The defining characteristic of this fracture type is that no part of the joint surface remains attached to the stable proximal part of the iliac wing and axial skeleton, such that it represents a complete articular fracture.
Associated both column fractures are formed by the association of the posterior column and the anterior column fractures.
The anterior column is separated by a fracture, which begins at a variable point on the retroacetabular surface.
The fracture line then travels across the ilium and may exit at any point and defines the anterior fragment:
Type I (left), exiting the iliac crest
Type II (right), exiting the anterior ilium
The anterior column fracture may involve:
Incomplete fracture line not exiting the anterior ilium
Associated fragment of the quadrilateral surface
Most of the acetabular roof stays with the anterior column fragments.
The posterior column is detached cranially by a fracture that begins at a variable point along the posterior border of the bone (A). Most commonly, the fracture line begins about the apex of the greater sciatic notch.
Complexities in the posterior column fragment include:
Extension into the SI joint (B)
Segmental involvement of the posterior column
Associated fractures of the posterior wall (C)
A summary of diagnosing the fracture classification based on x-ray and CT images is presented in section Patient assessment.