Final answer:
The fat pad sign, or sail sign, on an elbow radiograph often suggests an occult fracture when the anterior fat pad protrudes away from the humerus, indicating further diagnostic evaluation.
Step-by-step explanation:
The fat pad sign, also known as the sail sign, is a potential finding on elbow radiography which suggests there may be an occult fracture. This radiographic finding appears due to displacement of the fat pads around the elbow joint which is usually caused by an increase in joint fluid or hemorrhage from a fracture that is not visible on X-rays. When the anterior fat pad is visible in a radiograph, it protrudes away from the humerus, resembling a sail. This is often due to a subtle fracture of the radial head or another part of the elbow, and this sign can be an indicator for further diagnostic evaluation or more advanced imaging.