Baker’s cysts – communication between the posterior joint capsule and the gastrocnemius-semimembranosus bursa – are fluid-filled distended synovial-lined lesions arising in the popliteal fossa between the medial gastrocnemius and semimembranosus tendons. They are usually located at or below the joint line.

Here are 3 tips to scan Baker’s cyst (transverse scan)

1. Position the patient prone.
2. Place the transducer transverse over the intersection of the medial gastrocnemius and semimembranosus muscles.
3. Identify the following structures:

• • Semimembranosus muscle: Located superficial to the femur.
  • Semitendinosus muscle: Located on top of the semimembranosus.
  • Sartorius muscle and tendon: Located medial to the semimembranosus.
  • Gracilis muscle: Located on top of the semimembranosus.
  • Medial gastrocnemius muscle: Located lateral to the semimembranosus and semitendinosus.
  • Popliteal artery.

Sonoanatomy

Reverse Ultrasound Anatomy

Comparison of sonoanatomy and reverse ultrasound anatomy of Baker’s cyst (transverse scan).

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