Pain in the left rib cage during inspiration may be related to the following causes: 1. Possible fracture of the rib cage. This is often seen when the patient has suffered a direct violent blow to the rib cage, which then leads to a rib fracture. This type of fracture may cause very severe pain that increases when the patient takes a deep breath. In addition, older patients with osteoporosis may suffer fractures due to very minor external forces. For example, when the patient sneezes, it may cause a fracture, which in turn causes pain. 2. There may be pleural-related lesions. For example, when pleurisy or pleural adhesions occur, there may be pain during deep inspiration. 3. There may be some muscle spasms. This is what the people call a bout of gas, often seen in patients during strenuous activity, the sudden acceleration of breathing, which leads to spasm of the intercostal muscles. At this point, the patient is able to induce pain around the ribs with a deep inspiration.