A Baker’s cyst, or popliteal cyst, is a fluid-filled swelling that develops at the back of the knee due to accumulation of synovial fluid. It often arises from underlying joint conditions such as osteoarthritis, arthritis, or meniscal tears, which increase joint fluid production.

Typical signs include a visible or palpable swelling behind the knee, tightness, pain especially during flexion, and in some cases, stiffness or restricted motion. The cyst may fluctuate in size and, if ruptured, can cause sudden pain and swelling in the calf.

Diagnosis is primarily clinical and confirmed by ultrasound or MRI, which help rule out other conditions like deep vein thrombosis. Treatment targets the underlying joint issue (e.g., inflammation or injury) and may involve physiotherapy, anti-inflammatory drugs, or in select cases, aspiration or surgical removal.

If untreated, it can compress nearby structures, limit joint motion, or rupture, mimicking deep vein thrombosis. Managing the underlying cause is crucial to prevent recurrence.