When an adult breaks their forearm, it is usually both the radius and the ulna that are snapped due to the force. However, if only one bone is broken, it tends to be the ulna. This is because it is located on the outside of the arm, meaning if the arm is injured during activities such as self-defence, it is the outside of the arm that takes the pressure and becomes damaged. An obvious deformity will be visible even if only an ulnar fracture has occurred as both bones rely on each other for support.
