Soreness in the hamstring behind the knee may be caused by strain, popliteal cyst, osteoarthritis of the knee, lumbar disc herniation and so on. 1. Strain: the leg socket behind the knee may be caused by popliteal strain, especially when stretching the knee joint, it will lead to popliteal muscle excessive pulling caused by muscle damage, the patient mainly manifests as soreness and pain behind the knee, and the pain will be more obvious when stretching the knee joint. 2. Popliteal cyst: when popliteal cyst develops to a certain extent, the hamstring behind the knee joint will have soreness and pain, which is mainly manifested as a localized mass at the back of the knee joint, resulting in localized swelling and pain at the back of the knee joint, especially after exertion, the pain at the back of the knee joint will be more obvious. 3. Osteoarthritis of the knee joint: If the patient suffers from osteoarthritis of the knee joint, it will lead to degenerative changes and cartilage degeneration of the knee joint, which will cause the narrowing of the knee joint and the surrounding gap, accompanied by osteophytes, joint effusion and other phenomena, which will lead to soreness and pain in the hamstrings of the hamstrings behind the knee joint. 4. Lumbar disc herniation: the soreness of the hamstring behind the knee may also be related to lumbar disc herniation, due to the cumulative damage caused by the patient’s sitting posture, physical labor, etc., the patient’s lower limbs will have radiating pain, numbness and other symptoms. It is recommended that patients go to the hospital in time for consultation and symptomatic treatment under the doctor’s examination.