There are more causes of left rib protrusion, if there is trauma it may be a localized local rib fracture misalignment or a bone crust protrusion formed during the fracture healing process. In this case, there is usually a clear history of trauma, and the condition can be determined by local X-ray or CT and 3D reconstruction. If there is no clear trauma, it may be a localized pathologic fracture dislocation, or a raised rib tumor, or a localized inflamed and enlarged rib cartilage projection. It is usually seen in middle-aged and elderly people, and can be initially determined by chest X-ray examination. If the left rib protrudes from childhood, it may be a developmental deformity of the bones or a calcium deficiency that causes bead-like changes in the rib cage. Localized soft tissue masses such as lipomas, sebaceous cysts, and lymph nodes may also cause localized protrusions, which can be determined by ultrasound examination.