Baker's cyst

What is a Baker's cyst?

A Baker's cyst, also known as a popliteal cyst, is a fluid-filled swelling that forms behind the knee. It occurs when excess synovial fluid, the lubricating fluid in the knee joint, accumulates in a bursa, which is a small sac near the joint. The cyst is typically located at the back of the knee, but its size and shape may vary, with some cysts being small and others large enough to cause noticeable bulging.

Causes

The primary cause of a Baker's cyst is an underlying knee problem that leads to inflammation of the synovial membrane, such as arthritis, meniscus tears, or other joint injuries. In these conditions, the knee produces excess synovial fluid in an attempt to reduce friction and improve movement. If the fluid cannot properly drain, it accumulates in the bursa, forming a cyst.

Symptoms

Symptoms of a Baker's cyst can vary, with some individuals experiencing no symptoms at all. When symptoms do occur, they typically include a noticeable bulge at the back of the knee, stiffness, or discomfort. In some cases, the cyst may cause pain when bending or fully extending the knee. If the cyst ruptures, which can occasionally happen, it may cause sudden sharp pain, swelling, and redness down the calf, and it may resemble symptoms of deep vein thrombosis (DVT).

Diagnosis

Diagnosis is typically made through physical examination and imaging tests such as ultrasound or MRI to confirm the presence of the cyst and rule out other knee issues.

Treatment

Treatment for a Baker's cyst depends on the underlying cause and the severity of symptoms. Conservative measures such as rest, ice, and anti-inflammatory medications may alleviate mild symptoms. For larger or more painful cysts, drainage or aspiration may be performed. In rare cases, if the cyst causes significant discomfort or doesn't resolve with other treatments, surgery to remove the cyst may be necessary.