What does small effusion and synovial hypertrophy at the ac joint mean?

I think you: Are reading and MRI report. The acromio-clavicular joint is in the shoulder between the acromion process of the scapula (shoulder blade bone) and the clavicle (collar bone). An effusion is fluid in a joint. Synovium is a lining of a joint. Hypertrophy means that it has become large. In translation, it means you have a slightly damaged shoulder. Follow your doctor's advice.