The anterior humeral line is drawn by extending a line along the distal humeral shaft towards the elbow joint. In a normal elbow radiograph, the anterior humeral line should pass through the middle third of the capitellum. In children younger than 4 years of age, however, it is common for the line to pass through the anterior third of the capitellum.

The anterior humeral line is important in the assessment of the elbow radiograph. If the line does not intersect the capitellum in its middle third, there may be a minimally displaced distal humeral fracture, such as a Gartland type I supracondylar fracture. In children younger than 4 years of age, as the anterior humeral line does not reliably pass through the middle third of the capitellum, other findings should be sought out such as the sail sign and the posterior fat pad sign.