Suddenly found a bulge in the left back under the shoulder blade without pain, considering bursitis, scapula misalignment, subcutaneous effusion. 1. Bursitis: it is because of chronic strain injury caused by aseptic inflammation of the bursa, if the fluid accumulation is not much and there is no obvious pain, it can be improved gradually through rest. 2. Scapula misalignment: caused by poor posture or trauma, the scapula is deformed and the shoulder joint activity is limited, X-ray can be a clear diagnosis. 3. Subcutaneous effusion: caused by cold or local pressure, a small amount of effusion can be self-absorbed, or you can take hot towel or infrared physiotherapy. Left back shoulder blade suddenly appeared a bulging bag need to go to the hospital to check a clear diagnosis and further treatment.