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What to do with a Baker’s cyst…

Baker’s cyst is a common cause of posterior knee pain.  However, there are some other common conditions which can cause posterior knee pain and some pathology which you do not want to miss.

Differential diagnosis:

  • Common site of referred pain – lumbar spine, patellofemoral joint; pain is poorly localized
  • Local structures can also cause pain – popliteus, biceps femoris or gastrocnemius tendinopathy (pain brought on by repetitive acceleration/decelartion activities)
  • Knee effusion and history of recent knee injury – think Baker’s Cyst
  • Do not miss – deep vein thrombosis, peripheral vascular disease, PCL sprain, popliteal artery entrapment syndrome

Baker’s Cyst

  • Synovial fluid filled mass in popliteal fossa.
  • Often an enlarged bursa located beneath the medial gastrocnemius or semimembranosis muscles or both.
  • Can be thought of a chronic knee joint effusion that herniates between the two heads of the gastrocnemius muscle.
  • Often communicates with joint and is due to intra-articular pathology – medial meniscal tear, cartilage degeneration, arthritis, ACL deficiencies. LOOK for the associated pathology if patient symptomatic.
  • Can occur in children – isolated, asymptomatic and resolves spontaneously.

Investigations: MRI is gold standard

Complications: May rupture and can be mistaken for DVT; may cause bruising around medial malleoli if this occurs (crescent sign).

Treatment: Treat underlying cause if symptomatic, aspiration with steroid injection may be useful in short term for symptoms; if asymptomatic – reassure.

Surgery: Rare and not generally advised given risk to other neurovascular structures.

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