What are the signs and symptoms of a Baker's (popliteal) cyst of the right knee?

Signs and Symptoms of Baker's Cyst of the Right Knee

Baker's cysts present with swelling and tenderness behind the knee, which may worsen with exercise and can be present at rest, unlike intermittent claudication symptoms. 1

Clinical Presentation

• Baker's cysts (popliteal cysts) are fluid accumulations in the bursa of the gastrocnemius or semimembranosus muscles that frequently communicate with the knee joint space 2
• Swelling behind the knee is the most common presenting sign, typically located in the posteromedial region of the knee 3
• Tenderness in the popliteal fossa is a common symptom 1
• Pain may be present and can worsen with knee movement or exercise 1, 2
• Symptoms are not intermittent like vascular claudication - they can be present at rest 1
• The cyst may cause a feeling of tightness or fullness behind the knee 2, 4

Distinguishing Features

• Baker's cysts have a characteristic comma-shaped appearance when visualized with ultrasound between the medial head of gastrocnemius and semimembranosus tendon 1, 2
• Unlike peripheral artery disease, symptoms do not quickly resolve with rest 1
• Position changes typically do not provide significant relief 1
• Baker's cysts can extend far into thigh and calf muscles, which may be detected on examination 1

Complications

• Rupture of a Baker's cyst can occur, causing:
  • Sudden calf pain and swelling 1, 5
  • Symptoms that can mimic deep vein thrombosis (DVT) 1, 5
  • Dissemination of fluid into the calf 2
• Rarely, large cysts can cause:
  • Compression of neurovascular structures 6
  • Intermittent claudication due to popliteal artery compression (rare but documented) 6, 7
  • Lower limb ischemia requiring surgical intervention in severe cases 6

Physical Examination Findings

• Visible and palpable swelling in the popliteal fossa, especially with the knee extended 1, 2
• Fluctuant mass that may increase in size with knee extension 2
• Possible limitation in range of motion of the knee joint 2
• In cases of rupture, diffuse calf swelling and tenderness may be present 5
• Large cysts (>5 cm) with disproportionate symptoms should raise suspicion for malignancy 3

Common Associations

• In adults, Baker's cysts are typically associated with underlying knee joint pathology:
  • Meniscal tears 3
  • Osteoarthritis 2, 3
  • Following knee arthroplasty (rare - 0.6% prevalence) 8
• In children, these cysts are often incidental findings without clinical relevance 3

Diagnostic Considerations

• Ultrasound is the preferred initial diagnostic tool to confirm the presence of a Baker's cyst 1, 2, 3
• A ruptured Baker's cyst must be differentiated from DVT, as they can present with similar symptoms 1, 5
• MRI may be used to confirm the diagnosis and evaluate associated intra-articular pathology 5