Popliteal Fossa

The popliteal fossa is a unique anatomical feature located behind the knee joint, formed by the lower part of the femur and the upper part of the tibia. This rhomboid-shaped depression is of great clinical importance due to the presence of various structures and their interactions within this region. It’s counterpart in the upper limb is the cubital fossa

Boundaries

The popliteal fossa is demarcated by specific boundaries, which help define its anatomical extent:

Boundary	Structures
Superomedial Boundary	Semitendinosus muscle, Semimembranosus muscle, (supplemented by Gracilis muscle, Sartorius muscle, Adductor Magnus muscle)
Superolateral Boundary	Biceps femoris muscle
Inferomedial Boundary	Gastrocnemius muscle (medial head)
Inferolateral Boundary	Gastrocnemius muscle (lateral head), Plantaris muscle

Roof and Floor

The popliteal fossa has a distinct roof and floor, contributing to its structural integrity:

Roof

• Skin
• Superficial fascia

Floor

• Superiorly: Femur popliteal surface
• Middle: Knee joint capsule and oblique popliteal ligament
• Inferiorly: Popliteal fascia covering the popliteus muscle

Contents

Several vital structures and elements are found within the popliteal fossa, making it a significant area for clinical examination and interventions:

1. Popliteal Artery and Branches: The popliteal artery, a continuation of the femoral artery, runs through the fossa, giving rise to branches that supply the lower leg.

1. Popliteal Vein and Tributaries: The popliteal vein accompanies the popliteal artery, receiving blood from various tributaries and facilitating venous return.
2. Tibial Nerve and Branches: The tibial nerve traverses the popliteal fossa and divides into multiple branches, including the sural nerve, which innervates the posterior calf region.
3. Common Peroneal Nerve and Branches: The common peroneal nerve passes obliquely along the medial border of the biceps femoris muscle, contributing to the innervation of the lower leg.
4. Posterior Cutaneous Nerve of Thigh: This sensory nerve supplies the skin over the posterior thigh.
5. Obturator Nerve (Genicular Branch): The obturator nerve sends a genicular branch that innervates the knee joint.
6. Popliteal Lymph Nodes: These lymph nodes are responsible for filtering and draining lymphatic fluid from the lower limb.
7. Fat: Adipose tissue is present within the popliteal fossa, providing cushioning and support to the surrounding structures.

Clinical Point: Lump in the Popliteal Fossa
Could be due to – baker’s cyst, sebaceous cyst, lipoma, sarcoma, varicosities of the short saphenous vein in the roof of the fossa, popliteal aneurysm., infection secondary to suppuration in the foot, joint effusion, enlarged bursae (esp. those beneath the semimembranosus and the heads of gastrocnemius) or tumour of the lower end of the femur or upper end of the tibia

Arrangement of Structures in the Popliteal Fossa

Understanding the arrangement and relationships between the structures within the popliteal fossa is essential for clinical assessment and interventions:

• Superficial to Deep: The structures in the popliteal fossa are arranged in the following order: Nerves, Veins, Arteries. (NVA)
• Medial to Lateral (Above): In the superior aspect of the fossa, the arrangement is Artery, Vein, Nerve. (AVN)
• Medial to Lateral (Below): In the inferior aspect of the fossa, the arrangement is Nerve, Vein, Artery. (NVA)

It is important to note that the popliteal vessels cross the tibial nerve anteriorly in the middle of the fossa. Additionally, the tibial nerve descends vertically through the fossa, while the popliteal artery runs downward and slightly laterally. The common peroneal nerve follows an oblique course along the medial border of the biceps femoris muscle.

Clinical Point: Baker’s cyst
A synovial fluid pocket that forms behind the knee due to excess synovial fluid being pushed into the synovial bursa behind the gastrocnemius, semitendinosus, and semimembranosus muscles. (Causes – Rheumatoid arthritis, osteoarthritis.)