Osteoarthritis is the most common form of arthritis, a condition where the protective cartilage that cushions the ends of your bones gradually breaks down, leading to pain, stiffness, and loss of movement. As of 2019, roughly 528 million people worldwide were living with it, a 113% increase since 1990. It most often develops in the late 40s to mid-50s, though younger people with joint injuries can develop it too.
What Happens Inside the Joint
Healthy cartilage is smooth and slippery, allowing bones to glide against each other with minimal friction. In osteoarthritis, the internal structure of that cartilage changes before any visible damage appears. The molecular composition shifts first, and the cartilage cells (which normally have very little ability to repair themselves) attempt a brief burst of activity, multiplying and producing new material to patch things up.
That repair effort fails. As the structural proteins holding cartilage together break down, the cartilage surface cracks and thins. The cells eventually die off, and the cartilage can be lost entirely in advanced cases. Without that cushion, bone grinds against bone. The body responds by thickening the bone underneath the cartilage and growing bony spurs around the joint edges. Muscles and tendons around the joint can weaken over time, compounding the instability.
This process is slow, often unfolding over years or decades. It’s not simply “wear and tear” from aging, though age is a major factor. Active biological processes, including inflammation and abnormal bone remodeling beneath the cartilage surface, drive the disease forward.
Which Joints It Affects Most
The knee is by far the most common location, affecting an estimated 365 million people globally. Hips and hands are the next most frequent sites. Hip osteoarthritis often causes pain not just in the hip itself but also in the groin, inner thigh, buttocks, or even the knee, which can make it tricky to pinpoint. The spine (particularly the neck and lower back) is another common area. About 73% of people living with osteoarthritis are over 55, and 60% are female.
Common Symptoms
The hallmark symptoms are joint pain that worsens with activity and improves with rest, along with stiffness that typically lasts less than 30 minutes after waking up or sitting for a while. That short duration of morning stiffness is one of the features that distinguishes osteoarthritis from inflammatory types of arthritis, where stiffness can persist for an hour or more.
Other signs include:
- Swelling around the joint, especially after prolonged use
- A grinding or scraping sensation during movement
- Gradual loss of range of motion
- Knee buckling due to weakened muscles and ligaments around the joint
In later stages, pain can become constant and may worsen at night. It can also spread beyond the joint itself, becoming more diffuse and harder to localize.
How It Differs From Rheumatoid Arthritis
Osteoarthritis and rheumatoid arthritis can look similar on the surface, but they work very differently. Rheumatoid arthritis is an autoimmune disease where the immune system attacks the joint lining, typically affecting joints symmetrically on both sides of the body. Blood tests in rheumatoid arthritis often show significantly elevated inflammatory markers like rheumatoid factor and anti-CCP antibodies. In osteoarthritis, those markers are usually normal or only mildly elevated, though some overlap exists in early cases, which can make diagnosis challenging.
Major Risk Factors
Excess body weight is one of the strongest and most modifiable risk factors, particularly for knee osteoarthritis. Every 5-unit increase in BMI raises the risk of knee osteoarthritis by 35%. People with a BMI above 35 are nearly five times more likely to develop knee osteoarthritis compared to people at a normal weight. The good news is that losing weight produces outsized benefits: every pound lost reduces the load on the knee by roughly four times that amount with each step.
Weight doesn’t just add mechanical stress. Fat tissue actively produces inflammatory signals and metabolic mediators that promote cartilage breakdown throughout the body. This helps explain why obesity also increases the risk of osteoarthritis in non-weight-bearing joints like the hands. Insulin resistance and abnormal cholesterol levels, both common in obesity, further contribute to joint degeneration.
Other significant risk factors include previous joint injury, repetitive occupational stress, genetic predisposition, and female sex (especially after menopause).
How Osteoarthritis Is Diagnosed
Diagnosis typically combines a physical exam with X-rays. Doctors look at how much space remains between the bones in a joint (indicating how much cartilage is left), whether bony spurs have formed, and whether the bone beneath the cartilage has thickened. A widely used grading system classifies severity on a 0 to 4 scale:
- Grade 0: Normal joint, no visible changes
- Grade 1: Minor, questionable changes
- Grade 2: Visible bone spurs with possible early cartilage thinning
- Grade 3: Moderate bone spurs, definite cartilage thinning, some bone thickening
- Grade 4: Large bone spurs, severe cartilage loss, significant bone deformity
An important nuance: what shows up on an X-ray doesn’t always match how much pain you feel. Some people with severe-looking joints have mild symptoms, while others with modest imaging findings have significant pain. Symptoms and functional limitations matter as much as the imaging.
Non-Drug Treatments
There is no cure for osteoarthritis, and no medication has been proven to slow or reverse cartilage loss. Because of this, non-drug approaches remain the foundation of management for hip and knee osteoarthritis. Updated EULAR guidelines from 2023, now backed by the strongest level of research evidence, emphasize exercise, weight management, and education as core treatments.
Regular physical activity strengthens the muscles that support and stabilize your joints, improves flexibility, and can reduce pain over time. Low-impact options like swimming, cycling, and walking are commonly recommended. Strength training for the muscles around the affected joint is particularly beneficial for knee osteoarthritis. Physical therapy can help you learn movement patterns that reduce joint stress.
Pain Medication Options
Anti-inflammatory medications, both topical (applied to the skin) and oral (taken by mouth), are the most common pharmacological treatment. A large meta-analysis found that topical and oral versions provide essentially equal pain relief and equal improvement in stiffness and physical function. The difference lies in side effects: oral anti-inflammatories cause significantly more stomach and digestive problems, while topical versions cause about five times more skin reactions like rashes or irritation at the application site.
For osteoarthritis in accessible joints like the knee or hand, topical anti-inflammatories offer a way to get the same pain relief with less risk to your stomach. For deeper joints like the hip, oral options or other approaches may be more practical since topical medications have a harder time penetrating to the joint.
Injection Therapies
Platelet-rich plasma (PRP) injections, which use concentrated components from your own blood, have shown promising results for knee osteoarthritis. A 2025 meta-analysis of 28 trials involving over 3,200 patients found that PRP provided pain relief comparable to hyaluronic acid injections but with better functional improvement, especially when the two were combined. PRP also outperformed physical therapy alone for both pain and function. The best outcomes were seen in people with early-stage disease (grades 1 and 2), reinforcing that earlier intervention tends to yield better results.
When Joint Replacement Becomes an Option
Joint replacement surgery is reserved for cases where conservative treatments have been thoroughly tried and haven’t provided adequate relief. Both EULAR and the U.S. National Institutes of Health consider joint replacement appropriate when X-rays confirm osteoarthritis and the person has continuous pain that medications can’t control, or substantial limitations in daily function.
The decision isn’t based on X-ray findings alone. If imaging shows severe osteoarthritis but you’re managing well with minimal symptoms, surgery isn’t recommended. Conversely, the degree of suffering and its impact on your daily life play a substantial role. Joint replacement is a quality-of-life decision, made when the disease has significantly eroded your ability to do the things that matter to you, and nothing else has helped enough.