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Baker’s Cyst. Swelling Behind My Knee.


    I fight the urge to sing the notorious hit “I Wan’t It That Way” by the Backstreet Boys as I start to write nearly EVERY article… “Tell me why?!?” Swelling behind the knee is a common finding, often labeled as a Baker’s Cyst (or Popliteal Cyst). Sometimes it is accompanied by pain and sometimes it isn’t. You might have painful swelling behind the knee right at this moment. You may also feel the same swelling on the other side without any complaints of pain. So I know what you are thinking, or singing, “tell me why?!” We have fluid filled sacs called bursae in various regions throughout the knee that serve a purpose. Your Baker’s Cyst is actually one of these bursae. A Baker’s Cyst specifically refers to a bursae (fluid filled sac) located at the inner portion of the knee between the head of the calf tendon and hamstring tendon (gastrocnemius and semimembranosous if you like specifics).

    Bakers cyst


    What Purpose Does This Bursae Serve?

    1. Reduce Friction
      • They reduce friction between the tendons and bone in that region.
    2. Reduce Pressure From Fluid In the Knee Joint 
      • When the knee joint swells we have valves between some of these bursae and the knee joint. The bursae will fill up with fluid to reduce pressure within the knee joint. It is a beautiful system!

    Determining whether or not the bursae is the source of pain is hard to do. Understanding that the bursae, or Baker’s Cyst, is a friction eliminator and fluid collector helps guide us in treating it [treatment options later in article]. 

    In a study performed in 1938 by Wilson, 26 out of 30 dissected knees had this bursae present. Out of 26 approximately 15 of the bursae had a valve between the bursae and the knee joint that allowed the flow of fluid from the knee joint into the bursae. I know what you are thinking. “Can the bursae send fluid into the knee joint?” As far as we know, it cannot. It is a one way valve (Taylor, 1973).

    How Do I Know If I have A Baker’s Cyst?

    Common Findings:

    • Swelling behind the knee joint
    • Aching behind the knee joint
    • Increased pain with straightening the knee
    • “Foucher Sign”– Firmness behind the knee when fully straightened and softening when the knee is flexed. This is often used by your physician to determine if the mass behind your knee is or isn’t a Baker’s Cyst. Other possibilities include an aneurysm of the artery behind your knee, a cyst in the artery behind your knee, tumor or ganglion cyst (Canoso, 1987).

    Ganglion Cystscyst that develops local to a joint or tendon. Also filled with fluid, more commonly found local to the wrist and hands. 

    bakers cyst pic lady.jpg

    What Test Will Tell Me If This Is A Baker’s Cyst?

    “I want to know exactly what is going on.”

    Ultrasound is cheap and can be used to confirm the development of a cyst behind the knee. Unfortunately, it is not very accurate in differentiating between specific types of cyst (baker’s cyst vs. meniscal cyst). It is also unable to differentiate between a cyst and a fluid filled tumor. Last but not least, it won’t tell you much about other potential knee issues (meniscus tear, ligament tears, tendon tears and degree of arthritis).

    Meniscal cyst– cyst caused by the protrusion of fluid from a meniscus tear. 

    The Gold Standard: Magnetic Resonance Imaging (MRI). MRI however is more specific. It can more accurately confirm that the swelling is or isn’t a bakers cyst. It can identify other knee issues. Lastly, it can rule out some of the more red flag issues. Like tumors and arterial aneurysms.


    Why Is My Baker’s Cyst Swollen?

    Without a thorough evaluation from a medical provider we can’t definitely say. With that said, I encourage you to schedule a visit with a physical therapist. If you aren’t seeing progress after 2-4 weeks follow up with your physician. 


    Physical Therapy First? Why?

    1. The reason I encourage a short bout of physical therapy first is that this pain can easily be managed with some good guidance.
    2. Second, if you are over 30 years old I would bet all the money in my pocket ($2 and a 1/2 off coupon at Chipotle) that you WILL find some wear and tear at your knee with MRI. It is often the equivalent of having wrinkles. No one is surprised when those things show up! Most insurances won’t even pay for an MRI until you have tried physical therapy.

    knee PT.jpg

    With some hesitation I will tell you that….

    It was reported that 94% of patients with Baker’s Cysts also have some wear and tear at the knee joint. Knee disorders include tears in knee cartilage, ligaments and at the meniscus. With meniscus tears being the most common finding. Arthritis is also another common findings, as well as local swelling within the knee joint.

    Fun Facts:

    • 50% of people with knee arthritis have no reported pain (Bedson and Croft, 2008)
    • 35% of collegiate basketball players without reported knee pain have notable abnormalities on MRI (Major and Helms, 2002).

