A bone protruding from the knee may be a normal bulge or an abnormal bulge, the specific reasons are as follows. 1. Patella: under normal circumstances, the patella is located in front of the knee joint, and it can be observed that the bump in front of the knee joint is generally rounded, which is a physiological normal bump. 2. Arthritis: due to joint degeneration, rheumatism and rheumatoid arthritis caused by joint effusion, synovitis, etc., the patient may appear knee protrusion. 3. Fracture deformity healing: due to poor alignment or premature stress after fracture, it will lead to deformity healing of the fracture, and the patient may feel that the knee protrudes a piece of bone. 4. Bone tumor: benign and malignant tumors of knee joint, such as patellar tumor, osteosarcoma, osteochondroma, patients may feel a bone protruding from the knee. If there is a bone protruding from the knee, especially when there is no or accompanying pain and other symptoms, it is recommended to consult the doctor in time, improve the relevant examination, and perform surgical treatment if necessary.