A baker's cyst, also called a popliteal cyst, occurs when synovial (joint) fluid forms behind the knee and creates a visible swelling. You can develop a baker's cyst because of arthritis, rheumatoid arthritis, a meniscal cartilage tear or other damage to the knee.

A Baker's cyst, also known as a popliteal cyst, is a fluid-filled growth that causes swelling, tightness and bulging in the knee. This can lead to pain when the knee joint is moved, restricting its movement and strength.

Your knee may look like a simple structure from the outside, but on the inside it's a joint that's made up of many components, according to the American Academy of Orthopaedic Surgeons. Because your knee is so complex, it's highly susceptible to various injuries.

An ACL -- or anterior cruciate ligament -- injury is one of the most common knee injuries seen. These injuries usually occur in athletes who participate in high-impact sports including basketball, soccer and football. Surgery is often required to repair an ACL injury.

A knee immobilizer is a type of brace worn on the leg to lock the knee in extension and prevent motion of the joint. According to the American Academy of Family Physicians, a knee immobilizer is often used after an acute injury to the knee, such as a ligament rupture or a fracture.

Damage to the structures of the knee commonly causes inflammation and swelling, also called fluid on the knee. The swelling may occur suddenly after a traumatic injury to the knee, or it may be a long-term problem for patients with gout or arthritis.