The causes of sudden stabbing pain in the left rib cage include acute intercostal muscle sprain or injury, chronic intercostal muscle strain, and costochondritis, as follows: First, acute intercostal muscle sprain or injury: for example, when doing sports, rotating the spine or twisting the waist, it may suddenly flash to the intercostal muscle, which will cause acute pain in the rib cage area. Second, chronic intercostal muscle strain: for example, long hours of ambulatory work and improper sitting posture, often twisting and sitting, can cause an imbalance in the force of bilateral intercostal muscles, which may cause damage to one side of the intercostal muscles, resulting in stabbing pain in one side of the rib area. Third, costal chondritis: costal chondritis will appear unilateral pain of a single rib.