The fossa behind the knee is also clinically called the popliteal fossa, and there are several causes of popliteal pain: 1, caused by trauma, when the knee joint strains, sprains, smashes will appear after the surrounding soft tissue damage, popliteal fossa in the back of the knee joint, once this part of the soft tissue damage will lead to pain, when walking there will be increased pain. 2, popliteal pain may be related to popliteal cysts and the formation of popliteal fossa The pain in the popliteal fossa can also be caused by skin infections or insect bites, skin infections often appear as boils, and bites from bees or other poisonous insects can cause pain in the popliteal fossa, which can be clearly diagnosed through local examination.