Overview
A Baker cyst is a fluid-filled swelling that forms at the back of the knee, usually arising from the knee joint's lining (synovium). When the knee has inflammation or extra joint fluid, the fluid can track into a small sac near the tendons at the popliteal area, creating a lump or tightness. Baker cysts may cause discomfort, limited bending, and a feeling of fullness, especially when you are active. If the cyst ruptures, the fluid can irritate tissues in the calf and mimic other urgent conditions.
Symptoms
Many people notice a soft, sometimes firm lump behind the knee that may be more noticeable when standing. Pain, tightness, or aching can worsen with bending the knee, climbing stairs, or prolonged standing and walking. Some patients develop swelling or a heavy feeling in the calf if the cyst enlarges or if fluid spreads downward. Rarely, ruptured cysts can cause sudden calf pain and swelling that may look like a blood clot.
Causes
Baker cysts most often develop as a secondary problem from another knee issue, such as osteoarthritis, rheumatoid arthritis, or a meniscal tear. These conditions increase synovial inflammation and joint fluid, and that extra fluid can herniate into the popliteal bursa near the back of the knee. The cyst can also enlarge with continued knee irritation and may rupture when pressure becomes high.
Risk Factors
Your risk is higher if you have knee arthritis, inflammatory joint disease (like rheumatoid arthritis), or past or current meniscus problems. Activities or occupations that repeatedly stress the knee, as well as age-related joint wear, can contribute by increasing joint inflammation and fluid production. Being overweight can add extra load to the knee and may worsen underlying joint conditions.
Prevention
You can reduce the likelihood of recurrence by managing the underlying knee problem, such as keeping arthritis symptoms under control and protecting a healing meniscus. Strengthening the muscles around the hip and thigh, improving knee mechanics, and staying active with low-impact exercise can lower joint irritation. Maintaining a healthy weight and avoiding overloading the knee during flare-ups may also help limit joint effusion and cyst formation.
How the Diagnosis Is Evaluated
A clinician typically starts with a history of a lump behind the knee and associated pain, stiffness, and swelling patterns. A physical exam often helps confirm a mass in the popliteal region and assess knee range of motion and tenderness. Ultrasound is commonly used to visualize the fluid-filled cyst and to check whether it has ruptured or if symptoms could be from another cause, such as a clot. X-rays or MRI may be used selectively to identify the underlying knee condition driving the extra fluid.
Nonsurgical Treatment Options
Treatment focuses on calming the knee and reducing fluid production, rather than directly "curing" the cyst by itself. Rest from aggravating activities, activity modification, and short-term use of anti-inflammatory medications (if safe for you) can help reduce pain and swelling. Physical therapy can improve knee mechanics and strength to decrease stress on the joint and may help symptoms even if the cyst remains. If the cyst is large, painful, or causing significant limitation, ultrasound-guided aspiration may be considered to relieve pressure, often along with addressing the underlying joint problem. In cases where the cyst is tied to knee arthritis or inflammation, a clinician may also consider a corticosteroid injection into the knee joint to reduce effusion; platelet-rich plasma may be considered in some practices for selected osteoarthritis cases.
When to Seek Medical Attention
Seek prompt medical attention if you have sudden or rapidly worsening calf pain and swelling, especially if you have warmth, redness, or tenderness, because a ruptured Baker cyst can mimic a deep vein thrombosis. Go to urgent care or emergency services if you experience shortness of breath, chest pain, or coughing blood, since those can indicate a serious circulation problem. Contact a clinician soon if the swelling is persistent, significantly painful, you cannot bend the knee normally, or you develop fever or feel unwell. If you have new numbness, major weakness, or inability to bear weight, get evaluated urgently.
Frequently Asked Questions
It often feels like a tightness or a soft-to-firm lump behind the knee that may become more noticeable when the knee is straightened or when you stand.
Yes, a Baker cyst can rupture and cause sudden calf pain and swelling, which may resemble a blood clot and should be medically assessed.
Light, low-impact activity is often okay, but you should avoid movements that significantly increase swelling or pain and follow a clinician's plan for safe progression.
Next Steps
If you notice a new lump behind the knee or worsening swelling, schedule an evaluation to confirm the diagnosis and check for an underlying knee cause. If pain and calf swelling come on suddenly or you have symptoms that could suggest a clot, seek urgent care right away. In the meantime, avoid activities that sharply increase swelling and use gentle range-of-motion and low-impact movement as tolerated.