The sacral ala (wings of the sacrum) are the lateral masses of the sacrum formed by the fused transverse processes and costal elements of S1, forming the broad flat lateral surface of the upper sacrum lateral to the sacral foramina. The iliacus muscle originates from the sacral ala. The sacroiliac joint is formed between the auricular surface of the sacral ala and the ilium. The lumbosacral trunk (L4-L5) crosses the anterior sacral ala.
The sacral ala is the site of sacral alar fractures in lateral compression pelvic ring injuries, where the ala is impacted as the ilium drives against it. In sacroiliac joint fixation and sacropelvic reconstruction, screws are placed through the sacral ala from the posterior iliac crest (iliosacral screws) or from the anterior iliac cortex (anterior sacroiliac screws). The lumbosacral trunk crossing the anterior sacral ala is at risk of injury in high anterior sacroiliac approaches.
Lateral compression force drives the iliac wing into the sacral ala, producing alar fractures that may be impacted (stable) or with neurological injury from sacral foraminal involvement; CT identifies the fracture line and sacral foraminal impingement, with percutaneous iliosacral screw fixation restoring ring stability for displaced fractures.
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