Baker Cysts

Baker cyst: aka popliteal cyst, is an extrusion of synovial fluid from knee joint space into the gastrocnemius/semimembranous bursa. Precipitated by

  1. Increased production in synovial fluid such as during inflammation states or any intra-articular pathology
  2. A communication formation between the joint and bursa

Image result for baker cyst

Primary: or idiopathic, may develop just behind an otherwise healthy knee joint of young people and children;

Secondary: the more common type; due to an underlying problem within the knee which causes too much synovial fluid to be produced within the joint and stretches the joint capsule.

Image result for baker cyst crescent sign

Symptom and signs:

  • Mostly asymptomatic but causes a chronic bulge behind the knee that normally diminishes with flexion(Physical: soft mass in the medial popliteal space noted on knee extension and decreases with flexion)
  • A feeling of tightness behind the knee which may worsen when knee fully flex or extended or during activity
  • Posterior knee pain, swelling, stiffness

Risk factors: Increases synovial fluid production

  • Trauma: cartilage tear(meniscus)
  • Underlying joint disease: osteoarthritis, rheumatoid arthritis

Outcomes and complications:

  1. Treating the probable underlying problem usually provides relief and most resolve spontaneously 
  2. Venous compression: causing lower limb swelling
  3. Dissection into calf: may mimic acute deep vein thrombosis with erythema, edema and positive Homan sign
  4. Rupture: following strenuous exercise, which may cause posterior knee and calf pain, with tenderness and swelling of the calf mimicking thrombophlebitis or acute DVT; Crescent sign(an arc of ecchymosis visible distal to medial malleolus) may be noted

Image result for baker cyst crescent sign

a few differentials to r/o:

  1. Pes anserinus pain syndrome: or aka anserine bursitis, presents with subacute medial knee pain; a well defined area of tenderness over medial tibial plateau below joint line noted
  2. Stress fracture of tibia: progressive pain at shin and focal tenderness of fracture site

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