Blood Supply of the Hip

Medial Femoral Circumflex Artery (MFCA)

• Origin: Usually from the Profunda Femoris (posteriorly), but can arise directly from the Common Femoral.
• Course: Winds medially around the femur, passing between the Pectineus and Iliopsoas. It then passes Superior to the Adductor Brevis and Inferior to the Obturator Externus.
• Deep Branch: The main trunk runs deep to the Quadratus Femoris.
• Terminal Branch: Gives off the "Lateral Epiphyseal Artery" (See Retinacular system).

This artery supplies the posterior, superior, and lateral aspects of the head (the weight-bearing zone).

Lateral Femoral Circumflex Artery (LFCA)

• Origin: Profunda Femoris (laterally).
• Course: Runs laterally deep to Sartorius and Rectus Femoris.
• Branches: Ascending (anastomoses with MFCA at base of neck), Transverse (Cruciate anastomosis), Descending (Knee).
• Contribution: Supplies the anterior inferior aspect of the neck via anterior retinacular branches.

Anastomoses with the MFCA at the base of the neck to form the "Extracapsular Arterial Ring of Crock".

Ascending Cervical (Retinacular) Arteries

• Origin: From the Extracapsular Ring.
• Course: Pierce the capsule at the base of the neck. Run primarily OUTSIDE the bone, under the synovial reflection (Retinacula of Weitbrecht).
• Groups:
  1. Posterior-Superior: 2-4 vessels (Branches of MFCA). Large and Critical.
  2. Posterior-Inferior: Branches of MFCA.
  3. Anterior: Branches of LFCA. Smaller.
• Entry: Enter the bone at the articular cartilage margin (subcapital region) to become the intra-osseous supply.

Artery of Ligamentum Teres

• Origin: Posterior branch of the Obturator Artery (or Medial Circumflex).
• Course: Travels within the ligament from the acetabular notch to the fovea.
• Significance:
  • Infants: Vital supply.
  • Children: Variable.
  • Adults: Often patent but supplies only a small area around the fovea. Insufficient to rescue the head if neck vessels are cut.

Sometimes referred to as the "Medial Epiphyseal Artery".

1. Extracapsular Ring

• Location: Base of the Neck.
• Formed by: Anastomosis of MFCA (Posteriorly) and LFCA (Anteriorly).
• Function: The base station. If disrupted (Basicervical fracture), supply fails.

This ring ensures redundancy from both medial and lateral sources.

2. Ascending System (Retinacular)

• Location: Surface of the Neck (Intracapsular).
• Vulnerability: High. Intra-capsular tamponade (hemarthrosis) can compress these vessels even if not torn.
• Fracture: Subcapital fractures almost universally disrupt this system.

The preservation of these vessels is the key to head viability.

3. Subsynovial Intra-articular Ring

• Location: Just below the cartilage junction.
• Function: Entry into bone.

These vessels are end-arteries with no further collaterals.

Garden Classification (Femoral Neck Fractures)

Directly correlates with vascular integrity.

• Grade I (Valgus Impacted): Trabeculae angulated. Minimal displacement. Vessels likely Intact. Risk of AVN is low (less than 15%).
• Grade II (Complete, Undisplaced): Break is complete but anatomical reduced. Vessels Intact/Kinked.
• Grade III (Complete, Partially Displaced): Vessels Tethered/Torn. Posterior retinaculum may still be intact.
• Grade IV (Complete, Fully Displaced): Head is dissociated. Vessels Torn. Risk of AVN is high.

Clinical decision making (Fix vs Replace) is driven by this predicted vascular survival. Caveat: the Garden grade has only moderate interobserver reliability, and many surgeons collapse it to a binary undisplaced vs displaced decision in practice.

Avascular Necrosis (Osteonecrosis)

• Mechanism: Ischemia leads to death of osteocytes (within 12-24 hours).
• Creeping Substitution: The body attempts to revascularize and remodel necrotic bone. New woven bone is laid on dead trabeculae.
• Collapse: If the remodeling phase weakens the structure (resorption exceeds formation), the subchondral bone collapses (Crescent Sign).
• Result: Articular incongruity and secondary OA.

The critical "point of no return" is often debated, but prompt reduction (within 6 hours? 24 hours?) is advocated for young patients.

Why the Hip?

• Retrograde supply (no collaterals).
• Intra-capsular space (can be pressurized).
• High weight-bearing loads (leads to collapse).

Other Sites: Scaphoid, Talus, Humeral Head (all share retrograde characteristics).

Technetium-99m

• Mechanism: Uptake depends on blood flow and osteoblastic activity.
• Cold Spot: Indicates avascularity (early phase).
• Hot Spot: Indicates revascularization/healing (late phase).

Useful to predict head viability post-fracture, but rarely changes acute management.

MRI

• Gold Standard for AVN diagnosis.
• Signs: Serpentine line (demarcation between dead and live fat marrow). Double Line sign on T2.
• Marrow Edema: Precedes collapse.

MRI can detect ischemia within 24-48 hours.

Strategy for Vascular Preservation

• Capsulotomy: In young patients, releasing the capsule (hematoma) is thought to reduce intracapsular pressure and improve flow, though evidence is mixed.
• Anatomic Reduction: Essential to "un-kink" the retinacular vessels.

The concept of "unkinking" the vessels by reduction is the primary rationale for urgent surgery.

Cannulated Screw Fixation

• Goal: Compression without rotation.
• Configuration: Inverted Triangle (One inferior, Two superior).
• Safety:
  • Inferior Screw: Passes through the calcar (dense bone).
  • Posterior-Superior Screw: RISK ZONE. If the threads penetrate the posterior cortex, they catch the lateral epiphyseal vessels.
• Technique: Careful lateral viewing to ensure threads are strictly intracapsular/intra-osseous.

"Not too long, not too posterior."

Surgical Dislocation (Ganz)

• Approach: Trochanteric Flip (Digastic).
• Concept: Dislocates the head ANTERIORLY while preserving the MFCA posteriorly intact with the Obturator Externus/Quadratus Femoris muscle flap.
• Utility: Allows full view of the head/acetabulum without AVN risk (if done correctly).

Demonstrates that the MFCA is tethered to the external rotators.