There is a lump under the skin of the knee that can move and has pain may be a free body of the bone block after trauma, or it may be due to hyperplastic bone, or bursitis, as follows: 1. If the patient has suffered an impact at the knee joint, there may be a patella fracture, and the fragmented fracture block is free in the soft tissue, and there is a localized swelling and pain on pressure. 2. When the patient has degenerative disease of the knee joint, there will be osteophytes around the knee joint, forming a localized bulging mass, which will also show pain when moving or pressing. 3. If the patient’s patella is damaged or repeated friction degeneration, bursa tissue will appear in the patella and the skin, with the continuous extrusion of the movement, the bursa tissue will form a tough mass, and pain symptoms appear during the activity.