Innominate Bone Lecture Notes

Jun 28, 2024

Innominate Bone (Hip Bone) Lecture

Context and Basics

  • Innominate bones: Also known as hip bones.
  • Number: Two innominate bones in the body.
  • Formation of Pelvic Girdle: Articulate posteriorly with the sacrum.
  • Alternate Name: Os coxae refers to the region formed by the innominate bones.

Orientation

  • Anterior/Posterior: Pointy part (pubis) points forward (anterior), sacrum at the back (posterior).
  • Medial/Lateral: Acetabulum (where the femur head articulates) faces laterally.

Complex Structure

  • Comparison: More complex than long bones (e.g., femur) and comparable to the complexity of the skull.
  • Three Parts: Ilium, Ischium, and Pubis.

Parts of the Innominate Bone

Ilium

  • Large Top Section.
  • Structures:
    • Iliac Wing/Ala/Fossa: Depressed smooth surface on anterior side.
    • Posterior View: Iliac wing/ala (no fossa).
    • Iliac Crest: Highest part, important for lumbar puncture (L4 level).
    • Four Iliac Spines: Named based on orientation.
      • Anterior superior iliac spine.
      • Anterior inferior iliac spine.
      • Posterior superior iliac spine.
      • Posterior inferior iliac spine.
    • Iliac Tuberosity: Rough area where sacrum articulates.

Ischium

  • Structures:
    • Greater Sciatic Notch: Larger scoop-like notch.
    • Ischial Spine: Between the greater and lesser sciatic notches.
    • Lesser Sciatic Notch: Smaller scoop-like notch.
    • Ischial Tuberosity: Rough bottom surface, part you sit on.
    • Ischial Ramus: Branch extending from the ischium.

Pubis

  • Structures:
    • Pubic Tubercle: Small raised bump.
    • Symphyseal Surface: Flat surface on the pubic bone, forms pubic symphysis when two innominate bones are together.
    • Superior Pubic Ramus: Upper branch.
    • Inferior Pubic Ramus: Lower branch (halfway becomes ischial ramus).

Obturator Foramen

  • Purpose: Hole allowing passage of obturator nerve, artery, and vein.

Acetabulum

  • Location for Femur Articulation: Faces laterally.
  • Structures:
    • Acetabular Notch: Area where the ridge around the acetabulum dips.
    • Acetabular Fossa: Smooth depressed surface inside the acetabulum.

Clinical Relevance

  • Lumbar Puncture:
    • Adult: Performed between L3-L4 or L4-L5 (spinal cord ends at L1-L2).
    • Newborn: Performed between L4-L5 (spinal cord ends at L3).