The Real Reason Your Knee Is Swollen, According to Doctors
The knee is the largest joint in the body (and one of the most complex), meaning it’s also one of the most problem-prone. While knee strengthening exercises can help keep the joint in tip-top shape, if you find yourself with a swollen knee you’ll want to get to the root of the issue. From chronic conditions to acute injuries that can cause problems in the joint, the reason for your swollen knee might not be as obvious as you’d expect.
Medically known as edema, swelling can make everyday movements like walking and squatting difficult or even painful. Here, doctors explain the common culprits behind an enlarged knee.
Symptoms of a swollen knee
Your primary complaint when dealing with swollen knees may be the increased size, but Marc Matarazzo, M.D., a board-certified and fellowship-trained orthopedic surgeon specializing in sports medicine and related injuries, says that isn’t likely to be the only thing you’ll notice when your knee begins to get enlarged. He says the following symptoms are also common:
Pain
Tightness
Constriction
Instability
buckling
Tenderness
Redness
Warmth
Swollen knee causes
1. Injury
Whether you took a tumble during your workout or just walked smack into the coffee table, swelling is a normal reaction to injuries—including those around your knees. In fact, injuries are the most common reason for swollen knees that James Gladstone, M.D., chief of sports medicine at The Mount Sinai Health System, sees in younger, healthy patients.
“Injuries signal an inflammatory response in the body, which causes swelling,” Dr. Gladstone explains. Immediately post-injury, blood flow to the injured area increases, delivering the rush of fluids, proteins, and white blood cells needed to start the healing process. As a result, the injured area becomes red and swollen.
Two common knee injuries: a torn ACL (the ligament that runs across the front of your knee and connects the thigh and shin bones) and a torn meniscus (cartilage that acts as cushion between the thigh and shin bones).
2. Arthritis
A catch-all term for inflammation of a joint, arthritis is particularly common in the knee. It develops over time (often as you get older) and typically causes knees to swell, stiffen, and become painful or difficult to move.
Per the American Academy of Orthopaedic Surgeons, knees are most often affected by two forms of arthritis: osteoarthritis and rheumatoid arthritis. In osteoarthritis (the most common form), cartilage throughout the knee joint—which protects the ends of your bones—wears away over time. Meanwhile, in rheumatoid arthritis, the immune system attacks the joint, damaging its connective tissues and bones.
3. Gout
Technically a form of arthritis, gout occurs when high levels of uric acid (which is found naturally in the body) cause urate crystals to build up in your joint, leading to intense pain, swelling, and redness, per the Mayo Clinic.
Though gout often rears its ugly head in the joint at the base of the big toe, it can affect other joints throughout the body, including the knees, wrists, and fingers. According to Dan Paull, M.D., founder and CEO of Easy Orthopedics, gout often pops up in our extremities because these joints tend to be cooler in temperature—a more accepting environment for crystal formation.
First-timers likely won’t experience gout in their knee, however, people with a history of the condition may find that it manifests in different joints, Dr. Gladstone adds. Men, people who are overweight, and those with a family history are more likely to deal with gout, according to the U.S. National Library of Medicine.
4. Pseudogout
Also known as “false gout” or calcium pyrophosphate dihydrate deposition disease (CPPD), psuedogout can also cause swelling of the knee joint. Like gout, pseudogout is also considered a form of arthritis. Unlike gout, it primarily affects the wrists and knees. In pseudogout, a form of calcium crystals accumulate in joint cartilage and fluid, causing the same sudden joint pain and swelling as gout.
Pseudogout typically affects people over the age of 60, according to The Cleveland Clinic. People who have osteoarthritis, thyroid or metabolic issues, or kidney disease are also more likely to experience it.
5. Bursitis
Often confused with (but quite different from) arthritis, bursitis is another condition that can cause swollen knees. “Bursitis is a reaction in which sacks of fluids, blood vessels, and nerve endings that cushion your joints—called bursae—become inflamed,” explains Dr. Gladstone. Typically, bursitis occurs across the front of the knees as a result of excess pressure and friction on the joint over time.
“Those little blood vessels bleed and the bursa produces excess fluid, which creates this giant, swollen pouch—like a bubble of fluid just below the skin,” Dr. Gladstone says. These inflamed pouches, which can take on all sorts of shapes and sizes, can be incredibly painful to put pressure on.
Bursitis is most common in people who work a lot on their knees, like carpenters, plumbers, and tile-setters, says Dr. Gladstone. However, a good fall can cause bursitis, too.
6. Baker’s cyst
Also known as popliteal or synovial cysts, Baker’s cysts are fluid-filled lumps that develop on the back of the knee. According to Dr. Gladstone, they’re pretty common and nothing to be too alarmed about.
“Deep within the knee joint, there’s a layer of thin tissue called the ‘capsule’ between your bones,” Dr. Gladstone explains. When some sort of damage causes swelling within the knee joint, the pressure pushes extra fluid in the capsule out behind the knee joint, essentially creating what looks like a swollen ball at the back of the knee.
