The “knee pit” is an informal term for the soft indentation at the back of the knee. This area serves as a pathway for various structures connecting the thigh and lower leg. Understanding its anatomy and contents helps comprehend its function and potential health concerns.
The Popliteal Fossa
The anatomical name for the “knee pit” is the popliteal fossa. This diamond-shaped depression is located at the back of the knee joint. Its boundaries are formed by specific muscles: the semitendinosus and semimembranosus muscles form the upper-inner border, the biceps femoris muscle defines the upper-outer border, and the two heads of the gastrocnemius muscle establish the lower boundaries. The term “popliteal” originates from the Latin word poples, referring to the back of the knee.
Key Anatomical Structures
The popliteal fossa contains important structures, including major blood vessels, nerves, and lymph nodes. The popliteal artery and vein are vessels here; the artery, a continuation of the femoral artery, supplies blood to the lower leg and foot, while the vein returns deoxygenated blood. The popliteal artery is the deepest of the neurovascular structures in this region.
Nerves also pass through this space, primarily the tibial nerve and the common fibular (peroneal) nerve, which are branches of the larger sciatic nerve. The tibial nerve provides motor function to muscles in the posterior leg and sensation to the sole of the foot. The common fibular nerve innervates muscles for foot dorsiflexion and eversion, and provides sensation to parts of the lower leg and foot. Popliteal lymph nodes are also located within the fossa, filtering lymphatic fluid from the lower limb as part of the immune system.
Common Conditions and Discomforts
The popliteal fossa can experience various conditions causing discomfort or pain. A common issue is a Baker’s cyst, also known as a popliteal cyst, a fluid-filled sac that forms behind the knee. These cysts are often linked to underlying knee problems like arthritis or meniscus tears, leading to symptoms such as tightness, swelling, or pain.
Nerve entrapment or compression can occur, affecting the tibial or common fibular nerves. This may result in pain, numbness, or weakness in the lower leg and foot. Less frequently, issues with the popliteal artery may arise, such as a popliteal artery aneurysm, which is a bulge in the artery wall. While often asymptomatic, a popliteal aneurysm can lead to symptoms like pain behind the knee, swelling, or a pulsating feeling. In severe cases, it can cause blood clots that impair blood flow to the leg. Persistent discomfort or swelling in the popliteal fossa warrants medical evaluation to determine the underlying cause and appropriate treatment.