A 32-year-old male presents to the orthopaedic clinic with a popliteal cyst (Baker's cyst). During clinical examination, the physician palpates the popliteal fossa to assess for associated joint pathology. Which of the following structures forms the medial boundary of the popliteal fossa?

Explanation

## Popliteal Fossa Boundaries The popliteal fossa is a diamond-shaped space located on the posterior aspect of the knee joint. Its boundaries are: **Medial boundary:** Semitendinosus and semimembranosus (superomedial) and medial head of gastrocnemius (inferomedial) **Lateral boundary:** Biceps femoris (superolateral) and lateral head of gastrocnemius (inferolateral) **Floor:** Popliteus muscle, posterior joint capsule, and oblique popliteal ligament **Roof:** Skin, fascia, and semitendinosus aponeurosis ## Key Point: **The medial boundary is formed by the semitendinosus and semimembranosus muscles superiorly**, which are the medial hamstring muscles. Inferiorly, the medial head of gastrocnemius completes the medial boundary. ## Clinical Pearl: Baker's cysts (popliteal cysts) arise from the joint capsule, typically between the medial head of gastrocnemius and semimembranosus. Understanding the anatomy is crucial for clinical examination and ultrasound assessment.