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Updated: Jun 11 2022

Pelvis Anatomy


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  • 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.
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