Terms

Fracture: interruption of the continuity of part of the skeletal system (=broken bone)
Luxation: dislocation, interruption of the normal interrelation between the components of a joint.

When asked to confirm a fracture, the area in question is always imaged in (at least) 2 different directions. A fracture is generally visible in one direction only. Therefore, never settle for an image in only one direction. If bone fragments are displaced as a result of a fracture, the X-ray beam will not be absorbed by the bone at the fracture site (= the gap) (fig. 1a). This is visible as a lucent line (= black line). Bone fragments may also be compressed (= impacted fracture), causing overlap of bone structures (fig. 1b). In this case there will be increased X-ray absorption at the fracture site, resulting in increased density (= whiter).

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Fracture gap in a proximal humerus fracture and an impacted distal radius fracture.
Fracture gap in a proximal humerus fracture and an impacted distal radius fracture.

Figure 1. Fracture gap in a proximal humerus fracture (a) and impacted distal radius fracture (b).