Knee arthritis typically shows up as pain during or after movement, stiffness that’s worst when you first get up, and a gradual loss of the knee’s full bending or straightening ability. Unlike a sudden injury, these symptoms build slowly over weeks to months and tend to affect both activity and rest in predictable patterns. Understanding what to look for can help you figure out whether arthritis is the likely cause of your knee trouble.
The Most Common Symptoms
Osteoarthritis is by far the most common type of arthritis in the knee, and its hallmark is pain that gets worse with use. You might notice it climbing stairs, getting up from a chair, or walking longer distances. The pain often eases with rest early on, but as the condition progresses, it can linger even when you’re sitting still. Some people describe a deep ache inside the joint, while others feel sharper pain along the inner or outer side of the knee.
Beyond pain, there are several other signs to watch for:
- Stiffness after rest. Your knee feels tight or locked up when you wake up or after sitting for a while. With osteoarthritis, this typically lasts about 10 to 15 minutes and loosens as you move around.
- Grinding or crackling. You may feel a grating sensation when bending or straightening the knee, sometimes with an audible pop or crackle. This happens when the smooth cartilage cushioning the joint has worn down.
- Swelling. The knee may look puffy or feel warm, caused by soft tissue inflammation around the joint.
- Tenderness. Pressing gently on or around the kneecap produces discomfort.
- Loss of range. You can’t fully straighten your leg or bend it as far as you used to. In clinical terms, losing even 5 degrees of full extension or being unable to bend past about 110 degrees points toward arthritis changes in the joint.
- Hard lumps near the joint. Bone spurs, which are extra bits of bone that form as the body tries to stabilize a damaged joint, can sometimes be felt as firm bumps around the knee.
Not everyone has all of these at once. Early arthritis might show up as nothing more than an aching knee after a long walk that goes away by the next morning. Over time, the symptoms become more persistent and affect more daily activities.
How Morning Stiffness Helps Tell the Type
The duration of your morning stiffness is one of the simplest clues for distinguishing osteoarthritis from rheumatoid arthritis. With osteoarthritis, stiffness after waking averages 10 to 15 minutes and fades once you get moving. If your knee stays stiff for more than an hour each morning, that pattern is more consistent with rheumatoid arthritis, an autoimmune condition where the immune system attacks the joint lining.
Rheumatoid arthritis also tends to affect joints symmetrically (both knees, or knees plus hands and feet) and causes more pronounced warmth and swelling. Osteoarthritis can certainly affect both knees, but it often starts in one knee or is noticeably worse on one side, particularly if that knee has a history of injury.
Who Gets Knee Arthritis
Certain factors make knee arthritis significantly more likely. Research looking at prediction models for knee osteoarthritis found that body weight is one of the strongest modifiable risk factors: each standard deviation increase in BMI raised the odds of developing knee arthritis by about 28%. Extra weight doesn’t just increase the load on your knees. It also promotes low-grade inflammation throughout the body that accelerates cartilage breakdown.
Gender plays a role too. Women are roughly 1.6 times more likely than men to develop knee osteoarthritis, a gap that widens after menopause. Age is the other major driver. Cartilage loses its ability to repair itself over time, making arthritis increasingly common from your 50s onward. Previous knee injuries, including ligament tears, meniscus damage, or fractures involving the joint surface, substantially raise your risk even decades later. If you tore your ACL playing sports in your 20s, that knee is a prime candidate for arthritis in your 40s or 50s. Having arthritis in your hands also correlates with a higher chance of developing it in the knee, suggesting a shared genetic or metabolic component.
Arthritis vs. a Meniscus Tear
This distinction matters because treatment paths are different, and the two conditions frequently overlap. A meniscus tear usually starts with a specific incident: you twisted your knee, felt a pop, and the pain was immediate. Arthritis pain creeps in gradually without a clear triggering event.
The most telling difference is mechanical symptoms. If your knee catches, locks, or gives way suddenly, that usually points to a loose flap of torn cartilage or a free fragment floating in the joint. Arthritis causes stiffness and restricted motion, but the knee doesn’t typically lock in place the way it does with a meniscus tear. Pain location can be similar for both conditions, often felt along the inner or outer joint line, which is why imaging is usually needed to sort them out. In people who already have some arthritis, a new meniscus tear on top of it can be especially hard to identify by symptoms alone.
What Happens at the Doctor’s Office
A doctor can often diagnose knee arthritis through a physical exam and your symptom history alone. They’ll bend and straighten your knee to check range of motion, feel for warmth and swelling, and press around the joint to locate tenderness. One common test involves gently pushing fluid from one side of the knee to the other. If the tissue on the opposite side bulges outward, it confirms there’s excess fluid in the joint, a sign of active inflammation.
X-rays are the standard imaging tool. They show narrowing of the space between the bones (where cartilage has worn away), bone spurs along the joint edges, and changes to the bone surface. A normal X-ray doesn’t completely rule out early arthritis, since cartilage damage can exist before it shows up on film, but visible joint space narrowing is strong confirmation.
MRI scans aren’t routinely needed for a straightforward arthritis diagnosis, but they’re useful when your doctor suspects a meniscus tear, ligament injury, or other soft tissue problem alongside or instead of arthritis.
Blood Tests and What They Can (and Can’t) Tell You
There’s no blood test that diagnoses osteoarthritis. Blood work is primarily used to check for inflammatory types of arthritis, like rheumatoid arthritis. If your doctor suspects an inflammatory cause, they may test for rheumatoid factor and anti-CCP antibodies, which are immune markers that help confirm rheumatoid arthritis when the clinical picture fits.
One important nuance: these tests aren’t useful as screening tools for general joint pain. Rheumatoid factor can show up positive in older adults and people with other conditions who don’t have rheumatoid arthritis at all. Routine testing of everyone with knee pain leads to misleading false positives. These blood markers are most informative when there’s already clinical evidence of inflammatory joint disease, like prolonged morning stiffness, significant swelling in multiple joints, or symmetrical involvement.
Signs That Point Toward Arthritis Rather Than Something Else
Putting it all together, the pattern that most strongly suggests knee arthritis includes pain that worsens with activity and improves with rest, brief morning stiffness that resolves within 15 to 20 minutes, gradual onset over months rather than sudden injury, crackling or grinding in the joint, and mild to moderate swelling that comes and goes. If you’re over 50, carry extra weight, or have a history of knee injury, the probability goes up considerably.
Symptoms that suggest something other than osteoarthritis include severe swelling and redness that develops quickly (which could signal gout, infection, or an autoimmune flare), morning stiffness lasting well over an hour, locking or catching in the joint, and pain that started abruptly after a specific twist or impact. These don’t rule out arthritis entirely, but they warrant a more thorough workup to check for other or additional diagnoses.