This is a good case of both anterior and posterior fat pads. Just seeing a posterior fat pad is abnormal and the anterior fat pad is abnormal when you see the so-called “sail” configuration (or triangle with a flat bottom). These are normal fat pads that reside adjacent to the joint capsule and so when there is a joint effusion, it distends the joint, lifting the anterior fat pad into the “sail” configuration as well as superiorly/posteriorly displacing the posterior fat pad (note: generally you see one OR the other).

So there is a joint effusion. But why? Could it just be an effusion from rheumatoid arthritis or septic joint? Sure. But classically this exam is shown with a history of acute/traumatic pain. We don’t see a fracture here and since we all know that the radial head fracture is by far the most common elbow fracture in an adult (and is COMMONLY radiographically occult), the most correct answer is joint effusion with presumed radial head fracture.

If it was a child you could think supracondylar fracture (which is the most common - and often difficult to see) but that is where you use your anterior humeral line and see that it is normal.

Reference: http://radiopaedia.org/articles/radial-head-fractures