A Baker’s cyst, also known as a popliteal cyst, is a fluid-filled sac that forms behind the knee. It develops when the knee joint produces too much synovial fluid, the natural lubricant that reduces friction during movement. This excess fluid then accumulates in a bursa at the back of the knee, leading to a noticeable bulge. Baker’s cysts are often associated with underlying knee problems, such as arthritis or cartilage tears, which cause increased fluid production within the joint.
Key Signs and Symptoms
Common signs and symptoms of a Baker’s cyst involve discomfort and changes in knee sensation. Many individuals experience knee pain, which can range from a dull ache to a sharper sensation, particularly behind the knee. This pain frequently worsens with increased physical activity or after prolonged periods of standing, as these actions can put more pressure on the cyst.
Stiffness or tightness at the back of the knee is also common. This stiffness can make it difficult to fully bend or straighten the knee, limiting its range of motion. Some people also report a general feeling of fullness or a distinct lump behind the knee. Symptoms can fluctuate, but often persist if the underlying knee issue remains.
Physical Appearance and Feel
A Baker’s cyst manifests as a palpable lump located at the back of the knee. It typically forms on the inner side of the popliteal fossa, the hollow area behind the knee. Cyst size varies, from non-palpable to a large, visible mass.
When touched, the cyst often feels soft and fluid-filled, sometimes compared to a water balloon or a squashy orange. Its texture can change depending on knee position; it may become firmer when the knee is fully extended and softer or even disappear when the knee is bent to about 45 degrees. This characteristic change in firmness with knee movement is sometimes referred to as Foucher’s sign.
Associated Symptoms and Potential Complications
A Baker’s cyst can also limit knee range of motion, especially full flexion. Some individuals might experience clicking or locking sensations within the knee joint. Muscle weakness in the affected leg can also occur, particularly if the cyst becomes large enough to compress surrounding structures.
A complication arises if a Baker’s cyst ruptures. Rupture typically causes sudden, sharp pain in the knee and calf, often with swelling, redness, and warmth. Fluid from the ruptured cyst can leak into calf tissues, sometimes causing a sensation like water running down the leg or bruising around the inner ankle. These symptoms can closely mimic a deep vein thrombosis (DVT), which is a serious blood clot, necessitating prompt medical evaluation to distinguish between the two conditions.
When to Seek Medical Advice
Seek medical attention if Baker’s cyst symptoms are severe, persistent, or interfere with daily activities. A doctor can confirm the diagnosis and help rule out other conditions that might present similarly. Prompt consultation is important if you experience sudden, worsening pain, increased swelling, redness, or warmth in the calf, as these could indicate a ruptured cyst or a blood clot. Early assessment ensures appropriate management and helps prevent complications.