There are several general reasons for bulging above the knee. First, tumor, when the synovial membrane of the knee has a tumor or the bone of the knee has a tumor, such as osteosarcoma, then there will be a lump above the knee. At this time, it is hard to touch and not able to move, it is necessary to carry out nuclear magnetic CT examination to further diagnose whether it is a tumor of the bone or a tumor in the joint which leads to the bulge of the knee. Secondly, effusion in the suprapatellar bursa of the knee joint, synovitis of the knee or trauma of the knee joint, there will be bloody or yellowish effusion in the knee, which looks like a bulging bag and is soft to the touch, and the diagnosis should be confirmed by nuclear magnetic examination or arthrocentesis. Third, the free body in the knee joint, in the elderly knee joint degeneration, free body in the knee joint, will also appear in the suprapatellar bursa of the knee large lumps, looks like a bulging bag, to be photographed to further confirm the diagnosis.