Bursitis of the knee is inflammation of one or more small, fluid-filled sacs (called bursae) that cushion the bones, tendons, and muscles around your knee joint. These sacs normally reduce friction when you move, but when they become irritated or infected, they swell with excess fluid and cause pain, stiffness, and visible puffiness around the knee. It’s one of the most common causes of knee swelling, especially in people who kneel frequently for work.
Where Knee Bursae Are Located
Your knee has several bursae, but three are most commonly involved in bursitis:
- Prepatellar bursa: Sits directly over the kneecap, just beneath the skin. This is the most frequently inflamed bursa in the knee and the reason bursitis here is sometimes called “housemaid’s knee” or “carpet layer’s knee.”
- Infrapatellar bursae: Two small sacs near the lower part of the kneecap. One lies just beneath the skin over the bony bump at the top of the shinbone, and the other sits deeper, behind the tendon that connects the kneecap to the shin.
- Pes anserine bursa: Located on the inner side of the knee, about 3 to 4 centimeters below the joint line. It cushions the area where three tendons from the inner thigh attach to the shinbone. This type is more common in runners and people with osteoarthritis.
The location of the inflamed bursa determines exactly where you feel pain and swelling, which is why bursitis on the front of the knee feels quite different from bursitis on the inner side.
What Causes It
The most straightforward cause is repeated pressure or friction on the knee. Carpet layers, plumbers, gardeners, and anyone who spends long stretches kneeling on hard surfaces puts direct, sustained pressure on the prepatellar bursa. Over time, this irritation triggers inflammation and fluid buildup.
A direct blow to the knee, such as a fall or a hit during sports, can also set off bursitis by damaging the bursa lining. Overuse injuries from running, jumping, or sudden increases in training volume are a common trigger for pes anserine bursitis specifically. Osteoarthritis and being overweight both increase stress on the inner knee structures and raise the risk of that type as well.
Less commonly, bacteria can enter the bursa through a cut, scrape, or insect bite on the skin over the knee. This is called septic bursitis, and it’s a more serious condition that requires different treatment. The prepatellar bursa is the second most common site of septic bursitis in the body, likely because the skin over the kneecap is thin and frequently exposed to minor injuries.
Septic vs. Non-Infectious Bursitis
This distinction matters because the two types look similar on the surface but require very different approaches. Non-infectious (aseptic) bursitis comes from strain, repetitive pressure, or impact. It’s painful and annoying, but it generally resolves with basic self-care.
Septic bursitis is caused by a bacterial infection inside the bursa. Along with swelling and pain, it often produces warmth, redness that spreads beyond the swollen area, and fever. The skin over the bursa may look taut and shiny. If your doctor suspects septic bursitis, they’ll typically draw fluid from the bursa with a needle and send it to a lab for analysis. Septic bursitis requires antibiotics and sometimes drainage. Left untreated, the infection can spread.
What It Feels Like
The hallmark symptom is a localized, squishy swelling over the affected bursa. With prepatellar bursitis, you’ll notice a soft, puffy area right over your kneecap that can grow to the size of a golf ball or larger. It often looks worse than it feels when you’re sitting still.
Pain typically increases when you kneel, bend the knee fully, or press directly on the swollen area. You may notice stiffness when trying to bend or straighten the knee completely, not because the joint itself is damaged, but because the swollen bursa gets compressed during movement. Walking on flat ground is usually manageable, but stairs and deep bends tend to aggravate it.
With pes anserine bursitis, the tenderness is more focused on the inner side of the knee, slightly below the joint. Pain often flares when climbing stairs, getting out of a chair, or during the first few minutes of activity after sitting for a while.
How It’s Diagnosed
A physical exam is usually enough. Your doctor can often identify bursitis by the location and feel of the swelling. Prepatellar bursitis in particular has a distinctive appearance: a well-defined, fluid-filled pocket sitting right over the kneecap, separate from swelling inside the joint itself.
If there’s concern about infection, a needle aspiration removes fluid from the bursa for lab testing. The fluid is checked for bacteria, white blood cell counts, and crystals (which would suggest gout rather than bursitis). Imaging like X-rays or MRI is typically reserved for cases where the diagnosis is unclear or symptoms don’t improve, to rule out other problems like a meniscus tear or fracture.
Treatment for Non-Infectious Bursitis
Most cases of knee bursitis improve with conservative measures: rest, ice, elevation, and over-the-counter anti-inflammatory medication. The key is removing whatever caused the irritation in the first place. If kneeling triggered it, stop kneeling. If running aggravated it, back off your mileage. Wrapping the knee with a compression bandage can help control swelling.
Swelling and pain typically resolve within a couple of weeks with consistent rest. If symptoms persist beyond two to three weeks, that’s a signal to follow up with your doctor. At that point, they may drain the fluid with a needle to relieve pressure and speed recovery.
Steroid injections into the bursa are an option but are used sparingly. They’re typically reserved for cases where fluid keeps reaccumulating despite rest, ice, compression, and anti-inflammatory medication, and only after infection has been ruled out through fluid analysis. One injection is often enough to break the cycle of inflammation.
Treatment for Septic Bursitis
Infected bursae need antibiotics, and the fluid usually needs to be drained, sometimes more than once. Steroid injections are specifically avoided in septic cases because suppressing the immune response in an infected area can make things significantly worse. Most people with septic bursitis recover fully with antibiotics and drainage, but the treatment course takes longer than simple bursitis, often several weeks of antibiotics.
When Surgery Is Needed
Surgery is uncommon for knee bursitis. It enters the picture when conservative treatment fails repeatedly, particularly in chronic cases where the bursa keeps refilling with fluid or in septic bursitis that doesn’t clear with antibiotics and drainage alone.
The procedure, called a bursectomy, removes the bursa entirely. It can be done through a traditional open incision or with a small camera and instruments (endoscopic approach). A study of 27 endoscopic bursectomies for stubborn septic bursitis reported good outcomes with no wound healing problems and only one minor recurrence. After removal, the body gradually forms new tissue in the area, though it may not perfectly replicate the original bursa’s cushioning.
Recovery and Long-Term Outlook
For a straightforward case of non-infectious bursitis, you’re looking at roughly two weeks to feel significantly better, assuming you actually rest the knee. Most people recover completely with no lasting effects.
The risk is letting it become chronic. If you push through the pain or keep doing the activity that caused it, bursitis can drag on for months or even years. Chronic bursitis involves a thickened bursa wall that stays inflamed at a low level and flares up with minimal provocation. It’s much harder to treat at that stage.
If your work or hobbies put you at risk, knee pads are the simplest preventive measure. Taking breaks from kneeling, using a cushioned mat, and strengthening the muscles around the knee all help reduce the chance of recurrence. For pes anserine bursitis, stretching the hamstrings and inner thigh muscles and maintaining a healthy weight are the most effective long-term strategies.