Incomplete or nondisplaced posterior column fracture line (not present in this example).Incomplete or nondisplaced transverse fracture line (not present in this example).The quality of the hip reduction: This requires comparison to the other side but appears congruent in this example.Incarcerated fragments: There are no incarcerated fragments in this example.Marginal impaction: In this example, we see severe impaction along the entire posterior acetabular surface (white arrow).The number of fragments associated with the fracture: In this example, the CT scan demonstrates that the posterior wall fragment indeed involves at least two cortical fragments.Thus, this is a posterosuperior wall variant. In this example, the fracture begins well cephalad to the acetabular roof and extends along the supraacetabular surface approximately half way to the anterior inferior iliac spine (blue arrow). The size of the fragment and the region of the posterior wall involved.With posterior wall fractures, one should always evaluate the CT scan for: In this example, the posterior column is seen to be intact as is the anterior rim.The displaced posterior wall fragment(s) is superimposed on the ilium and thus difficult to see. The iliac oblique radiograph demonstrates the integrity of the posterior column, the iliac wing, and the anterior border of the bone. Certainly, the CT scan will be inspected for incarcerated fragments but the reduction is appropriate at this stage. The femoral head is reduced and comparison to the other side would demonstrate near congruence of the reduction. The anterior column is intact, as is the obturator foramen. In Type 2 dysplasia, the angulation of the roof may be less than 10° but the roof is short, providing less coverage of the femoral head. It appears as a large fragment however, there may be a perforation of the cortex based on this image. An acetabular index or roof angle of less than 10° is normal but more than 10-15° is considered dysplastic with higher risks of instability (see graphic above). One of the main functions of the bony pelvis is to transfer weight from the vertebral column to the ischial tuberosities when sitting and acetabula and lower extremities when standing ( Fig. It extends cranially above the acetabulum. A key reference point in the acetabulum is the cotyloid fossathat is, the central nonarticular aspect of the acetabulum below the acetabular roof. In this example, a large piece involving a small portion of the radiological roof is seen.If the hip has been reduced, the congruence of the reduction should be inspected on this view, and the involvement (or lack thereof) of the acetabular roof should be considered. The integrity of the anterior column and the obturator foramen is evaluated on this view. The obturator oblique radiograph is the best source of information of the size, character, and displacement of the posterior wall fragment because the femoral head and ilium are rotated to allow exposure of the retro- and supraacetabular surfaces.
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