Popliteal Fossa

Overview Diagram

Shape and Boundaries

• Floor - formed by the posterior capsule of the knee joint, adjacent surfaces of the femur and tibia, and inferiorly the popliteus muscle
• Roof - deep fascia continuous with fascia lata above and leg fascia below, covered by superficial fascia and skin

Visualizing the Contents

Contents

1. Nerves (most superficial)

• Tibial nerve - descends vertically through the fossa, exits deep to the margin of the plantaris muscle, continues into the posterior compartment of the leg
• Common fibular (peroneal) nerve - exits by following the biceps femoris tendon over the lower lateral margin of the fossa, wraps around the neck of the fibula, and enters the lateral compartment of the leg

2. Popliteal vein

3. Popliteal artery (deepest)

• Enters the fossa through the adductor hiatus from the adductor canal
• Appears on the upper medial side under the margin of semimembranosus
• Descends obliquely with the tibial nerve
• Is the deepest structure in the fossa - difficult to palpate, but a pulse can be detected by deep palpation near the midline
• Terminates at the lower border of the popliteus muscle by dividing into the anterior and posterior tibial arteries

Branches of the Popliteal Artery in the Fossa

1. Medial superior genicular artery
2. Lateral superior genicular artery
3. Middle genicular artery - pierces the joint capsule at the oblique popliteal ligament to supply the cruciate ligaments
4. Medial inferior genicular artery
5. Lateral inferior genicular artery

Roof - Superficial Structures

• Small (short) saphenous vein - ascends from the lateral side of the dorsal venous arch of the foot, runs vertically in superficial fascia up the back of the leg, penetrates the deep fascia forming the roof of the fossa, and joins the popliteal vein
• Posterior cutaneous nerve of the thigh - passes through the roof and descends alongside the small saphenous vein

Neurovascular Order (Lateral to Medial at Mid-fossa)

Clinical Relevance

Baker's Cyst (Popliteal Synovial Cyst)

• An enlarged synovial sac formed by the fusion of the semimembranosus bursa with the subtendinous gastrocnemius bursa
• Located in the medial popliteal fossa at the level of the medial posterior femoral condyle
• Develops secondary to chronic inflammation (e.g., rheumatoid arthritis), which drives excess synovial fluid through a channel into the fused bursa
• Causes painful swelling in the posterior knee
• Best diagnosed with MRI (shows the cyst communicating with the joint as a bright T2 signal) or ultrasound with duplex Doppler

Popliteal Artery Aneurysm

• Defined as diameter > 7 mm
• Often associated with femoral artery or aortic aneurysms - the entire arterial tree must be investigated when one is found
• Complications are mainly thromboembolic (distal embolization, ischemia, possible amputation) rather than rupture
• Managed with surgical repair

Common Fibular Nerve Injury

• The common fibular nerve is vulnerable where it curves around the neck of the fibula, which can be used as a palpable landmark to locate it
• Injury here causes foot drop (loss of dorsiflexion and eversion)

Popliteal Artery Pulse

• Because the artery is the deepest structure, the popliteal pulse requires firm, deep palpation with the knee slightly flexed, pressing near the midline of the fossa

• Gray's Anatomy for Students, pp. 720-722
• THIEME Atlas of Anatomy: General Anatomy and Musculoskeletal System