Start your One-Week Free Trial
Already subscribed? Log in »
Popliteal cyst (Baker's Cyst)
Overview
A popliteal cyst (Baker's cyst), is a cystic enlargement of the bursa behind the knee (the gastrocnemius-semimembranosus bursa). They occur due to an abnormal inflow of synovial fluid from the knee's synovial joint (typically in the setting of arthritis).
Causes
In children, they occur due to structural (primary anatomical) processes.
In adults, they are typically associated with arthritis (eg, rheumatoid arthritis, osteoarthritis, etc...).
Presentation
Most popliteal cysts are asymptomatic and are simply an incidental finding on a radiographic study. Popliteal cysts can be the cause of calf pain (due to the swelling in the back of the knee) but it’s critical to exclude DVT (deep vein thrombosis) in patients with calf pain. DVT is a potentially life-threatening condition because it can lead to pulmonary embolism (PE).
Relevant Anatomy
From medial to lateral in the posterior knee lie the:
- Saphenous vein
- Semimembranosus muscle/tendon
- The gastrocnemius-semimembranosus bursa (popliteal cystic dilation)
- Medial head of the gastrocnemius
- Popliteal artery and vein + Tibial nerve
- For a detailed review of the cross-sectional anatomy of the posterior knee, see Arthroscopic Treatment of Popliteal Cysts
Pathophysiology
In adults, the typical factors that produce a popliteal cyst are trauma/inflammation that increases synovial fluid volume/pressure and a breakdown of the barrier between the synovium and the posterior knee bursa. Via a valve-like effect synovial fluid is forced into the bursa and dilates it.
They have the potential to cause harm through compression and rupture of adjacent posterior medial knee structures.
Treatment
Treatment involves reducing contributing inflammatory conditions, draining fluid when necessary, and surgically excising the cyst (as a measure of last resort).
- Anti-inflammatory medications.
- Arthrocentesis to remove excess fluid.
- Intraarticular injection with glucocorticoids to reduce local swelling.
- Surgical excision of cyst when necessary.