Baker Cyst

A Baker cyst is a small, fluid-filled bump that forms on the back of your knee. Healthcare providers sometimes call Baker cysts popliteal cysts and synovial cysts. These are all different names for the same issue.

Baker cysts develop when something damages your knee joint or the tissues around it and extra fluid drains out of your knee. The fluid can only drain in one direction — out the back of your joint. That buildup forms the sac that becomes a Baker cyst.

Baker cysts are benign growths. That means they aren’t tumors and are never a symptom of (and don’t cause) cancer.

Visit a healthcare provider as soon as you notice a new growth or lump behind your knee, especially if you recently injured your knee or have arthritis.