Pain in the left shoulder and rib cage potentially is caused by physical injury, spleen irritation, ulcers, costochondritis and heart complications, according to MedGuidance. A doctor should be consulted when sharp pains are present for any length of time or if there is a known physical injury that has occurred.
Physical trauma can damage the muscles and the bones in the shoulder and the ribs, as well as the organs underneath the rib cage. All these typically cause extreme pain, and a suspected fracture is reason to seek out a physician immediately, per Healthline. The spleen is the most common organ injured from impact to the left rib cage and can cause severe internal bleeding, states WebMD. Pain in the left shoulder further indicates a potential spleen injury, according to MedGuidance.
Ulcers can also originate on the left side and cause referred pain in the left arm and shoulder, states MedGuidance. This pain may only last for a few minutes at a time, or it can come back regularly.
Costochondritis is a condition where the cartilage between the ribs becomes inflamed, making it difficult to move and breathe comfortably. Women and people over 40 are at the highest risk for this type of injury, according to Healthline.