What is the characteristic sign of a radial head fracture?

A radial head fracture typically presents with a characteristic sign known as the positive flat pad sign, also referred to as the "sail sign." This sign is visible on plain X-rays and occurs due to the presence of an effusion in the elbow joint, which causes the anterior fat pad to become displaced and appear more prominent. This appearance can indicate trauma to the elbow, specifically a fracture of the radial head, even in cases where the fracture may not be directly visible on imaging.

Pain in the shoulder is not directly related to a radial head fracture as this injury primarily affects the elbow joint, not the shoulder. Inability to flex the elbow can be a consequence of various elbow injuries, but it isn't a definitive sign of a radial head fracture. Swelling in the wrist is also not indicative of a radial head fracture since any accompanying swelling would most likely be localized around the elbow itself. The positive flat pad sign serves as an important diagnostic tool to help clinicians identify a possible radial head fracture and guide further assessment and management.