Osteoarthritis is a joint disease in which the protective cartilage covering the ends of your bones gradually breaks down, eventually causing pain, stiffness, and loss of movement. It affects roughly 607 million people worldwide and is the single most common form of arthritis. In the United States alone, about 33 million adults have been diagnosed with it. Despite its reputation as simple “wear and tear,” osteoarthritis involves complex changes to every tissue inside the joint, not just cartilage.
What Happens Inside the Joint
Healthy cartilage is smooth, slippery, and acts as a shock absorber between bones. In osteoarthritis, that cartilage loses its structure in stages. Early on, the tissue softens and develops tiny surface cracks. It holds more water than normal while losing the proteins that give it strength and bounce. The cells responsible for maintaining cartilage begin to die off faster than they can be replaced. Over time, the cartilage thins, develops deeper fissures, and can wear away entirely, leaving raw bone exposed.
But the damage doesn’t stop at cartilage. The bone just beneath it responds by thickening and forming bony spurs (called osteophytes) along the joint margins. Paradoxically, this extra bone is structurally weaker than normal bone because its mineral content is abnormal. Lesions can also appear in the bone marrow, consisting of swelling, dead tissue, and scarring.
The soft tissue lining the joint, called the synovium, gets involved too. It thickens, develops new blood vessels, and releases inflammatory chemicals that speed up cartilage destruction. This inflammation is why osteoarthritis can cause swelling and warmth around the joint, symptoms many people associate only with other forms of arthritis.
Which Joints Are Most Affected
Osteoarthritis most commonly strikes the knees, hips, hands, and spine. Each location produces its own pattern of symptoms:
- Knees: You may hear a grinding or scraping noise when walking or bending. Stiffness after sitting is common, and pain tends to worsen with stairs or prolonged standing.
- Hips: Pain often shows up in the groin, inner thigh, or buttocks rather than on the outside of the hip. It can radiate down to the knee, which sometimes leads people to think the knee itself is the problem.
- Hands: Bony enlargements develop at the finger joints over time, changing their shape and sometimes limiting grip strength.
- Spine: Stiffness and pain concentrate in the neck or lower back, and bone spurs can occasionally press on nearby nerves.
What Osteoarthritis Feels Like
The hallmark is pain that worsens with activity and improves with rest, at least in the earlier stages. You might notice your joints feel stiff first thing in the morning or after sitting for a while, but this stiffness typically loosens up within about 30 minutes. That short duration is one of the features that distinguishes osteoarthritis from inflammatory types of arthritis, where morning stiffness can last an hour or more.
As the disease progresses, pain can become more persistent. Some people feel it even at rest or during the night. The joint may lose range of motion gradually, making everyday tasks like climbing stairs, opening jars, or bending down more difficult. Swelling around the joint is common during flare-ups, and you might feel or hear crackling and popping when you move.
How It Differs From Rheumatoid Arthritis
People often confuse osteoarthritis with rheumatoid arthritis, but they are fundamentally different diseases. Rheumatoid arthritis is an autoimmune condition in which the immune system attacks the joint lining. It most commonly begins between ages 40 and 60 and tends to affect joints symmetrically (both wrists at once, for example). Osteoarthritis is driven primarily by mechanical and biological breakdown, and its prevalence rises more steeply in older age. It can affect just one knee or one hip without necessarily involving the same joint on the other side.
Both conditions involve inflammation, but in rheumatoid arthritis the inflammation is the root cause, while in osteoarthritis it is more of a secondary response that accelerates damage already underway. Blood markers of systemic inflammation tend to be more dramatically elevated in rheumatoid arthritis, and treatment strategies differ significantly because of this.
Major Risk Factors
Age is the strongest predictor. Cartilage simply accumulates damage over decades, and the body’s repair mechanisms slow down. But several other factors increase your risk well beyond what age alone would explain.
Body weight is one of the most important. Every pound of body weight translates to roughly three to six pounds of force on the knee with each step, so being just 10 pounds overweight adds 30 to 60 pounds of extra load per stride. People in the heaviest weight category have up to 10 times the risk of knee osteoarthritis compared to those in the lightest. In the well-known Framingham study, women of normal height who lost about 11 pounds cut their risk of developing knee osteoarthritis by more than 50 percent. Interestingly, being overweight is also linked to higher rates of hand osteoarthritis, suggesting that excess body fat contributes through inflammatory chemicals circulating in the blood, not just mechanical stress.
Previous joint injuries, even those that healed well, significantly raise the odds of osteoarthritis developing in that joint years or decades later. Jobs or sports that involve repetitive heavy loading on specific joints also contribute over time. Women are affected more often than men, particularly after menopause, and genetics play a role in how resilient your cartilage is to begin with.
How Severity Is Measured
Doctors typically gauge osteoarthritis severity using X-rays, grading what they see on a scale from 0 to 4. At grade 0, the joint looks normal. Grade 1 shows possible tiny bone spurs but no clear cartilage loss. By grade 2, bone spurs are definite and cartilage may be starting to thin. Grade 3 shows obvious cartilage narrowing, some bone hardening, and possible changes in bone shape. Grade 4 is the most advanced: large bone spurs, severe cartilage loss, dense bone hardening, and visible deformity of the bone ends.
One important thing to understand is that X-ray severity doesn’t always match how much pain you feel. Some people with grade 2 changes have significant daily pain, while others with grade 3 or 4 changes manage relatively well. This disconnect is partly because pain in osteoarthritis comes from multiple sources: the bone, the inflamed joint lining, stretched ligaments, and sensitized nerves, not just cartilage loss alone.
Managing Osteoarthritis Day to Day
There is no way to reverse cartilage loss once it has occurred, but the disease progresses at very different rates in different people, and several strategies can slow that progression and reduce pain. Regular low-impact exercise, such as swimming, cycling, or walking, strengthens the muscles that support the joint, which reduces the load on damaged cartilage. Strength training around the affected joint is one of the most consistently effective interventions for both pain and function.
Weight management makes a measurable difference, especially for knee and hip osteoarthritis. Even modest weight loss reduces joint stress and lowers circulating inflammatory markers. Physical therapy can help you learn movement patterns that protect vulnerable joints, and assistive devices like braces or supportive footwear redistribute mechanical forces.
For pain relief, over-the-counter anti-inflammatory medications and topical treatments applied directly to the joint are common first steps. Joint injections can offer temporary relief when oral options are not enough. When cartilage is severely destroyed and pain significantly limits daily life, joint replacement surgery has high success rates, particularly for hips and knees, with most people returning to normal activities within a few months.