What structures are most commonly injured?
There are two bones in the forearm, the ulna which is a straight thin bone which goes from the elbow to the wrist and forms the axis of rotation of the forearm, and the radius. The radius is thin at one end becoming thicker and stronger towards the wrist. It is slightly bowed to allow it to rotate around the ulna when the forearm is rotated.
To demonstrate this place your forearm flat on a table in front of you with the palm up and the back of the little finger touching the table. Now roll the hand over until it is positioned palm down on the table. Note that the little finger and the elbow are still in much the same position while the thumb has moved from outside to inside. When the forearm rotates, the little finger side where the ulna is forms the axis (spindle) around which the rest of the forearm rotates. We can see that the radius is on the outside of the forearm when it is rolled outwards but crosses over the ulna when the forearm is rotated in.
The radius is bowed to allow this movement to occur. If the bowing is not accurately restored after a fracture the forearm will not rotate correctly and this would limit some important functions of the hand.