Popliteal Fossa Contents
The popliteal fossa is the diamond-shaped space behind the knee joint. Its contents are arranged in a consistent superficial-to-deep sequence, and knowledge of this anatomy is essential for regional anaesthesia (popliteal sciatic block), vascular access, and interpreting posterior knee masses.
✦ The Mnemonic
"Two Capable People Venture Across Lowlands"
Superficial to deep: Tibial nerve, Common peroneal, Popliteal vein, Artery, Lymph nodes
Clinical Breakdown
The fossa has four muscular boundaries: superolaterally biceps femoris; superomedially semimembranosus and semitendinosus; inferolaterally and inferomedially the two heads of gastrocnemius. The floor is the popliteal surface of the femur and the posterior capsule of the knee joint.
The popliteal artery is the deepest content and the most important clinically — it is the continuation of the femoral artery passing through the adductor hiatus, and divides at the lower border of popliteus into the anterior and posterior tibial arteries. It is tethered here, making it vulnerable to injury in posterior knee dislocation (risk of limb-threatening ischaemia requiring urgent surgical intervention).
Baker's cyst (popliteal cyst) is a fluid-filled bursa in the posteromedial popliteal fossa, communicating with the knee joint via a one-way valve between the medial head of gastrocnemius and semimembranosus. It represents synovial fluid under pressure from intra-articular pathology (OA, RA, meniscal tear). Treatment is directed at the underlying cause.
⭐ Clinical Pearl
Common peroneal nerve wraps around the fibular neck and divides into deep and superficial peroneal nerves. It is the most commonly injured nerve at the knee (fractures of fibular head, knee dislocation, plaster cast compression). Injury produces foot drop (loss of dorsiflexion — deep peroneal) and loss of sensation over the dorsum of the foot.