Both hemi-pelves are internally rotated, and the pelvic ring is narrowed anteriorly.
This is classified as an AO/OTA 61B3.2 injury.
Each posterior arch injury will be either:
- Anterior sacral compression fracture (partial)
- Partial sacroiliac joint subluxation or fracture subluxation
- Incomplete posterior iliac ring fracture
The pelvic ring is narrowed anteriorly. The anterior arch injury, which may be unilateral on either side, or bilateral, always includes a set of horizontally oriented fractures. Impaction or overlapping of the anterior injuries is evident, and variable in degree.
Infrequently, marked internal rotation displacement through the pubic symphysis can produce a locked symphysis, with gross narrowing of the pelvic ring.
Another unusual anterior arch injury produced by internal rotation (lateral compression) is the Tilt Fracture. This involves dislocation anteriorly of one pubic bone with symphyseal disruption and anteriorly angulated ramus fractures.