The popliteal region, or “knee pit,” is an anatomical area directly behind the knee joint. This diamond-shaped depression serves as a passageway for structures between the thigh and lower leg. Understanding this region helps comprehend lower limb function and recognize potential health concerns.
Pinpointing the Popliteal Fossa
The popliteal fossa is the hollow at the back of the knee. To locate it, one can slightly bend the knee, which makes the surrounding muscles stand out and deepens the depression. Specific muscles border this area, forming its diamond shape. Above and towards the inner side, the semitendinosus and semimembranosus muscles define its boundary. On the upper and outer side, the biceps femoris muscle forms the edge. Below, the two heads of the gastrocnemius muscle, which are part of the calf, create the lower boundaries, along with the plantaris muscle on the outer lower side. The floor of this fossa is formed by the back surface of the femur, the knee joint capsule, and the popliteus muscle.
Essential Anatomy of the Popliteal Space
Within this space, structures connect the thigh to the leg. The popliteal artery, a continuation of the femoral artery, is the deepest of these neurovascular structures. It carries oxygenated blood down to the lower leg and foot, also providing branches that supply the knee joint.
Closely associated with the artery is the popliteal vein, which lies superficial to the artery and collects deoxygenated blood from the lower leg, returning it towards the heart. Accompanying these vessels are two major nerves, both branches of the sciatic nerve.
The tibial nerve is superficial to the vessels, extending into the posterior leg compartment and providing motor and sensory functions to muscles and skin. The common fibular nerve, also a branch of the sciatic nerve, runs along the outer side of the fossa before winding around the neck of the fibula, controlling muscles involved in foot and toe movement and sensation. The popliteal fossa also contains lymph nodes, part of the immune system.
Common Issues in the Popliteal Region
The popliteal region can be affected by various conditions. A common issue is a Baker’s cyst (popliteal cyst), a fluid-filled sac behind the knee. These cysts result from joint fluid accumulation, often due to underlying knee problems like arthritis or cartilage tears. Symptoms include swelling, stiffness, and pain behind the knee, worsening with activity.
Another condition is a popliteal artery aneurysm, a weakened, bulging section of the artery. An aneurysm can cause pain, throbbing, or swelling behind the knee, risking blood clot formation or rupture that impairs blood flow to the lower leg.
Nerve entrapment or compression can also occur in this area. The common fibular nerve is vulnerable as it travels around the fibular bone, susceptible to injury or compression. Symptoms of nerve entrapment can include numbness, tingling, weakness, or pain in the lower leg and foot, depending on which nerve is affected. These conditions highlight the popliteal fossa’s role in lower limb pathology.