A bone protruding below the knee may be related to bone tumor, degenerative disease, fracture deformity healing and other reasons. 1. Bone tumor: When chronic inflammation stimulates for a long time, it will lead to the growth of bone tumor below the knee, if not controlled, it will lead to the tumor increasing, which will make a piece of bone below the knee bulge. 2. Degenerative diseases: with the increasing age, degenerative diseases will occur in the knee area, resulting in bone proliferation, calcification, and the formation of hard knots in the knee joint, resulting in the phenomenon of a bone protruding from below the knee. 3. Fracture deformity healing: If there is a history of fracture in the knee, it may be due to early weight bearing or other reasons that the bone scab grows in a poor position, causing the fracture to heal deformity, thus leading to the symptom of a bone below the knee. It is recommended to go to the hospital in time to see a bone under the knee, and then actively treat the cause of the problem.