Incomplete disruption of posterior arch, open book injury

Unilateral injuries, rotationally unstable in an external direction, which widens the anterior pelvis (“open book” injury) are classified as AO/OTA 61B2.3 fractures. If the injury is rotationally stable, it is classified as an AO/OTA 61B1.2 fracture.

Posterior injury
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.

Anterior injury
The typical anterior arch injury produced by open book fractures is the 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.