Popliteal Fossa

Introduction

Boundaries

• Upper part - popliteal surface of femur
• Middle part - capsule of knee joint (with oblique popliteal ligament)
• Lower part - popliteus muscle covered by its fascia

Diagram

Contents (from superficial to deep)

1. Nerves (most superficial)

• Larger terminal branch of the sciatic nerve
• Enters the fossa from above under the biceps femoris
• Descends vertically through the center of the fossa
• Exits deep to the plantaris margin to enter the posterior compartment of the leg
• In the fossa it gives branches to gastrocnemius, soleus, plantaris, and popliteus

• Smaller terminal branch of sciatic nerve
• Follows the biceps femoris tendon along the lateral margin of the fossa
• Exits by winding around the neck of the fibula into the lateral compartment

2. Popliteal vein (intermediate)

• Formed by union of the anterior and posterior tibial veins at the lower border of the popliteus
• Lies superficial to the popliteal artery
• Receives the small saphenous vein (which pierces the roof)
• Exits superiorly through the adductor hiatus to become the femoral vein

3. Popliteal artery (deepest)

• Continuation of the femoral artery after it passes through the adductor hiatus
• Deepest structure in the fossa - difficult to palpate directly
• Ends at the lower border of popliteus by dividing into anterior and posterior tibial arteries
• Branches in the fossa:
  • Medial and lateral superior genicular arteries
  • Middle genicular artery (pierces the joint capsule to supply cruciate ligaments)
  • Medial and lateral inferior genicular arteries
  • Sural arteries (to the heads of gastrocnemius)

4. Other contents

• Popliteal lymph nodes (4-5 nodes receiving lymphatics from the knee region and from the small saphenous vein territory)
• Fat and areolar tissue
• Small saphenous vein (in the roof/superficial fascia - drains into popliteal vein)
• Posterior cutaneous nerve of the thigh (passes through the roof)

Detailed Neurovascular Diagram (THIEME Atlas)

Popliteal Artery Branches Diagram

Clinical Significance

1. Baker's cyst (Popliteal cyst): A synovial cyst that bulges posteriorly into the popliteal fossa through the capsule. The subtendinous bursa of the medial head of gastrocnemius communicates with the knee joint and can form a Baker's cyst in inflammatory arthritis. Presents as a swelling behind the knee.
2. Popliteal artery aneurysm: Most common peripheral artery aneurysm. The artery is considered aneurysmal at >7 mm diameter. Often associated with aneurysms elsewhere (femoral artery, aorta). Complications are mainly from distal thromboembolism rather than rupture, potentially causing lower limb ischemia. Diagnosed with duplex Doppler ultrasound.
3. Common fibular nerve injury: The nerve is vulnerable as it winds around the fibular neck just at the exit of the fossa. Fracture of the fibular neck or pressure from a plaster cast can cause foot drop (loss of dorsiflexion and eversion).
4. Popliteal artery compression: The rigid popliteal fascia (roof) means that any expanding mass (aneurysm, Baker's cyst, popliteal abscess) compresses the neurovascular contents, which can compromise circulation distal to the knee.
5. Popliteal pulse: The popliteal artery is the deepest structure; it requires firm, deep palpation with the patient prone and the knee slightly flexed. Absence of popliteal pulse is significant in peripheral vascular disease.

• Common fibular nerve (lateral)
• Tibial nerve (medial)
• Popliteal vein (between nerves, superficial to artery)
• Popliteal artery (deepest, medial)