Baker’s Cyst basically is a fluid-filled cyst which causes bulging & a feeling of tightness behind the knee. This pain usually gets worse when the knee is fully flexed or extended or when the patient is active. Baker’s cyst is also known as the Popliteal Cyst. It is usually resulting from problems with the knee joint like cartilage tear or arthritis, as both these conditions can cause the knee to produce too much fluid that can lead to formation of Baker’s cyst. Although Baker’s cysts cause swelling which can make people uncomfortable, treatment of underlying problems will usually be able to provide relief.