Left side rib fork bone refers to the left side of the ribs, the left side of the ribs on the side of the bag may be due to osteochondritis, costochondritis, lipoma and so on. 1. Osteochondritis Dissecans: Inflammation of the periosteum of the left side of the rib cage may be caused by sports injuries, pathogenic infections, diabetes, and so on. The patient will have swelling of bone tissue, congestion and edema at the site of osteochondritis, and pain, so there will be a bag on the left side of the rib cage. 2. Costal chondritis: Acute injury to the left costal cartilage can be caused by heavy lifting, severe twisting or chest compression. It manifests as swelling and enlargement of the rib cartilage area, localized pain, and may have a bag on the left side of the rib cage. 3. Lipoma: it may be related to genetic and fat metabolism abnormalities and other factors, when the lesion site near the left side of the ribs, in will form a benign tumor in the local area, resulting in the patient’s left side of the ribs have a bag. The left side of the ribs on the side of the bag can also be seen in other reasons, it is recommended to timely consult a doctor, follow the doctor’s instructions for relevant examinations, in the doctor’s help to clarify the cause, and targeted treatment or treatment.