Course Description:

A popliteal cyst, also known as Baker’s cyst, is an enlargement of a bursa in the popliteal space of the knee. Any bursa can be involved, but in most cases the gastrocnemio-semimembranosus bursa is the involved structure. Popliteal cysts are classified as primary or secondary. Primary cysts have no communication with the knee joint and are usually caused by trauma to the bursa or an isolated inflammatory condition. Secondary cysts, which are much more common in adults, have a communicating channel to the internal knee joint. The most common cause of secondary popliteal cysts is internal knee pathology that results in excess synovial fluid traveling from the knee joint, through the communicating channel, and into the involved bursa. Meniscal tears have been deemed the main preceding knee pathology in 71-82% of cases. The resulting bursitis can present as a palpable mass in the posterior knee. If swelling is considerable, patients may report tenderness to palpation, stiffness, limited end range of motion (ROM), and pain with activity (e.g., squatting, running). A complication of a popliteal cyst is that the enlarged bursa can rupture, extravasating its contents into the calf. This can result in other symptoms, including extensive pain, calf edema, and other signs, which can mimic a deep vein thrombosis (DVT). Thus, if such symptoms are ever observed, they should be considered indicative of DVT unless otherwise ruled out. Other conditions that should be ruled out are malignancy, aneurysm, and sepsis. Treatment for adults with popliteal cysts is conservative and includes a modification in activity levels to prevent aggravating or rupturing the cyst. However, recurrence of the popliteal cyst is very common and may warrant surgery.