A 28-year-old female presents with a swelling behind the knee. On examination, the popliteal fossa is explored. Which of the following structures forms the medial boundary of the popliteal fossa?

Explanation

## Popliteal Fossa Anatomy The popliteal fossa is a diamond-shaped space on the posterior aspect of the knee. Its boundaries are: **Medial boundary:** Semimembranosus (superiorly) and semitendinosus (superiorly), with the medial head of gastrocnemius forming part of the inferior medial border. **Lateral boundary:** Biceps femoris (superiorly) and the lateral head of gastrocnemius (inferiorly). **Floor:** Popliteus muscle and posterior capsule of knee joint. **Roof:** Skin, fascia, and popliteal fascia. **Key Point:** The semimembranosus and semitendinosus are hamstring muscles that form the superomedial boundary of the popliteal fossa. The semitendinosus is more superficial and medial, while semimembranosus lies deeper. **Clinical Pearl:** The popliteal fossa contains the popliteal artery, vein, and tibial nerve. Swellings in this region (Baker's cysts, aneurysms, lymphadenopathy) are clinically significant.