D. i.e. Fracture of iliac bone with disruption of sacroiliac joint Cresent Fracture, is a type II lateral compression injury that is veically stable (d/ t maintainence of pa of posterior SI ligament, sacrotuberous and sacrospinous ligaments) but rotationally unstable (d/t veical disruption of iliac wing). The fracture extends from posterior iliac crest, passing through iliac wing (just behind gluteal pillar), and may then exit in greater sciatic notch or more commonly may enter the sacroiliac (S I) joint - which is then disrupted inferiorly pretending of as fracture dislocation of SI joint complex. The injury leaves a crescent shaped poion of iliac wing attached to the superior aspect of the sacrum, held in place by stout SI ligament. Lateral compression I are the most common pelvic ring disruption injuries. The fracture often passes through sacral foramina (outlet view) or causing buckling of anterior sacral coex only (best seen on CT or inlet view). These are veically stable and rotationally unstable (to some degree). Lateral compression III occurs when lateral (internally rotating) force compressing one side of ring continues and opens up (externally rotates) the hemipelvis of other side. An internal rotation vector causing sacral or iliac wing compression fracture on one side becomes an external rotation vector on opposite hemipelvis manifesting as paial or complete disruption of SI joint; thus leading to wind swept pelvis appearance. These are rotationally as well as veically unstable (d/t ligamentous injury).