What are the key clinical features that differentiate a Baker's cyst from other causes of posterior knee swelling?

Key clinical features differentiating a Baker's cyst from other causes of posterior knee swelling include:

• Location and nature of swelling: A Baker's cyst typically presents as a palpable swelling in the popliteal fossa (posterior knee), often associated with underlying joint pathology such as meniscal tears or arthritis, whereas other causes may have different anatomical locations or characteristics ¹.
• Association with underlying joint disease: Baker's cysts commonly arise secondary to intra-articular knee conditions like osteoarthritis or rheumatoid arthritis, and their presence often correlates with symptoms of these diseases ¹.
• Symptoms: The cyst may be asymptomatic or cause posterior knee discomfort and swelling; symptoms worsen with knee extension or activity. Other causes of posterior swelling, such as deep vein thrombosis (DVT), present with systemic signs like pain, redness, and warmth, and require urgent exclusion ¹.
• Imaging findings: Ultrasound or MRI can confirm a fluid-filled cyst communicating with the knee joint, distinguishing it from solid masses or vascular causes of swelling ¹.
• Red flags and urgent considerations: Presence of red flags such as signs of DVT or infection necessitates urgent assessment to exclude serious alternative diagnoses, which are not features of a simple Baker's cyst ¹.

In summary, a Baker's cyst is characterized by a well-defined, fluid-filled swelling in the popliteal fossa linked to underlying knee joint pathology, usually without systemic signs, and confirmed by imaging, which helps differentiate it from other causes of posterior knee swelling such as DVT, tumors, or soft tissue injuries ¹,².