What Exactly Is a Baker’s Cyst—And Can You Get Rid of It?

I’m generally not enthused about lumps and bumps of any variety on my body. But two years ago, I discovered one in particular that deeply unsettled me: a softball-sized mass behind my right knee.The lump seemingly appeared overnight, and though it wasn’t painful, I was alarmed by its size and unexplained presence. So I booked an appointment with a sports medicine doctor. He took my history, did a physical exam, and ordered an x-ray and MRI.Once the imaging results came back, he nonchalantly broke the news: I had a Baker’s cyst.Though I’d never heard the term before, I learned that Baker’s cysts are actually really common. One study involving 399 people with knee pain found that 26 percent had a Baker’s cyst. And up to 40 percent of people with osteoarthritis have them, according to separate research.Because I didn’t have other symptoms alongside the cyst—such as knee pain, swelling, or joint instability—the doctor told me to ignore it and continue with my usual exercise routine. He also told me I’d likely have the cyst for the rest of my life … which was a difficult and confusing pill to swallow.After delivering this news, the doctor rushed off to his next patient, leaving me with a growing list of questions about Baker’s cysts.The first thing I had to learn about this seemingly odd ailment is how it even happened, and why they happen.A Baker’s cyst is an overflow of fluid from the knee joint that collects at the back of the knee, Salvador Portugal, DO, a physician specializing in physical medicine, rehabilitation, and sports medicine at the NYU Langone Orthopedic Center, tells Runner’s World.Typically, the fluid flows from the knee joint to the backside through a one-way valve system, Vikas Shahi, MD, a sports medicine physician at Hospital for Special Surgery, says. So a Baker’s cyst is technically not a true cyst because it’s not actually enclosed in all spaces, he explains.For some people—like me, ugh—the cyst is always visible. But in most cases, the cyst can grow and shrink in size depending on the amount of overall fluid in the knee, Portugal says. In fact, Portugal has a Baker’s cyst himself and says that it fluctuates between being a noticeable bulge and totally invisible.Now for the culprit on why I got one.Baker’s cysts themselves are not problematic, but they’re often caused by underlying issues with the knee joint, Shahi says. The most common cause he sees in his clinic is osteoarthritis, which causes fluid buildup in the knee that can eventually spill over to the backside and form the cyst. ACL tears, meniscal tears, or tears to other parts of the knee cartilage can also be to blame, Portugal adds. Another reason: Inflammatory arthritis, which can trigger the knee to produce excess fluid, Shahi adds.I’m not certain what’s behind my Baker’s cyst; the doctor who diagnosed it didn’t touch on possible causes. But my MRI results did reveal a meniscus tear that I had no idea was there, so my hunch is that that’s a contributor (if not the sole cause).Sometimes, the pressure of fluid buildup in a Baker’s cyst can cause pain on the backside of the knee. But for many people—including moi—it’s painless. So unless you’re regularly inspecting the backs of your knees, you may not notice that it’s there. “A lot of times, patients are walking around with it and it doesn’t cause any symptoms,” Shahi says.It’s unsurprising, then, that many people don’t realize they have a Baker’s cyst until they get an MRI for a different reason (such as having generalized knee pain that doesn’t improve with physical therapy or anti-inflammatories), Portugal says. The gold standard for diagnosing a Baker’s cyst is with an MRI and an ultrasound, according to Shahi.🩺 When to See a Doctor About a Baker’s Cyst: A Baker’s cyst isn’t dangerous. But if you have swelling or pain on the back of your leg, particularly around the back of your knee or calf, you should have that evaluated, possibly in an urgent care, to make sure it isn’t a blood clot (which could potentially be life-threatening), Portugal says. Once your lump is confirmed as a Baker’s cyst, “it’s not so alarming,” Portugal says. But you still may want to pursue additional medical care if you’re having a hard time managing any associated symptoms, like knee pain or swelling, he says.Now the real question as an active person: Did I have to modify my training?Though my doctor told me to keep exercising as usual, I worried that running regularly might cause it to increase in size. But Portugal provided reassurance, telling me that people only need to modify their run training