    Just because you have notable findings on MRI does not mean that it is definitively the source of your pain. Learn more about the complexity of pain here. 


    Reasons to Consider an MRI First?

    Trauma. Immediate swelling after a fall or twisting the knee joint, followed by difficulty bearing weight deserve some immediate attention.

    If your pain slowly developed over time taking a more conservative route is appropriate.


    Treatment Options:

    Consider a statement made earlier. 

    When the knee joint swells we have valves between some of these bursae (fluid filled sacs) and the knee joint. The bursae will fill up with fluid to reduce pressure within the knee joint. It is a beautiful system! Determining whether or not the bursae is the source of pain is hard to do. If you consider its role as a friction reducer and fluid collector the answer to your pain should become clearer.”

    The Answer: Reduce Swelling and Inflammation.

    1. Activity Modification

    Remove or modify the activity that is causing your pain. If you love running, but your knee is more swollen and painful after, we need to make a change. If you love CrossFit, but your knee hurts after squats we need to make a change. If your only source of exercise is walking your dog, but it makes your knee hurt we need to make a change.

    This could be less repetitions in the gym, slower runs or shorter distances when walking your dog. I am not saying FOREVER. Only for the mean time. Just because you want to run a marathon today does not mean your body has the capacity too. Depending on your level of fitness, walking for 1/2 a mile while carrying your son may be enough to irritate your knee. 


    1. I. C. E. [Ice. Compression. Elevation.]

    Make time to elevate the leg with the knee above the heart, apply some ice and add compression to the knee to help get swelling out the the knee. I purposely didn’t put too much emphasis on REST. I prefer “activity modification.” Motion is lotion. Shutting everything down and becoming a couch potatoe for 2 weeks won’t do you any good. A little pain with activity is ok, you can poke the bear. When it starts getting angry back off some. 

    Frequency: 2-3x/day if possible for 20 minutes at a time.

    Other Options:

    • Kinesiotape is another option that may help reduce local swelling behind the knee. In clinic, the addition of kinesiotape tends to quickly show a reduction in local swelling and bruising. 
    1. Stretch and Foam Roll

    Earlier we mentioned that straightening your knee often becomes difficult as the knee swells. With more swelling, bending the knee may also become tough. Before you return to exercise you want to make sure you have the appropriate amount of flexibility around the knee. Spend time restoring this flexibility. It will help you move freer and with less pain. The main muscles that you will be targeting are your hamstrings and calf muscles. Both of which cross behind the knee joint. Improving flexibility within these muscles will allow you to straighten your knee.

     Combining stretching with some soft tissue work is a good 1, 2 punch! This could include massage, dry needling or some foam rolling. Treating the calf and hamstring muscles can help eliminate trigger points that could be creating pain behind your knee. In the picture below, you can see how trigger points at the hamstring and calf refer directly behind the knee. 

    Gastrocnemius trp

    Biceps Femoris, Semitendinosus, Semimembranosus

    1. Strength and Balance

    Be weary with this one. Most therapists, physicians and fitness trainers are quick to tell people that they are “weak.” In most situations, reducing pain at the knee and restoring flexibility will get you 90% of the way there. Identifying specific strength and balance deficits, and designing a program can be done more effectively if you see your physical therapist. Keep in mind, if you have been dealing with pain at your knee for an extended period of time you will have likely compensated in the way you were moving. Restoring some strength around the leg and normalizing the way you move could be super helpful. 

    Another thing to consider is the possibility of hamstring and/or calf tendinopathy (behind the knee). This could also be a source of your pain. Remember, your bursae help reduce friction between tendons and the knee joint. If the tendon is irritated, performing strengthening exercises focused on eccentric motions is often helpful for healing tendons. 

    balance yoga.jpg

    1. Weight

    In most studies we find that being overweight can obviously put more strain on your knees. We want to reduce strain at the knees. This will reduce swelling and result in a happier knee joint!

    1. Anti-Inflammatory Diet

    We don’t realize how much inflammation and swelling we trigger in our own body because of the foods we take in. In another article that we wrote about arthritis, we quickly mention foods that commonly spark inflammation. Breads, pastas, dairy, sugar, red meats to name a few. Often times, people have specific allergies to foods that will cause an inflammatory response. For example, peanuts. An upset stomach is not the only sign that certain foods don’t sit well with us. Joint discomfort, fogginess and fatigue are other examples that are often overlooked. 

    anti inflammatory food.jpg

    1. Sleep

    We always find a way to slip sleep into our articles. In our society, a lot of emphasis is placed on the “grind” or “hustling.” Unfortunately, we see increased reports of pain and depression in those who are not getting adequate sleep. Increased inflammation is also present with sleep deprivation (Mullington, 2010).  How much sleep do you need? In another post we go into more depth on this. 


