Baker's cysts often have no symptoms, although there is sometimes slight swelling behind the knee, which may or may not cause pain. Cysts are usually soft and somewhat tender. The cyst behind the knee will feel like a water-filled balloon. In some cases, the cyst ruptures, causing pain, swelling, redness and bruising behind the knee and up into the calf. Pain, swelling and bruising behind the knee can also be a symptom of a blood clot, which requires immediate medical attention.
Cause and Risk Factors
Sometimes, especially in children, a normal lubricating fluid sac forms a connection with the knee, which can form a Baker's cyst. In adults, such cysts usually form by herniation of the knee joint capsule out into the back of the knee. When this occurs, the meniscal cartilage of the knee also commonly tears. In fact, almost any damage to cartilage in the knee can lead to the formation of a cyst. In older adults, Baker's cysts can form when there is degenerative arthritis in the knee.