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What is Bakers cyst and explain in detail?
A Bakers cyst, also known as a popliteal cyst, is a type of fluid collection behind the knee. Often there are no symptoms. If symptoms do occur these may include swelling and pain behind the knee, or knee stiffness. If the cyst breaks open, pain may significantly increase with swelling of the calf. Rarely complications such as deep vein thrombosis, peripheral neuropathy, ischemia, or compartment syndrome may occur.Risk factors include other knee problems such as osteoarthritis, meniscal tears, or rheumatoid arthritis. The underlying mechanism involves the flow of synovial fluid from the knee joint to the gastrocnemio-semimembranosus bursa, resulting in its expansion. The diagnosis may be confirmed with ultrasound or magnetic resonance imaging (MRI).Treatment is initially with supportive care. If this is not effective aspiration and steroid injection or surgical removal may be carried out. Around 20% of people have a Bakers cyst. They occur most commonly in those 35 to 70 years old. It is named after the surgeon who first described it, William Morrant Baker (1838–1896).

Signs and symptoms
Symptoms may include swelling behind the knee, stiffness, and pain. If the cyst breaks open, pain may increase, and there may be swelling of the calf. Rupture of a Bakers cyst may also cause bruising below the medial malleolus of the ankle (Crescent sign).

Cause
In adults, Bakers cysts usually arise from almost any form of knee arthritis (e.g., rheumatoid arthritis) or cartilage (particularly a meniscus) tear.   Bakers cysts in children do not point to underlying joint disease. Bakers cysts arise between the tendons of the medial head of the gastrocnemius and the semimembranosus muscles. They are posterior to the medial femoral condyle.
The synovial sac of the knee joint can, under certain circumstances, produce a posterior bulge, into the popliteal space, the space behind the knee. When this bulge becomes large enough, it becomes palpable and cystic. Most Bakers cysts maintain this direct communication with the synovial cavity of the knee, but sometimes, the new cyst pinches off. A Bakers cyst can rupture and produce acute pain behind the knee and in the calf and swelling of the calf muscles.

Diagnosis
Diagnosis is by examination. A Bakers cyst is easier to see from behind with the patient standing with knees fully extended. It is most easily palpated (felt) with the knee partially flexed. Diagnosis is confirmed by ultrasonography, although if needed and there is no suspicion of a popliteal artery aneurysm then aspiration of synovial fluid from the cyst may be undertaken with care. An MRI image can reveal presence of a Bakers cyst.
An infrequent but potentially life-threatening complication, which may need to be excluded by blood tests and ultrasonography, is a deep vein thrombosis (DVT).  Quick assessment of the possibility of DVT may be required where a Bakers cyst has compressed vascular structures, causing leg edema, as this sets up conditions for a DVT to develop.
A burst cyst commonly causes calf pain, swelling and redness that may mimic thrombophlebitis.

Treatment
Bakers cysts usually require no treatment unless they are symptomatic. It is very rare that the symptoms are actually coming from the cyst