The popliteal fossa or “knee pit” is a depression at the back of the knee. When the knee is fully extended, this area of the anatomy resembles a small bowl nestled into the back of the knee, and as the knee is bent, it folds in on itself. It's very easy to palpate this area of the anatomy and find its boundaries by reaching down and feeling behind the knee, for those who are curious.
This roughly diamond-shaped structure is bordered by a number of muscles of the leg. It houses the popliteal vein and corresponding popliteal artery, along with several lymph nodes and the common peroneal nerve. As people may note if they feel the area, the structure is bordered on either side by tough tendons that are part of the network of structures used to move and bend the legs.
The upper part of the popliteal fossa is bordered by the bottom of the femur, while the bottom extends to the top of the tibia. The rounded depression is in the back of the knee joint. Hitting this point at the right angle can force someone to fall to their knees, as it essentially pushes the knee joint into folding. This trick is sometimes used in martial arts, and may also be used by law enforcement trying to control an unruly suspect.
Injuries to the popliteal fossa are relatively uncommon. The surrounding muscles can sometimes experience small tears that cause pain and inflammation in the joint, which can be an issue. The development of inflammation or a cyst can put pressure on the nerves and blood supply, causing problems in the lower leg. Physical therapists helping people recover from knee injuries may also note some tightness and tenderness in this area that needs to be addressed with massage and gentle stretching to restore freedom of movement to the knee.
Signs that the depression may be experiencing inflammation include pain, tenderness, reddening, and swelling. Icing the area can bring down the inflammation, as can taking anti-inflammatory drugs. If pain persists or becomes worse, it is a good idea for people to consult a medical professional for treatment recommendations; it is possible that surgery, bracing, or other techniques may be needed to address the issue. The knee joint is a common site for injuries, and a knee specialist can provide the highest level of care.