Osteology The pelvic ring formed from 2 innominate bones articulate posteriorly with the sacrum and anteriorly through pubis symphysis Each innominate bone is composed of three fused bones: ilium, ischium, and pubis ilium Anterior superior iliac spine (ASIS) Aneterior inferior iliac spine (AIIS) Posterior superior iliac spine (PSIS) iliopectineal eminence - region union between ilium and pubis gluteal pillar the anterior portion of the gluteus medius insertion and thickening of the iliac crest important fixation pathway for fractures of the pelvis sciatic notch ischium pubis Stability no inherent stability of articulations stability comes from ligament complexes Ligament complexes posterior complex sacroiliac ligaments posterior stronger than anterior iliolumbar ligaments transverse process of L4/L5 to posterior ilium anterior complex pubis symphysis a fibrocartilaginous disc between innominate bones pelvic floor complex sacrospinous ligament transversely oriented resists external rotation sacrotuberous ligaments longitudinally oriented resists vertical translation Blood Supply Abdominal aorta bifurcates at L4 into common iliac system external iliac artery courses over the pelvic brim continues as the common femoral artery (distal to the inguinal ligament) internal iliac artery divides distal and posterior near the SI joint into posterior division leads to the iliolumbar artery, lateral sacral artery, and terminates as the superior gluteal artery anterior division leads to the obturator artery and inferior gluteal artery, terminating as the internal pudendal artery Corona mortis vascular anastomosis that connects the external iliac artery (or inferior epigastric artery) and obturator artery encountered during anterior approaches to pelvis (ilioinguinal and modified Stoppa) can result in brisk bleeding with rapid blood loss if not identified and ligated Posterior venous plexus injury in pelvic fractures can account for majority of blood loss Neurologic Lumbosacral plexus L1-S4 nerve roots Lateral femoral cutanous nerve L2-L3 nerve roots deep to inguinal ligament near ASIS Obturator nerve Femoral nerve Sciatic nerve AP pelvis standard radiograph for all trauma patients Inlet view cranial tilt (x-ray tube angle toward head and photons beamed in a caudal direction) beam perpendicular to the S1 end plate Outlet view caudal tilt (x-ray tube angled toward feet and beamed in cranial direction) demonstrates cranial-caudal displacement of the pelvic ring and sacral morphology Judet radiographs pseudo-lateral (oblique) views of the pelvis designed to evaluate the columns and walls of the acetabulum the views are reciprocal, meaning a LEFT iliac-oblique is the same as a RIGHT obturator-oblique iliac-oblique assessment of the ilioischial line of the posterior column, the roof of the acetabulum, the anterior acetabular wall, and Iliac crest obturator-oblique assessment of the iliopectineal line of the anterior column, the posterior acetabular wall, and the obturator foramen CT provides excellent detail of bony anatomy and can confirm pelvic ring/acetabular fractures that are not always visible on plain radiographs.