Avascular Necrosis (AVN): Causes, Crescent Sign & Treatment

Avascular Necrosis (AVN)

Avascular Necrosis (Osteonecrosis) is cellular death of bone components due to interruption of blood supply. The bone collapses, leading to destruction of the overlying joint surface.

1. Etiology (ASEPTIC)

• A: Alcohol.
• S: Steroids (Most common non-traumatic cause), SLE.
• E: Embolism (Fat/Nitrogen - Caisson disease).
• P: Perthes disease / Pancreatitis.
• T: Trauma (#1 cause: Femoral neck fracture/Dislocation).
• I: Idiopathic / Infection.
• C: Coagulopathies (Sickle Cell).

2. Ficat and Arlet Staging (Femoral Head)

• Stage I: Normal X-ray. MRI shows edema. (Pre-collapse).
• Stage II: X-ray shows sclerosis/cysts. Head is spherical.
• Stage III: Crescent Sign (Subchondral fracture/collapse). Head is flattened.
• Stage IV: Secondary Osteoarthritis (Joint destruction).

3. Management

• Pre-Collapse (Stage I/II): Core Decompression (Drilling to reduce pressure and stimulate angiogenesis) +/- Bone Grafting.
• Post-Collapse (Stage III/IV): Total Hip Replacement (THR).

25 Practice MCQs

Q1. The most common traumatic cause of AVN hip is:

Answer: A). Tears the retinacular vessels.

Q2. The most sensitive investigation for early AVN (Stage I) is:

Answer: A). Shows marrow edema and "Double Line Sign".

Q3. "Crescent Sign" on X-ray indicates:

Answer: A). The cartilage separates from the dead bone.

Q4. Core Decompression works by:

Answer: A). Used in pre-collapse stages.

Q5. Which drug is a major risk factor for AVN?

Answer: A). Causes fat emboli and osteocyte apoptosis.

Q6. Caisson Disease (Decompression sickness) causes AVN due to:

Answer: A). Divers' disease.

Q7. Ficat and Arlet Stage IV involves:

Answer: A). Joint is destroyed.

Q8. Which bone is most commonly affected by AVN?

Answer: A). Weight bearing + precarious blood supply.

Q9. Bisphosphonates are sometimes used in AVN to:

Answer: A). Prevents resorption of the dead bone until new bone forms.

Q10. Kienbock's Disease is AVN of:

Answer: A). Carpal bone.

Q11. Freiberg's Disease is AVN of:

Answer: A). Common in adolescents.

Q12. Preiser's Disease is AVN of:

Answer: A). Idiopathic AVN.

Q13. Perthes Disease occurs in:

Answer: A). Idiopathic AVN of femoral head in kids.

Q14. "Creeping Substitution" refers to:

Answer: A). The natural healing process (but weakens bone temporarily).

Q15. Vascularized Fibular Grafting is used to:

Answer: A). Head-sparing surgery.

Q16. Sickle Cell Anemia causes AVN by:

Answer: A). Infarction.

Q17. Osteochondritis Dissecans (OCD) is a form of AVN affecting:

Answer: A). Creates loose bodies.

Q18. Gaucher's Disease causes AVN due to:

Answer: A). Lysosomal storage disease.

Q19. "Double Line Sign" on MRI T2 indicates:

Answer: A). Pathognomonic for AVN.

Q20. Alcohol intake increases AVN risk by:

Answer: A). Also fat emboli.

Q21. Once the femoral head collapses (Stage III), the best treatment is:

Answer: A). Joint congruity is lost.

Q22. Does AVN cause fever?

Answer: B). Distinguishes from Septic Arthritis.

Q23. Hass' Disease is AVN of:

Answer: A). Rare.

Q24. Sever's Disease is:

Answer: A). Traction injury in kids.

Q25. Bilateral AVN is common in:

Answer: A). Systemic causes affect both hips (50-80%).