Pelvic Walls and Floor

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Bony Pelvis - Foundation Frame

  • Composition: 2 Hip (innominate) bones (ilium, ischium, pubis), sacrum, coccyx.
  • Articulations:
    • Sacroiliac joints (posteriorly)
    • Pubic symphysis (anteriorly)
  • Pelvic Brim (Linea Terminalis): Sacral promontory & ala, arcuate line (ilium), pectineal line & pubic crest (pubis).
  • Divisions:
    • True (Lesser) Pelvis: Inferior to brim; obstetric canal.
    • False (Greater) Pelvis: Superior to brim; supports abdominal viscera.
  • Key Landmarks: Ischial spines, ischial tuberosities, ASIS, sacral promontory.
  • Pelvic Outlet: Diamond-shaped; bounded by pubic arch, ischial tuberosities, sacrotuberous ligaments, coccyx tip.

⭐ The interspinous diameter (~10.5 cm), distance between ischial spines, is the narrowest transverse diameter of the pelvic cavity, critical for fetal descent.

Anterior and posterior views of bony pelvis

Pelvic Walls - Muscular Containment

  • Lateral Pelvic Wall:

    • Obturator Internus:
      • Origin: Obturator membrane/foramen. Nerve: N. to obturator internus (L5, S1, S2).
      • Obturator fascia: Forms tendinous arch (levator ani origin).
    • Piriformis:
      • Origin: Anterior sacrum. Nerve: Ventral rami S1, S2.
      • Exits via Greater Sciatic Foramen.

      ⭐ Divides Greater Sciatic Foramen; key passage for neurovasculature.

  • Posterior Pelvic Wall:

    • Piriformis (posterolateral).
    • Coccygeus (Ischiococcygeus):
      • Origin: Ischial spine. Insertion: Sacrum/coccyx.
      • Nerve: S3, S4. Forms posterior pelvic diaphragm.
  • Fascia:

    • Parietal Pelvic Fascia: Lines walls (e.g., obturator fascia).
    • Tendinous Arch of Pelvic Fascia: Pubis to ischial spine.

Pelvic floor muscles sagittal view

Pelvic Diaphragm - Inferior Support System

  • Muscular sling forming pelvic floor; vital for visceral support & continence.
  • Composition:
    • Levator Ani: Main component. (Puborectalis, Pubococcygeus, Iliococcygeus - 📌 PCI)
      • Puborectalis: U-sling; maintains anorectal angle (fecal continence).
      • Pubococcygeus: Pubis to coccyx/anococcygeal raphe.
      • Iliococcygeus: Arcus tendineus to coccyx/anococcygeal raphe.
    • Coccygeus (Ischiococcygeus): Ischial spine to sacrum/coccyx.
  • Innervation:
    • Levator Ani: Nerve to levator ani (S3-S4), pudendal n. branches.
    • Coccygeus: S4-S5 branches.
  • Fascia: Superior & inferior diaphragmatic fascia.
  • Hiatuses: Urogenital (anterior), Anal (posterior). Pelvic diaphragm muscles superior view with hiatuses

⭐ Levator ani injury (esp. pubococcygeus/puborectalis) during vaginal delivery is a major cause of pelvic organ prolapse and stress urinary incontinence.

Pelvic Clinical Correlates - Applied Anatomy Insights

Female Pelvic Floor Anatomy and Organ Prolapse

  • Pelvic Floor Dysfunction (PFD):
    • Levator ani/coccygeus weakness → Stress Urinary Incontinence (SUI), Pelvic Organ Prolapse (POP) (cystocele, rectocele, uterine), fecal incontinence.
  • Childbirth Injuries:
    • Levator ani tears (puborectalis/pubococcygeus most vulnerable).
    • Pudendal nerve damage → perineal pain, sensory/motor deficits.
    • Perineal body tears.
  • Pudendal Nerve Block:
    • Anesthesia for perineal procedures; landmark: ischial spine.
  • Pelvic Fractures:
    • High risk to bladder, urethra, rectum, vessels, nerves (sciatic, obturator).
    • Common patterns: lateral compression, AP compression.
  • Ischioanal Abscess:
    • Infection in ischioanal fossa; potential for complex fistulae.
  • Obturator Hernia:
    • Rare; through obturator canal. Howship-Romberg sign (pain/paresthesia medial thigh).

⭐ The most common site of levator ani injury during vaginal delivery is the puborectalis/pubococcygeus muscle.

High‑Yield Points - ⚡ Biggest Takeaways

  • Pelvic diaphragm = Levator ani + Coccygeus; main pelvic floor support.
  • Levator ani parts: Puborectalis, Pubococcygeus, Iliococcygeus.
  • Puborectalis maintains anorectal angle; crucial for fecal continence.
  • Lateral pelvic walls: Obturator internus & Piriformis muscles.
  • Pudendal nerve (S2-S4): chief sensory and motor supply to the perineum.
  • Pelvic floor weakness leads to pelvic organ prolapse & urinary/fecal incontinence.
  • The tendinous arch of levator ani (ATLA) is a key origin for levator ani and an important landmark for pelvic support surgery.

Practice Questions: Pelvic Walls and Floor

Test your understanding with these related questions

Injury to which of the following muscles that forms the deep support of the perineal body causes cystocele, enterocele and urethral descent?

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Flashcards: Pelvic Walls and Floor

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Which structures pass through both greater and lesser sciatic foramen?P: _____I: Internal Pudendal vesselsN: Nerve to obturator internus

TAP TO REVEAL ANSWER

Which structures pass through both greater and lesser sciatic foramen?P: _____I: Internal Pudendal vesselsN: Nerve to obturator internus

Pudendal Nerve

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