Unilateral injuries, rotationally unstable in an external direction, which widens the anterior pelvis (“open book” injury) are classified as AO/OTA 61B2.3 fractures.
The posterior pelvic arch injuries involve either the anterior part of the S-I joint, or fracture of the sacral ala which is wider anteriorly and in contact posteriorly. Rotational instability is present on physical exam and x-rays.
The typical anterior arch injury produced by open book fractures is disruption of the pubic symphysis. Less frequently, fractures of the pubis or rami may occur.
Anterior widening of the pelvis is evident as increased space between the two pubic bones, or fracture surfaces. Fractures are vertically oriented.