Pain in the crook of the leg, that is, pain in the popliteal fossa, is usually related to local trauma, popliteal cyst, lymphadenitis and other diseases. 1. Local trauma: when the local trauma, resulting in soft tissue damage, will cause pain in the crook of the leg, after the swelling is reduced, the pain will gradually disappear. 2. Popliteal cyst: if there is a cyst in the popliteal fossa, when the cyst gradually increases in size and presses on the surrounding tissues, there will also be obvious pain. 3. Lymphadenitis: there are lymph nodes in the popliteal fossa, when the lymph nodes are stimulated by inflammation for a long period of time, it is easy to cause inflammatory reaction, which will lead to pain at the bend of the leg. In order to accurately analyze the cause of the pain at the bend of the leg, it is recommended to consult a doctor in time and make diagnosis and analysis through magnetic resonance imaging and X-ray examination under the guidance of a professional doctor.