Greenstick fractures occur when the force applied to a bone results in bending of the bone such that the structural integrity of the convex surface is overcome. The fact that the integrity of the cortex has been overcome results in fracture of the convex surface. However, the bending force applied does not break the bone completely and the concave surface of the bent bone remains intact.

This can occur following an angulated longitudinal force applied down the bone (e.g. an indirect trauma following a fall on an outstretched arm), or after a force applied perpendicular to the bone (e.g. a direct blow).

This fracture is very different, and much less common, than the torus fracture that results in buckling of the cortex on the concave side of the bend and an intact concave surface.