Osteoarthritis is the most common form of arthritis by a wide margin. Of the roughly 67 million U.S. adults diagnosed with some form of arthritis, about 33 million have osteoarthritis, accounting for nearly half of all cases. The next most common type, rheumatoid arthritis, affects around 10.6 million. Understanding what sets osteoarthritis apart, what causes it, and how to manage it can make a real difference in how it affects your daily life.
What Osteoarthritis Actually Is
Osteoarthritis is a disease of joint breakdown. It centers on cartilage, the firm, slippery tissue that cushions the ends of your bones where they meet. In a healthy joint, cartilage lets bones glide past each other smoothly. In osteoarthritis, that cartilage gradually deteriorates in a predictable sequence.
First, enzymes in the joint begin breaking down the proteins that give cartilage its structure and resilience. The cartilage surface starts to fray and erode, and fragments of broken-down tissue float into the fluid surrounding the joint. Those fragments trigger inflammation: the joint lining absorbs them and responds by releasing inflammatory signals that speed up further cartilage destruction. This creates a cycle where damage feeds more damage.
At the same time, the inflammatory signals suppress the cartilage cells’ ability to repair themselves. They reduce production of the very proteins the cartilage needs to stay intact while ramping up the enzymes that tear it apart. Over time, the cartilage thins unevenly, bone underneath it thickens and hardens, and small bony growths called bone spurs form around the joint edges. The result is a joint that’s stiffer, more painful, and less able to move through its full range.
Where It Typically Shows Up
Osteoarthritis most often affects the knees, hips, hands, fingers, and spine. Unlike rheumatoid arthritis, which tends to strike the same joint on both sides of the body simultaneously, osteoarthritis usually starts in a single joint or is noticeably worse on one side. It’s common for someone to have significant pain in one knee, for example, while the other feels relatively fine.
Morning stiffness is a hallmark of both osteoarthritis and rheumatoid arthritis, but the duration is a useful distinguishing feature. In osteoarthritis, morning stiffness typically improves in under 30 minutes. If stiffness lasts longer than that, it points more toward rheumatoid arthritis or another inflammatory type.
How It Differs From Rheumatoid Arthritis
Rheumatoid arthritis is an autoimmune disease, meaning the immune system mistakenly attacks the body’s own joint tissue. Osteoarthritis is not autoimmune. It’s driven by mechanical wear and the enzymatic breakdown described above. This distinction matters because the two conditions behave differently and are managed differently.
Rheumatoid arthritis often comes with systemic symptoms early on: fatigue, low-grade fever, anemia, and loss of appetite. It can also affect organs beyond the joints, including the heart, eyes, and lungs. Osteoarthritis is primarily a joint-level problem. You feel it where the cartilage is wearing down, but it doesn’t cause the widespread body-wide inflammation that rheumatoid arthritis does.
The symmetry pattern is another key difference. Rheumatoid arthritis typically appears in matching joints on both sides, often starting in smaller joints like the hands and feet. Osteoarthritis tends to develop in weight-bearing joints or joints with a history of injury, and it’s usually asymmetric.
Who Is Most at Risk
Age is the strongest predictor. As you get older, the cumulative wear on joints adds up, muscle mass declines (reducing joint stability), and the body’s ability to repair cartilage slows. But age alone doesn’t make osteoarthritis inevitable. Several other factors raise or lower your risk significantly.
Women develop osteoarthritis more often than men. Carrying extra weight is one of the most impactful modifiable risk factors, particularly for knee osteoarthritis. Excess body weight doesn’t just add load to the joint; every extra pound translates to roughly three to four pounds of additional pressure on your knees with each step. Losing just ten pounds removes about 40 pounds of force from your knee joints.
Joint injuries are a major contributor. An ACL tear in your twenties, for example, significantly raises your odds of developing osteoarthritis in that same knee years or decades later. Occupations that involve repetitive bending, squatting, or kneeling also increase risk. Military veterans have higher arthritis rates, likely tied to the physical demands and injuries common during service.
How It’s Diagnosed
Diagnosis starts with your symptoms and a physical exam. Your doctor will ask about the pattern of pain and stiffness, which joints are affected, and how your symptoms change throughout the day. When the diagnosis isn’t clear from the exam alone, X-rays can help confirm it.
On an X-ray, osteoarthritis has a recognizable signature: uneven narrowing of the joint space (where cartilage has worn thin), hardening of the bone just below the cartilage surface, and small bony spurs at the joint margins. In more advanced cases, small cysts can form within the bone near the joint. These findings, combined with the clinical picture, are usually enough to distinguish osteoarthritis from other types of arthritis without needing blood tests or more advanced imaging.
Managing Pain and Staying Active
There’s no way to reverse cartilage loss once it’s happened, but the right approach can meaningfully reduce pain and slow progression. Physical activity is one of the most effective tools available, even though moving a painful joint might feel counterintuitive.
The general recommendation is at least 150 minutes per week of moderate-intensity aerobic activity, plus muscle-strengthening exercises on at least two days per week. You don’t need to do it all at once. Sessions as short as five or ten minutes count and add up over the course of a week. Stronger muscles around a joint absorb more of the forces that would otherwise stress the cartilage, which is why strength training matters as much as cardio.
Joint-friendly activities that keep stress on the joints low include brisk walking, cycling, swimming, water exercises, dancing, and tai chi. For strength training, choose weights or resistance bands at a level that doesn’t trigger joint pain. Older adults benefit from adding balance exercises to the mix, since falls can worsen joint damage.
The Role of Weight Management
If you carry extra weight and have knee or hip osteoarthritis, weight loss is one of the single most effective things you can do. The math is striking: because of the mechanics of walking, your knees experience a multiplied version of your body weight with every step. That three-to-four-times multiplier means even modest weight loss produces outsized relief. People who lose weight often report noticeable improvement in pain and mobility before they’ve reached any dramatic number on the scale.
Weight management also appears to slow the progression of joint damage over time, not just manage symptoms. Combined with regular low-impact exercise, it forms the foundation of osteoarthritis management, often reducing the need for pain medication.