Hamstring pain at the bend of the leg may be caused by hamstring injury, synovial inflammation, knee meniscus injury, etc., as follows: 1, hamstring injury: when doing sports, for example, excessive stretching can easily cause hamstring strain, which is manifested as pain in the bend of the leg, that is, the back of the knee joint; 2, synovial inflammation: for example, too much sports or weight-bearing activities, can be manifested as knee joint This is mainly caused by synovitis, and if it is accompanied by synovial fluid leakage, it can also be accompanied by joint swelling; 3. Meniscal injury: Meniscal injury can be manifested as pain in the medial or lateral space of the knee joint, sometimes accompanied by popping sounds when the knee joint is moving, or even joint interlocking, which can seriously affect joint function.