In clinical practice, there are many conditions that can cause pain in the left back under the rib cage. The most common condition is pain due to direct external force to the left back rib cage, resulting in intercostal muscle injury, lactic acid buildup in the muscle, or intercostal neuritis. In addition, the patient may also experience painful pins and needles at the site of the injury due to a rib fracture caused by an external force to the ribs. This is accompanied by local swelling, subcutaneous bruising, positive local pressure pain, and palpable abnormal activity. In this case, the treatment can be conservative. The patient is instructed to reduce activity and rest in bed. A rib fixation band can be used for immobilization, and an ointment that activates blood circulation and relieves swelling and pain should be applied externally to the injured area. Alternatively, the patient may be instructed to take oral bone-setting medication, which can promote early healing of the fracture end.