Uneven bone density inside the rib cage may be caused by several reasons: 1. It may be caused by old damage to the rib cage. For example, if the patient has had some previous old fractures of the ribs, there may be excessive osteophytes at the fracture end during their recovery. In this case, a plain film will clearly show an uneven density around the fracture end. 2. It may be caused by irregular ossification of the rib cartilage. If the rib cartilage is gradually ossifying due to age, trauma, inflammation, etc., there may be uneven density of rib bone in the process. 3. It may be due to osteoporosis. In patients with osteoporosis, there is often uneven density due to the destruction of rib bone. 4. It may also be caused by bone tumors of the ribs. In the case of such diseases, the uneven density of rib bone may be caused by hyperplasia or necrosis in different areas.