The Popliteal Fossa: A Behind-the-Knee Overview
The popliteal fossa is a diamond-shaped anatomical space located at the back of the knee joint. This region serves as a passageway for various structures moving between the thigh and the lower leg. It is often described as the “knee pit” due to its shallow depression when the knee is extended.
Anatomical Boundaries
The popliteal fossa is defined by specific muscles and bones. Its superior and medial border is formed by the semimembranosus and semitendinosus muscles. Extending superolaterally, the biceps femoris muscle marks the upper outer boundary.
The inferomedial boundary is formed by the medial head of the gastrocnemius muscle. Conversely, the inferolateral boundary is formed by the lateral head of the gastrocnemius muscle. These muscular borders shape the diamond-like appearance of the fossa.
The floor of the popliteal fossa consists of the popliteal surface of the femur and the capsule of the knee joint. The oblique popliteal ligament reinforces the knee capsule in this area, and the popliteus muscle contributes to the floor. The roof is formed by the skin, superficial fascia, and deep popliteal fascia, which is continuous with the fascia lata of the thigh.
Contents and Clinical Significance
Several neurovascular structures traverse the popliteal fossa from the thigh into the leg. The popliteal artery, a continuation of the femoral artery, is the deepest structure and supplies blood to the lower leg. Accompanying it is the popliteal vein, which lies superficial to the artery and drains blood from the lower limb.
The nerves passing through this region are the tibial nerve and the common fibular (peroneal) nerve, both branches of the sciatic nerve. These nerves are the most superficial neurovascular contents. The tibial nerve innervates muscles in the posterior compartment of the leg and foot, and provides sensation to parts of the lower limb. The common fibular nerve also passes through the fossa, winding around the neck of the fibula. Other components include popliteal lymph nodes and adipose tissue.
The popliteal fossa holds clinical importance due to the concentration and superficial position of these structures. Its location makes it vulnerable to various conditions and injuries. A Baker’s cyst, a fluid-filled sac, can develop here. The popliteal artery is also susceptible to aneurysms, which are abnormal bulges in the vessel wall.
Medical professionals use the popliteal fossa for diagnostic and therapeutic procedures. The popliteal pulse, which indicates the circulatory status of the lower limb, is assessed here. Nerve blocks targeting the sciatic nerve branches are performed for pain management during or after surgeries involving the foot or ankle. This type of block provides effective pain relief while allowing patients to retain the ability to flex their knee.