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.
- 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
- 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.