture and spinal alignment issues play a similar role in the neck and back by shifting forces unevenly across vertebral surfaces.
Why Most Bone Spurs Go Unnoticed
The near-universal prevalence of small bone spurs tells you something important: having them is normal, and the vast majority never produce symptoms. A spur only becomes a clinical problem when it grows large enough to physically interfere with a nerve, tendon, or joint’s range of motion. Many people discover bone spurs incidentally on an X-ray taken for an unrelated reason and are surprised to learn they’ve had them for years.
When spurs do cause trouble, the symptoms depend entirely on location. A spur in the knee might limit how far you can bend or straighten the joint. One in the shoulder can catch on the rotator cuff tendons during overhead movements. Spinal spurs may cause nerve-related symptoms like radiating pain or numbness that come and go depending on posture and activity. In each case, it’s the interaction between the spur and surrounding soft tissue that produces symptoms, not the spur in isolation. That distinction matters because treatments often focus on reducing inflammation and improving mobility rather than removing the spur itself.