Baker's cyst refers to a fluid-filled cyst behind the knee. It causes pain on full flexion or extension of the leg. Baker's cyst may occur as a result of arthritis or cartilage tear. Treatment usually involves steroid injected directly into the knee. Fluid drainage and physical therapy such as icing and compression are also helpful. Reference: https://www.mayoclinic.org/diseases-conditions/bakers-cyst/diagnosis-treatment/drc-20369955 Image via: https://www.consultant360.com/index.php/articles/bilateral-baker-cysts