What is a Baker's Cyst? And what happened when mine burst...

Feb 26, 2020

I've never had a Baker's Cyst until post total knee surgery.  And I didn't know they could burst!  Boy-howdy does it hurt.  A burst Baker's Cyst can present like a lower leg blood clot so you can guess that I ended up in the emergency room to have it checked out.  Now that the scare is over, I'm sharing with you my research on exactly what a Baker's Cyst is and what happens when they burst.

What is a Baker's Cyst?

In plain terms, a Baker's Cyst (or Popliteal Cyst or Synovial Cyst) is a fluid filled sac behind your knee.  But what does that mean, exactly?  When you hear the term "cyst" your mind may go to "abnormal growth".  In the case of a Baker's Cyst, it is actually enlargement of a normally occurring bursa that sits fairly close to your skin at the back of your knee.  

A bursa is like a pillow that reduces friction typically at your joints between skin and tendon or tendon and bone.  You have over 150 bursae in your body.  The bursae sacs are lined by a synovial membrane that fills the sac with lubricating synovial fluid.  Synovial fluid is thick, like the white of a raw egg.  When a bursa becomes inflamed, it is called bursitis. 

Scientifically speaking, the Baker's Cyst bursa lies between the inside end (medial condyle) of the thigh bone (femur) and the tendons of your one of your hamstring muscles (semimembranosus) and one of your calf muscles (gastrocnemius).  This is one of four bursae at the back of your knee. It normally functions to reduce friction between those tendons and the bone.

The Baker's Cyst is sort of like the "spill over" tank for the knee.  The normally occurring bursa becomes a Baker's Cyst when it fills with excess synovial fluid most likely produced from the knee joint capsule.  You may see a bulge at the back of your knee and/or feel more pressure in your knee especially when you try to bend it.

Is a Baker's Cyst dangerous?

No, a Baker's Cyst is not dangerous, but it may be painful.  The important thing is to identify the underlying cause of the excess fluid (you'll see your doctor for diagnosis).  Sometime a doctor may drain the fluid and sometimes a Baker's Cyst may go away on its own.

However, mine burst!  I did not feel this happen, although it can feel like water running down the back of your calf.  What I noticed is that one night as I was lying in bed, I felt like my knee could be straightened a little easier.  The next morning I felt like I had pulled a muscle in my calf and then I saw the swelling in my lower leg that got worse over the next couple of days.  I contacted my orthopedic surgeon to see if this was of concern and he advised me to go immediately to the ER to be checked out because it sounded like a DVT or burst Baker's Cyst.  DVT is deep vein thrombosis or a blood clot in a deep vein which is very serious.

They conducted a Doppler Ultrasound which uses high-frequency sound waves to measure the amount of blood flow through your arteries and veins to detect if there was any abnormalities.   What they found was fluid drainage but no blood clot.  WHEW! Good news.

What a burst Baker's Cyst feels like...

My lower leg feels like a solid tube.  With the swelling, my calf measures 1 1/4 inch larger circumference than my other leg.  My ankle is now a "cankle" (thick like a calf and ankle fused).  I used crutches for a few days because walking was so painful.  I have very little doriflexion at my ankle (I can't much lift up my toes) which means I am walking with very short steps.  I'm wearing a compression sock and alternating ice and heat.  I elevate my leg above my heart (very difficult to do at work!) and massage my calf and knee every night. 

Check out my swollen right leg!

I get a lot of sympathy from my husband who says I look miserable.  It is very painful and swollen even one week after the burst. I'm not a very patient when it comes to waiting... Ultimately, you just have to wait it out and the excess fluid will eventually be reabsorbed by your body.  

~ Coach Robin

Robin Robertson
Founder: Healthy Knees Coach
Author: Healthy Knees Cycling (Healthy Knees Strength coming soon!)
Owner: Bellingham Training & Tennis Club



Bursae around the knee joint 


Knee Bursae https://radiopaedia.org/articles/knee-bursae?lang=us


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