Increasing the deformity: If you “increase the deformity”, as below, it relaxes the soft tissue on the concave side. If you then push distally on the “side” of the fragment, enough length can be obtained to reapproximate the ends. This is really only necessary in fractures which occurred in bending! You don’t need to “increase the deformity” in comminuted (compression), oblique, or spiral fractures, there’s nothing to “unlock.”
After the ends are reapproximated, correcting the angulation is easy. The reduction can then be maintained by applying three point bending (below) in the opposite direction as the original deforming force. The intact soft tissue prevents overcorrection.
The cast is therefore molded to apply such a three point bend.
Example in the radius.