    I Tried PT and All Your “Wonderful” Recommendations. Now what?

    If your Physician has confirmed that the bump behind your knee is a Baker’s Cyst the first option is usually:

    1. Cortisone Injection

    Cortisone Injections have been found to be helpful in reducing the size and symptoms of cysts (Acebes, 2006).

    1. Surgery

    In most cases, surgery on a suspected knee joint issue (meniscus tear, ACL tear, etc.) will usually be considered a final option. Especially if they are confident that your tear is not acute (a recent injury, opposed to a chronic injury that developed months or years ago). Baker’s Cysts are not removed until it is considered exceptionally large and a main contributor of your pain. Removal of Baker’s Cysts have not showed great results for pain reduction. In many cases, the cysts will redevelop with time. Remember, the cysts often develop in response to increased friction or swelling local to the knee joint. We want to treat what is causing the selling and inflammation.



    Big takeaways include:

    • Bursae are created by the body to reduce friction and help reduce pressure at the knee when it fills up with fluid. 
    • Bursae, more specifically your Baker’s Cyst, may or may not be the source of your pain. Many people have pain free bursae behind their knee. Compare by feeling behind your other knee.
    • Reducing inflammation and restoring flexibility at the knee should be your primary goal when attempting to reduce swelling behind the knee. 
    • Meniscus tears are most commonly linked to Baker’s Cysts. However, meniscus tears and other wear and tear at the knee are common findings in people WITHOUT pain. 
    • Unless you sustained a traumatic injury to the knee, consider conservative care first before seeing your physician. Insurance companies often want to see that you attempted physical therapy before paying big bucks for an MRI. 

    As always, proper pacing with your exercise and activities, and good lifestyle choices tend to help resolve most injuries. Do not hesitate to see a medical provider to get a program tailored specifically to you. Go forth and conquer! 


    -Dr. Michael Infantino, DPT



    Neurohistology of the subacromial bursa in rotator cuff tearYasuharu, Tomita et al.Journal of Orthopaedic Science , Volume 2 , Issue 5 , 295 – 300

    Frush, T. J., & Noyes, F. R. (2015). Baker’s Cyst: Diagnostic and Surgical Considerations. Sports Health7(4), 359–365. http://doi.org/10.1177/1941738113520130

    Wilson PD, Eyre-Brook AL, Francis JD. A clinical and anatomical study ofthe semimembranosus bursa in relation to popliteal cyst. J Bone Joint Surg Am. 1938;20:963-984.

    Taylor AR, Rana NA. A valve: an explanation of the formation of popliteal cysts. Ann Rheum Dis. 1973;32:419-421

    Canoso JJ, Goldsmith MR, Gerzof SG, Wohlgethan JR. Foucher’s sign of the Baker’s cyst. Ann Rheum Dis. 1987;46:228-232.

    Major and Clyde A. Helms. MR Imaging of the Knee: Findings in Asymptomatic Collegiate Basketball Players. American Journal of Roentgenology 2002 179:3, 641-644

    Bedson, J., & Croft, P. R. (2008). The discordance between clinical and radiographic knee osteoarthritis: A systematic search and summary of the literature. BMC Musculoskeletal Disorders9, 116.

    Acebes JC, Sanchez-Pernaute O, Diaz-Oca A, Herrero-Beaumont G. Ultrasonographic assessment of Baker’s cysts after intra-articular corticosteroid injection in knee osteoarthritis. J Clin Ultrasound. 2006;34:113-117.

    Mullington, J. M., Simpson, N. S., Meier-Ewert, H. K., & Haack, M. (2010). Sleep Loss and Inflammation. Best Practice & Research. Clinical Endocrinology & Metabolism, 24(5), 775–784. http://doi.org/10.1016/j.beem.2010.08.014

    5 thoughts on “Baker’s Cyst. Swelling Behind My Knee.”

    1. I just happen to stumble on your article just looking for the anatomy of the knee & why I have swelling behind my knee. I delightfully found your article. I can begin to tell you how useful and effective the information you provided. The knowledge and the physical therapy exercises you gave instruction on to alleviate pain & swelling behind the knee was perfect and on time for me. Thank you so much for sharing. God’s Blessing.

    2. Michael! Similar to the above commenter, this video helped me immensely. I have been to physical therapy for 1.5 years and then saw a doctor for my knee and no relief. I’ve done these exercises for 2 days now and I am flabbergasted that I can walk again with no pain. I have tears in my eyes as I type this to you. Thank you. I signed up for a call a few days ago- not sure if you still use that google doc form. I would just love to send you some money to pay it forward for helping me.

    3. Pingback: Strategies For Preventing Running Injuries • Rehab Renegade

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