Broken arm, X-ray. Coloured X-ray of a fracture (red) at the head of the radius, one of the bones in the human forearm. The radius and ulna bones (white, bottom) articulate with the humerus bone (white, top) of the upper arm at the elbow joint (centre). A radial head fracture can be caused by a fall on an outstretched hand with the elbow extended. A non-displaced fracture like this should mend well after immobilisation for several weeks.