Not typically too painful, Baker’s cysts are often caused by arthritis or an acute injury within the knee. In some cases, they disappear on their own but often reoccur if you don’t treat the underlying cause.
7. An infection
Perhaps the most dire cause of knee swelling, infection in the knee joint warrants a hasty trip to the doctor. When an infection gets into the knee joint, “the knee quickly becomes really swollen, red, and hot,” says Dr. Gladstone. If untreated, infection can affect the whole body, causing fevers and body shakes.
Though a poorly-cleaned gash on the knee can lead to infection, infections elsewhere in the body (like urinary tract or respiratory infections) can make their way through the bloodstream and into joints, Dr. Gladstone explains.
8. Lyme Disease
The often-mysterious Lyme disease—a bacterial infection transmitted to humans through a tick bite—can affect the joints over time if left untreated. “Any time I see someone with knee swelling that doesn’t make sense for any other reason, I consider Lyme,” says Dr. Gladstone.
“We don’t fully understand how Lyme works, but it can manifest in many different ways, including joint swelling,” he explains. According to the Centers for Disease Control and Prevention (CDC), the knees are particularly susceptible to severe Lyme-related arthritis, pain, and swelling.
It’s worth noting, though, that these symptoms show up as the disease advances (days to months after the initial bite). Earlier signs of Lyme disease include the telltale bullseye-shaped rash and flu-like symptoms, such as fatigue, fever, headaches, muscle pain, and neck stiffness. Given Lyme’s murky mechanisms, treatment is relatively straightforward and involves a course of antibiotics to wipe the bacteria out of the body.
9. An autoimmune condition
In addition to rheumatoid arthritis, a number of other autoimmune conditions—in which the immune system attacks the body in various ways—can contribute to swelling and pain throughout the body, including in the knees. (According to the American Autoimmune Related Diseases Association, there are more than 100 kinds of autoimmune conditions out there.)
“Though less common, systemic autoimmune conditions, like lupus, may cause swelling,” Dr. Gladstone says. Like Lyme, these conditions may explain inflammation in the knees when nothing else can. Along with pain and swelling, people with autoimmune conditions often experience chronic fatigue, muscle aches, and low fevers.
Swollen knee treatments
Injury: When your swelling is the result of an injury, the doctor says you should rely on the RICE treatment: Rest, Ice, Compression, and Elevation.
Arthritis: If arthritis is to blame, Dr. Matarazzo says you can try a few different options to find relief, like ice, compression, elevation, nonsteroidal anti-inflammatory medications, corticosteroid injections, hyaluronic acid injections, platelet-rich plasma (PRP) injections, and gross factor injections.
Gout: For those suffering from gout, you’ll need to consult with your doctor. Dr. Matarazzo says they may prescribe nonsteroidal anti-inflammatory medications, anti-gout medications, corticosteroid injections, or even suggest dietary restrictions.
Pseudogout: When pseudogout is to blame, you may be looking at nonsteroidal anti-inflammatory medications, or corticosteroid injections, according to the doctor.
Bursitis: For bursitis, Dr. Matarazzo says you’ll usually be given nonsteroidal anti-inflammatory medications, corticosteroid injections, or PRP injections.
Baker’s cyst: A Baker’s cyst can normally be treated with nonsteroidal anti-inflammatory medications, corticosteroid injection, PRP injection, or arthroscopy, according to Dr. Matarazzo.
Infection: You’ll definitely need to see a medical professional if an infection is to blame, which the doctor says can typically be resolved with fluid and antibiotic injections. He says you’ll also usually see a surgical intervention, especially when it involves the joint.
Lyme disease: After being diagnosed with Lyme disease, Dr. Matarazzo says you’ll be treated with medications like nonsteroidal anti-inflammatory medications or antibiotics.
Autoimmune conditions: If you’re dealing with swelling related to an autoimmune condition, treatments typically involve nonsteroidal anti-inflammatory medications, corticosteroid injections, biologic medications, or oral corticosteroids.
When to see a doctor
There are plenty of times when people may try to treat their aches and pains at home or with over-the-counter solutions, but Dr. Matarazzo says there are a few symptoms that should have you reaching out to your family doctor.
If you’re experiencing an inability to bear weight, fevers, chills, sweats, deformity on or near your knee, unrelenting pain, drainage, an inability to bend the joint, or instability you’ll want to be seen as soon as possible.
Swollen knee prevention
Some causes of swelling can be harder to prevent than others, like when it comes to an injury or an infection, but Dr. Matarazzo says there are a couple of things you can do to keep your knee in good shape, like maintaining good muscle mass and tone. “Use natural anti-inflammatories such as turmeric, antioxidants, glucosamine, and arnica capsicum [to] reduce swelling as well,” he adds.
You Might Also Like
