What causes pain under the left shoulder blade radiating to the side?

Commonly missed: Rib. Several possible causes including pleurisy or lung injury. Should see dr, asap. But the most common cause for pain in this location which is not serious, but is extremely painful is a dysfunctional rib. Md's almost never make this diagnosis, but osteopathic docs who commonly do hands-on diagnosis and treatment, in addition to doing all the other work-up, often find and treat this problem.