Popliteal Fossa

Fig. 6.85 - Popliteal Fossa: (A) Boundaries, (B) Nerves and vessels, (C) Superficial structures. - Gray's Anatomy for Students

Definition

Boundaries

Upper (Superolateral and Superomedial) Margins

Lower (Inferomedial and Inferolateral) Margins

Floor

• The capsule of the knee joint and adjacent surfaces of the femur and tibia (superiorly)
• The popliteus muscle (inferiorly)

Roof

• The deep fascia (popliteal fascia), continuous above with the fascia lata of the thigh and below with the deep fascia of the leg
• Overlying this is the superficial fascia and skin

Contents

1. Nerves (Most Superficial)

• Originates proximal to the fossa as the larger branch of the sciatic nerve
• Enters the region from above, directly under the margin of the biceps femoris
• Descends vertically through the fossa
• Exits deep to the margin of the plantaris muscle to enter the posterior compartment of the leg

• The smaller branch of the sciatic nerve
• Enters the fossa from above alongside the tibial nerve
• Follows the biceps femoris tendon over the lower lateral margin of the popliteal fossa
• Swings around the neck of the fibula and enters the lateral compartment of the leg
• Clinically important: the head of the fibula is a useful landmark to identify it

2. Popliteal Vein

• Lies deep to the tibial nerve, superficial to the popliteal artery
• Travels with the popliteal artery
• Exits the fossa superiorly through the adductor hiatus to become the femoral vein

3. Popliteal Artery (Deepest)

• The continuation of the femoral artery, which passes posteriorly through the adductor hiatus in the adductor magnus muscle to enter the fossa
• Appears on the upper medial side under the margin of the semimembranosus
• Descends obliquely through the fossa alongside the tibial nerve
• Ends just lateral to the midline by dividing into the anterior and posterior tibial arteries (at the lower border of popliteus)
• It is the deepest structure in the fossa - therefore, it is difficult to palpate; however, a pulse can usually be detected by deep palpation near the midline

• Muscular branches to adjacent muscles
• Paired sural arteries - supply the two heads of gastrocnemius
• Geniculate arteries that contribute to the arterial anastomosis (rete) around the knee:
  • Superior medial and superior lateral genicular arteries
  • Middle genicular artery - pierces the joint capsule to supply the cruciate ligaments
  • Inferior medial and inferior lateral genicular arteries

Structures in the Roof (Superficial Fascia)

• Ascends in superficial fascia on the back of the leg from the lateral side of the dorsal venous arch of the foot
• At the back of the knee, it penetrates the deep fascia (roof of the popliteal fossa) to join the popliteal vein

• Descends through the thigh superficial to the hamstrings
• Passes through the roof of the popliteal fossa
• Continues inferiorly with the small saphenous vein to innervate skin on the upper half of the back of the leg

Surface Anatomy & Palpation

Visualizing the Contents of the Popliteal Fossa - Gray's Anatomy for Students

• The tendons of biceps femoris (laterally) and semitendinosus (medially) are palpable and often visible, marking the upper angles of the diamond
• The head of the fibula on the lateral side of the knee is a reliable landmark for identifying the biceps femoris tendon and the common fibular nerve
• The popliteal artery pulse is sought by deep palpation just medial to the midline of the fossa, with the knee slightly flexed

Clinical Correlates

Baker's Cyst (Popliteal Synovial Cyst)

• An enlarged, synovial fluid-filled sac formed by fusion of the semimembranosus bursa with the subtendinous bursa deep to the medial gastrocnemius
• Located in the medial popliteal fossa at the level of the medial posterior femoral condyle
• Commonly secondary to chronic joint inflammation (e.g., rheumatoid arthritis, osteoarthritis) causing increased synovial fluid production; excess fluid flows from the joint through a channel into the fused bursa
• Presents as painful swelling in the back of the knee
• On MRI (T2-weighted), it appears as a bright high-signal area communicating with the joint space

Popliteal Artery Aneurysm

• The artery is considered aneurysmal when its diameter exceeds 7 mm
• Most commonly associated with aneurysms in other large vessels (femoral artery, thoracic/abdominal aorta) - therefore the entire arterial tree must be investigated when one is found
• Tends to thrombose rather than rupture; complications are mainly distal embolization and lower limb ischemia (can lead to amputation in severe cases)
• Diagnosis: Ultrasound with duplex Doppler - demonstrates dilation, confirms/rules out thrombus, and distinguishes from synovial cysts
• Treatment: Surgical repair due to high thromboembolic risk

Common Fibular Nerve Injury

• The nerve is vulnerable as it winds around the neck of the fibula
• Can be damaged by fractures of the fibular neck, prolonged pressure (e.g., crossing legs), or surgical positioning
• Results in foot drop (loss of dorsiflexion and eversion)

Popliteal Nerve Blocks

• The tibial and common fibular nerves can be targeted in the popliteal fossa for regional anesthesia of the lower leg and foot
• Approach from the tibial nerve in the popliteal fossa is also used surgically for nerve repair

Summary Table