if the cyst causes pain with running or leads them to alter their mechanics.Portugal also pointed out that running may increase the thickness and volume of certain areas of the knee joint cartilage, making it a “healthy” activity for your knee, he says. And Shahi, for his part, highlighted research showing that runners with arthritis had fewer episodes of pain and better functioning compared to nonrunners with arthritis. “This shows that running seems to provide some sort of protective element,” he says.That said, it’s important to make sure your running form is on point. That’s because biomechanical errors caused by weak glutes and core muscles (or just an inability to properly engage them while running) can place more pressure on the knee, triggering inflammation there that could possibly worsen a Baker’s cyst, Shahi says.My million-dollar question, though, was: Does this have to be here forever?! My Baker’s cyst doesn’t cause me any pain or discomfort, but I really don’t like the look of it. The doctor who diagnosed it said he could aspirate it for me, which would involve sticking a big needle in it to drain the fluid. But he quickly caveated that he wouldn’t recommend that option, because Baker’s cysts often come back after aspiration. “I’ve had patients go home and call me immediately saying they filled right back up,” he says.Portugal told me most physicians have a similar mindset of discouraging aspiration because of the belief that the cyst will likely come back. But after doing a more recent search of the scientific literature, Portugal said the incidence of Baker’s cyst recurrence after aspiration seems to be much lower than what is commonly taught. So if someone’s Baker’s cyst is really symptomatic—meaning, it’s causing significant pain and interfering with daily life—he thinks aspiration is a “reasonable thing to try.”In general, though, if a Baker’s cyst isn’t that bothersome, Portugal doesn’t recommend anything beyond possibly physical therapy and taking an anti-inflammatory medication.Another, more serious option for getting rid of the cyst is getting surgery to fully remove it. But this is typically only done in conjunction with an already scheduled knee surgery, such as a knee replacement. “It is incredibly rare that a surgeon will take somebody to the operating room just to remove the cyst,” Shahi says.Aspiration and surgery aside, there are some “low-hanging fruit” things you can try to shrink the cyst, Shahi says. These include icing it every night or dabbing on some Voltaren Gel (an over-the-counter anti-inflammatory cream) to reduce inflammation in your knee and hopefully diminish the corresponding fluid buildup. These measures can sometimes help, Shahi says, though they likely won’t eliminate the cyst completely. “You’re probably still going to have sort of these waxing and waning episodes,” he says.A better approach, Shahi says, is to understand why fluid is developing in your knee in the first place. And if you address that—for example, by taking steps to better manage arthritis with physical therapy or injections, or repair a meniscus tear—then the cyst will likely shrink, if not fully resolve on its own. Beyond that, incorporating regular mobility work (such as yoga) and emphasizing core and glute strength/activation work in tandem with your running can help reduce extra strain on your knees that may be contributing to the cyst.Final thing to know: Baker’s cysts sometimes spontaneously rupture due to too much pressure being built up, Shahi says. For some people, the cyst is then gone for good. But for others, it can return later on.After hearing all this, I took a two-pronged approach to my Baker’s cyst. Part one: Acceptance.Like I said, I don’t enjoy the look of the lump, but I’m doing my best to stew less over its existence and instead focus on the fact that I’m still healthy and able to move pain-free.Part two: I’ve ramped up my overall strength training regimen, which means I’m doing more glute and core work than ever. Perhaps as a result, my cyst recently shrunk from softball-sized to golf ball–sized, which I absolutely count as a win!Jenny is a Boulder, Colorado-based health and fitness journalist. She’s been freelancing for Runner’s World since 2015 and especially loves to write human interest profiles, in-depth service pieces and stories that explore the intersection of exercise and mental health. Her work has also been published by SELF, Men’s Journal, and Condé Nast Traveler, among other outlets. When she’s not running or writing, Jenny enjoys coaching youth swimming, rereading Harry Potter, and buying too many houseplants.