What Is a Baker's Cyst?
A Baker's cyst (popliteal cyst) is a fluid-filled swelling behind the knee. It forms when excess fluid from the knee joint pushes into a small sac (bursa) at the back of the knee.
It's named after the surgeon who first described it, Dr. William Morrant Baker.
What Causes It?
The Underlying Problem
A Baker's cyst is almost always secondary to something else:
Arthritis:
Osteoarthritis (most common)Rheumatoid arthritisGoutMeniscus tears:
Damaged cartilage causes inflammationExcess fluid productionOther knee problems:
Ligament injuriesCartilage damageAny cause of joint effusion (swelling)The Mechanism
The knee joint produces extra fluid in response to irritation or injury. This fluid can push through a weak spot into the bursa at the back of the knee, creating the cyst.
Symptoms
The Cyst Itself
Visible or palpable lump behind kneeFeels like a water balloonMay change size (larger when knee is inflamed)Tightness or fullness behind kneeMay Be Asymptomatic
Many Baker's cysts cause no symptoms and are found incidentally.
When Symptomatic
Stiffness in kneeLimited bendingDiscomfort with prolonged standingPain behind kneeIf Cyst Ruptures
Sudden sharp pain behind kneeSwelling and redness in calfCan mimic DVT (blood clot)—important to rule outDiagnosis
Physical Exam
Palpable mass behind kneeMay transilluminate (light shines through)Usually non-tender unless inflamedImaging
Ultrasound:
Confirms cystRules out DVTShows communication with jointMRI:
Detailed viewShows underlying knee pathologyMeniscus, cartilage evaluationX-rays:
Don't show the cystMay show arthritisTreatment
Treat the Underlying Cause
This is the key. The cyst is a symptom, not the primary problem.
If arthritis:
Manage arthritis (exercise, weight loss, medications)Address inflammationIf meniscus tear:
May need surgical repairConservative management if appropriateConservative Treatment
Activity modification:
Avoid aggravating activitiesLow-impact exerciseIce:
After activity15-20 minutesCompression:
Can help with discomfortNSAIDs:
Reduce inflammationPhysical therapy:
Strengthen kneeMaintain range of motionAddress underlying mechanicsAspiration
When considered:
Large, symptomatic cystNot responding to conservative careHow it works:
Needle inserted to drain fluidOften combined with corticosteroid injectionOften recurs because underlying cause persistsSurgery
Rarely needed for the cyst itself
May be indicated when:
Underlying cause requires surgery (meniscus repair)Cyst is very large and causing nerve compressionRecurrent after aspirationIf the Cyst Ruptures
What Happens
Fluid leaks into calfSudden pain and swellingLooks like DVTWhat to Do
Rest and elevationIceCompression bandageSee doctor to rule out DVT (blood clot)Usually resolves on its ownRule Out DVT
Ruptured Baker's cyst and DVT can look identical. Ultrasound can differentiate. Don't ignore calf swelling—get it checked.
Living With a Baker's Cyst
Many People Do Fine
Small asymptomatic cysts can be left aloneMonitor for changesAddress if becomes bothersomeSelf-Care
Maintain knee healthStay active (low impact)Manage weightTreat underlying conditionsWhen to Seek Care
Sudden severe pain (rupture or DVT)Progressive swellingNumbness or weaknessSignificant functional limitationPrognosis
Outcomes
Cyst may resolve if underlying cause treatedMay persist but remain asymptomaticRarely dangerousRecurrence common if underlying cause not addressed
A Baker's cyst is a signal that something's going on in your knee. Don't ignore it, but also don't panic. Treat the underlying problem—arthritis, meniscus tear, whatever it is—and the cyst often takes care of itself. Draining it without addressing the root cause usually means it comes back.