1. Sacroiliac Joint — SUPER HIGH YIELD

What it is

• Synovial joint → between auricular surfaces of ilium and sacrum.
• Very little movement.

Why it matters

• Weight-transfer joint → transmits body weight from L5 → sacrum → ilium.
• Stability = almost 100% ligament-based, not bone-based.

Key ligaments

1. Interosseous sacroiliac ligament
• Strongest ligament of pelvis
• Lies deep, between rough pits of sacrum & ilium → main stabilizer.
2. Posterior sacroiliac ligament
• Superficial continuation of the interosseous ligament.
3. Anterior sacroiliac ligament
• Flat band in front of joint → stronger in females.

Important fact for exams

• Pregnancy → SI ligaments soften → slight sacral rotation helps childbirth.

2. Sacrotuberous & Sacrospinous Ligaments — KNOW THESE!

These two decide pelvic outlet shape, foramen formation, pudendal nerve course, AND pelvic stability.

SACROTUBEROUS ligament

From:

Posterior ilium + sacrum + coccyx

To:

Ischial tuberosity

(continues forward as the falciform process)

Exam tricks

• Forms lower border of lesser sciatic foramen.
• Blends with gluteus maximus origin.
• Pierced by perforating cutaneous nerve.

SACROSPINOUS ligament

From: Side of sacrum & coccyx

To: Ischial spine

Exam trick

• Converts greater sciatic notch → greater sciatic foramen.
• Together with sacrotuberous forms the lesser sciatic foramen.

3. Iliolumbar Ligament — L5 Stabilizer

• Runs from L5 transverse process → iliac crest.
• Prevents L5 from sliding forwards on sacrum.
• KEY stabilizer of lumbosacral junction.

➡️ This is why degeneration = L5 spondylolysis risk increases.

4. Sacrococcygeal Joint — Low but Easy Marks

• A symphysis (secondary cartilaginous joint) between sacrum apex & coccyx base.
• Allows slight flexion/extension (bending of coccyx).

Important fact:

• Ligaments may ossify, especially the lateral sacrococcygeal ligament.

5. Pubic Symphysis — High Yield for Obstetrics

• Secondary cartilaginous joint (fibrocartilage between pubic bones).
• Reinforced by:
• Superior pubic ligament
• Arcuate (inferior) pubic ligament

Exam point

• During parturition → slight separation of pubic bones can occur.
• 2 bony surfaces are covered by Hyaline cartilage, in between them fibrocartilage - together forms INTERPUBIC DISC

SUPER-HIGH-YIELD MCQ POINTS (80% exam questions)

1. Strongest pelvic ligament → Interosseous sacroiliac ligament
2. Ligament preventing L5 slipping forward → Iliolumbar
3. Ligaments forming greater/lesser sciatic foramina →
• Sacrospinous
• Sacrotuberous
4. Ligament that softens in pregnancy → Sacroiliac ligaments
5. Pelvic ligament blending with gluteus maximus → Sacrotuberous
6. Joint with almost no movement → Sacroiliac
7. Joint allowing slight coccygeal flexion → Sacrococcygeal
8. Parturition-related loosening occurs at →
• Sacroiliac joints
• Pubic symphysis

🧠 PELVIC LIGAMENTS & JOINTS — EXAM REFLEX BLOCK

🔑 Sacroiliac Joint (SIJ)

If the stem says:

• Weight transmission pelvis
• Almost immobile joint
• Pregnancy ligament softening

👉 REFLEX ANSWER: SACROILIAC JOINT

Lock-in facts

• Joint type → Synovial
• Function → Weight transfer
• Stability → Ligament-based (not bone)
• Pregnancy → Sacroiliac ligaments soften

🦴 Strongest Pelvic Ligament

If asked:

• Most powerful pelvic stabiliser
• Main ligament of SI joint

👉 REFLEX ANSWER: INTEROSSEOUS SACROILIAC LIGAMENT

Never confuse with

• Posterior SI → superficial
• Anterior SI → weaker

🔁 L5 Slipping Forward Prevention

If the stem says:

• L5 stabilisation
• Lumbosacral junction
• Prevents spondylolisthesis

👉 REFLEX ANSWER: ILIOLUMBAR LIGAMENT

One-line lock

• L5 TP → Iliac crest

🚪 Greater & Lesser Sciatic Foramina

If the question mentions:

• Sciatic notch conversion
• Pudendal nerve pathway
• Pelvic outlet shape

👉 REFLEX ANSWERS (PAIR — never single):

• Sacrospinous
• Sacrotuberous

Individual locks

• Sacrospinous → ischial spine
• Sacrotuberous → ischial tuberosity

🍑 Ligament Blending with Gluteus Maximus

If mentioned:

• Gluteus maximus origin
• Pelvic ligament pierced by nerve

👉 REFLEX ANSWER: SACROTUBEROUS

(Perforating cutaneous nerve pierces it)

🪑 Coccyx Movement

If the stem says:

• Slight flexion/extension
• Pain while sitting
• Joint may ossify

👉 REFLEX ANSWER: SACROCOCCYGEAL JOINT

Lock

• Joint type → Symphysis

👶 Obstetric High-Yield

If pregnancy / labour is mentioned → think loosening

👉 REFLEX ANSWERS (TWO ONLY):

• Sacroiliac joints
• Pubic symphysis

Pubic symphysis lock

• Joint type → Secondary cartilaginous
• Ligaments → Superior + Arcuate

⚠️ EXAM TRAP ZONE (READ THIS ONCE)

• Strongest pelvic ligament ≠ sacrotuberous ❌
• L5 slipping ≠ SI joint ❌
• Sciatic foramina ≠ single ligament ❌
• Pregnancy loosening ≠ sacrococcygeal ❌

🏁 80% SCORE LOCK — FINAL REFLEX LIST

1. Strongest ligament → Interosseous SI
2. L5 stabiliser → Iliolumbar
3. Sciatic foramina → Sacrospinous + Sacrotuberous
4. Pregnancy softening → SI ligaments
5. Gluteus maximus blend → Sacrotuberous
6. Least movement joint → SI joint
7. Coccyx flexion → Sacrococcygeal
8. Labour separation → Pubic symphysis + SI joints