Background: Classification of fractures is crucial in decision making and planning of acetabular surgery. Transverse fractures with secondary vertical fracture lines--which constitute either a large posterio-superior fragment (floating dome) or an inverse T with the posterior ileum attached to the axial skeleton--have not been described in detail in the literature.
Methods: All acetabular fractures at Ullevål University Hospital have been recorded prospectively since 1993 and classified according to Judet/Letournel.
Results: In 10/449 fractures (2%) there was a transverse fracture line through the acetabulum, with an additional vertical fracture line ascending either to the iliac crest or the SI-joint. In 6 of these fractures the vertical line started within the acetabulum, and the posterior part of the ileum with part of the articular surface was attached to the axial skeleton. In 4 fractures the vertical fracture line started posterior to the joint, constituting a very large posterio-superior fragment without any articular surface (a floating dome).
Interpretation: Open reduction and internal fixation of inverse T-fractures and transverse fractures with a floating dome require different surgical approaches. The latter can be treated through a single approach alone, while the inverse T-fracture may require extensile or combined approaches for adequate reduction and fixation.