Applied Anatomy and Clinical Correlations

Pelvic Ring Stability & Trauma - Crash Course Pelvis

• Pelvic Ring: Composed of sacrum & two innominate bones. Posterior arch (sacroiliac joints & strong posterior ligaments) is crucial for stability.
• Key Stabilizing Ligaments:
  • Posterior Sacroiliac Ligaments (strongest, resist vertical shear)
  • Sacrospinous & Sacrotuberous Ligaments (resist external rotation)
  • Symphysis Pubis & ligaments (anterior support)
• Classification (Examples):
  • Young-Burgess: Based on mechanism of injury (e.g., APC - Anteroposterior Compression, LC - Lateral Compression, VS - Vertical Shear).
  • Tile: Based on stability (A: Stable; B: Rotationally unstable, vertically stable; C: Rotationally & vertically unstable).
• Clinical Concerns: Massive hemorrhage (venous > arterial), urogenital injuries, lumbosacral plexus injuries (L5, S1 roots).
• Management: ATLS protocol, pelvic binder/sheet for temporary stabilization, angiography for arterial bleeding.

⭐ Anteroposterior compression (APC) Type III injuries ("open book" pelvis) involve complete posterior ligament disruption and pubic symphysis diastasis > 2.5 cm.

Perineal Tears & Pudendal Block - Ouch & Order Downstairs

• Perineal Tears: Childbirth injury.
  • 1st degree: Skin, vaginal mucosa.
  • 2nd degree: Muscles.
  • 3rd degree: Anal sphincter.
    • 3a: <50% External Anal Sphincter (EAS) thickness.
    • 3b: >50% EAS thickness.
    • 3c: Internal Anal Sphincter (IAS) also torn.
  • 4th degree: Rectal mucosa.
  • 3rd/4th degree repair prevents incontinence.
• Pudendal Nerve Block: Perineal anesthesia.
  • Targets Pudendal nerve (S2-S4). 📌 S2,S3,S4 keep perineum off floor.
  • Landmark: Ischial spine.
  • Uses: Episiotomy, operative delivery, repair.
  • Anesthetizes: Vulva, lower vagina, perineum.

  ⭐ Pudendal block spares uterine contraction pain (T10-L1).

Pelvic Support Defects & Prolapse - Droops & Dynamics

• Weakening of pelvic floor structures (muscles, ligaments, fascia) causing pelvic organ descent.
• Types:
  • Cystocele (bladder), Rectocele (rectum), Enterocele (bowel)
  • Uterine prolapse, Vaginal vault prolapse (post-hysterectomy)
• Risk Factors: Childbirth, aging, ↑ intra-abdominal pressure (obesity, chronic cough), genetics.
• DeLancey's Levels of Support:
  • Level I (Apical): Uterosacral/cardinal lig. Defect → uterine/apical prolapse.
  • Level II (Lateral): Arcus tendineus fasciae pelvis. Defect → cystocele/rectocele.
  • Level III (Distal): Perineal body. Defect → perineal descent.
• Symptoms: Pelvic pressure, bulge, "dragging", urinary/fecal/sexual dysfunction.
• Diagnosis: POP-Q system.

⭐ The uterosacral ligaments are key for Level I (apical) support; their damage is a primary cause of uterine and vaginal vault prolapse.

Pelvic Neurovasculature Clinical Hits - Pelvic Power Lines

• Arteries:
  • Internal Iliac A.: Ant. div (viscera, PPH ligation); Post. div (pelvic wall).
  • Uterine A.: Crosses ureter anteriorly (📌 "Water under bridge"); hysterectomy risk.
  • Ovarian A.: From abdominal aorta; ovarian torsion risk.
  • Pudendal A.: Main perineum supply; accompanies pudendal N.
• Veins:
  • Pelvic Venous Plexuses (e.g., prostatic, uterine): Valveless; Batson's plexus → vertebral mets.
  • Ovarian V.: Right → IVC; Left → Left Renal V. (↑ L-sided varicocele risk).
• Nerves:
  • Pudendal N. (S2,S3,S4): Perineal sensation/motor; nerve block for childbirth; Alcock's canal entrapment.
  • Obturator N. (L2,L3,L4): Adductor muscles; injury in pelvic surgery (e.g., lymphadenectomy) → adductor weakness, medial thigh sensory loss.
  • Sciatic N. (L4-S3): Vulnerable: misplaced IM gluteal injection, posterior hip dislocation.
  • Pelvic Splanchnic Ns. (S2-S4): Parasympathetic innervation; "Nervi Erigentes" for erection.

⭐ Obturator nerve injury during pelvic lymphadenectomy is a known complication, potentially causing adductor muscle weakness and sensory loss over the medial thigh.

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High‑Yield Points - ⚡ Biggest Takeaways

• Pudendal nerve block: Ischial spine is the crucial palpable landmark for anaesthesia.
• Episiotomy: Posterolateral incision preferred to avoid anal sphincter and Bartholin's duct injury.
• Pelvic fractures: High risk of bladder and urethral injuries, especially with anterior arch disruption.
• Uterine prolapse: Caused by weakened pelvic diaphragm (levator ani) and supporting ligaments.
• Benign Prostatic Hyperplasia (BPH): Common cause of urinary outflow obstruction in elderly males.
• Ischioanal abscess: Common infection in the ischioanal fossa, potentially leading to fistula-in-ano.