Osteoarthritis is the most common form of arthritis by a wide margin. Out of the roughly 67 million American adults diagnosed with some form of arthritis, about 33.2 million have osteoarthritis, accounting for nearly half of all cases. The next most common type, rheumatoid arthritis, affects about 10.6 million, roughly a third as many people.
What Happens Inside the Joint
Osteoarthritis is fundamentally a problem of cartilage breakdown. Cartilage is the smooth, rubbery tissue that covers the ends of bones where they meet at a joint, allowing them to glide against each other with minimal friction. In osteoarthritis, the cells that maintain this cartilage become overactive in a destructive way. Instead of quietly repairing and maintaining the tissue, they start producing enzymes that break down the cartilage matrix faster than it can be rebuilt.
This process feeds on itself. As cartilage fragments break off, they trigger more inflammation, which stimulates the cells to produce even more destructive enzymes. The inflammation also generates oxidative stress that kills cartilage cells outright. Over time, the cartilage thins and roughens. In advanced stages, bone is exposed and starts rubbing against bone, which is when the condition becomes most painful. The bone underneath can thicken, develop small cysts, and sprout bony growths called osteophytes (bone spurs) at the edges of the joint.
Which Joints It Affects Most
Osteoarthritis most commonly affects the knees, hips, hands, and spine. The knees bear an enormous load during everyday activities like walking and climbing stairs, which makes them especially vulnerable. Hip osteoarthritis can make it increasingly difficult to bend, sit down, or walk comfortably. In the hands, the base of the thumb and the finger joints closest to the fingertips are frequent targets, sometimes producing visible bony nodules. Spinal osteoarthritis typically affects the lower back and neck, where the small facet joints between vertebrae gradually wear down.
How Osteoarthritis Feels
The hallmark symptoms are joint pain and stiffness. The pain is often described as “mechanical,” meaning it gets worse with activity and better with rest. You might notice it most after exercise, when putting weight on the joint, or after repetitive use throughout the day. Early on, resting usually brings relief. As the condition progresses, pain can persist even at rest and may wake you up at night.
Morning stiffness is common but tends to be relatively short-lived, typically lasting 30 minutes or less. If there’s active inflammation in the joint, it can last longer, but it generally improves once you start moving and the joint “warms up.” This is one practical way to distinguish osteoarthritis from rheumatoid arthritis, where morning stiffness often lasts an hour or more.
Other symptoms include a grinding or crackling sensation when you move the joint, reduced range of motion, and occasional swelling. Some people notice that their joints feel looser or less stable over time.
Major Risk Factors
Age is the single biggest risk factor. The cumulative wear on joints over decades, combined with the body’s declining ability to repair cartilage, makes osteoarthritis increasingly common after age 50. But age alone doesn’t explain the full picture.
Excess body weight dramatically raises your risk, especially for knee osteoarthritis. A large cohort study of over 1.7 million people found that obese individuals had more than three times the risk of developing knee osteoarthritis compared to people at a healthy weight. For every five-unit increase in BMI, the risk of knee osteoarthritis rises by about 35%. Interestingly, obesity also increases the risk of hand osteoarthritis, which doesn’t bear any extra load from body weight. This suggests that metabolic factors, not just mechanical stress, play a role.
Those metabolic factors include high blood sugar, insulin resistance, abnormal cholesterol levels, and high blood pressure. Elevated blood sugar, for example, promotes inflammation in joint tissues and accelerates cartilage damage. This cluster of metabolic problems may partly explain why osteoarthritis and cardiovascular disease so often occur together.
Prior joint injuries are another major contributor. A torn ligament, meniscus injury, or fracture involving a joint surface significantly raises the chance of developing osteoarthritis in that joint years or even decades later. Occupations or sports involving repetitive joint stress also increase risk.
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 lining of the joints, causing widespread inflammation. It often starts with flu-like symptoms (fatigue, fever, weakness) before joint pain becomes prominent, and it tends to affect joints symmetrically, both wrists or both knees at the same time.
Osteoarthritis develops gradually over months or years and typically affects joints asymmetrically, at least initially. It doesn’t cause the systemic symptoms that rheumatoid arthritis does. You won’t get fevers or feel generally unwell from osteoarthritis. The pain pattern also differs: osteoarthritis pain worsens with use and improves with rest, while rheumatoid arthritis pain and stiffness are often worst after periods of inactivity and improve with movement. Rheumatoid arthritis can strike at any age, including young adulthood, while osteoarthritis is overwhelmingly a condition of middle and older age.
How It’s Diagnosed
Diagnosis usually starts with a physical exam and a conversation about your symptoms. Your doctor will check for tenderness, swelling, reduced range of motion, and that characteristic grinding sensation during movement. X-rays are the standard imaging tool and can reveal the key signs: narrowing of the space between bones (indicating cartilage loss), bone spurs at the joint margins, and thickening or cysts in the bone just below the cartilage surface.
Doctors use grading systems to classify severity on a scale from 0 to 4. A grade of 0 means no visible signs on X-ray. Grade 2, where definite bone spurs and possible narrowing are visible, is the threshold for a radiographic diagnosis. Grades 3 and 4 represent progressively severe cartilage loss, with grade 4 showing large bone spurs, marked narrowing, and visible bone deformity. It’s worth knowing that X-ray findings don’t always match how much pain someone feels. Some people with significant X-ray changes have mild symptoms, and vice versa.
Treatment and Management
There is no cure for osteoarthritis, but a combination of approaches can significantly reduce pain and keep you functional. The American College of Rheumatology and the Arthritis Foundation strongly recommend exercise as a cornerstone of treatment. This might feel counterintuitive when your joints hurt, but regular physical activity strengthens the muscles that support your joints, improves flexibility, and can reduce pain over time. Low-impact options like walking, swimming, cycling, and tai chi (which has a specific strong recommendation) are particularly well suited.
Weight loss is strongly recommended for anyone with knee or hip osteoarthritis who is overweight or obese. Even modest weight loss can meaningfully reduce the load on weight-bearing joints and lower inflammation throughout the body. Self-management programs that teach you how to handle flare-ups and stay active are also strongly endorsed.
For pain relief, topical anti-inflammatory creams applied directly to the knee are a first-line option with fewer side effects than pills. Oral anti-inflammatory medications are also strongly recommended but carry more risk for the stomach and cardiovascular system with long-term use. Steroid injections into the knee joint can provide temporary relief during flare-ups. Assistive devices like a cane, knee brace, or thumb splint can reduce stress on the affected joint during daily activities.
When the joint is severely damaged and other treatments no longer provide adequate relief, joint replacement surgery, particularly for knees and hips, is highly effective. Most people experience dramatic pain reduction and improved mobility, though recovery takes several weeks to months of rehabilitation.