What is the most common risk factor for avascular necrosis (AVN) of the hip?

Most Common Risk Factor for Avascular Necrosis of the Hip

Corticosteroid use is the most common risk factor for avascular necrosis (AVN) of the hip, followed by alcohol consumption. 1

Risk Factor Profile for AVN of the Hip

Primary Risk Factors

• Corticosteroid therapy - The leading cause of non-traumatic AVN 2, 1
• Alcohol consumption - Second most common risk factor 2, 1
• Trauma - Particularly femoral neck fractures and hip dislocations 3
  • Delayed reduction of hip dislocation significantly increases AVN risk 3
  • Hip reductions performed after 24 hours have a 21.73% AVN rate versus 4.34% when performed within 6-12 hours 3

Secondary Risk Factors

• Blood disorders
  • Sickle cell disease 1, 4
  • Lymphoma/leukemia 2
  • Other blood dyscrasias 2
• Metabolic conditions
  • Hyperlipidemia/hypercholesterolemia 1, 4
  • Gaucher disease 2
• Immunological factors
  • HIV infection 2, 1
  • Post-transplantation immunosuppression 1
• Other causes
  • Radiation therapy 2, 1
  • Chemotherapy 2
  • Caisson disease (decompression sickness) 2

Pathophysiology of AVN

AVN occurs through three main mechanisms:

1. Vascular interruption - Direct damage to blood vessels
2. Vascular occlusion - Blockage of vessels by fat emboli, sickle cells, or clots
3. Extravascular intraosseous compression - Often from lipid hypertrophy 2

The final common pathway is critical ischemia leading to bone death 5. The disease typically becomes detectable 1-6 months after exposure to high-risk factors like corticosteroids or after femoral neck fracture 5.

Epidemiology and Distribution

• AVN affects adults primarily in their third to fifth decades of life 2
• Approximately 10,000-20,000 new symptomatic cases occur annually in the United States 2
• In non-traumatic cases, femoral head AVN is often bilateral (70%-80%) 2
• Femoral head AVN accounts for approximately 10% of total hip replacements in the US 2
• In patients on long-term steroid therapy, AVN distribution includes:
  • Hip (68%)
  • Knee (44%)
  • Ankle (17%)
  • Shoulder (15%) 2

Clinical Implications

Understanding the risk factors for AVN is crucial for:

1. Early identification of high-risk patients
2. Risk modification - Addressing modifiable factors like corticosteroid use and alcohol consumption
3. Screening protocols - Particularly for asymptomatic patients with multiple risk factors
4. Early intervention - Critical for preventing subchondral collapse, which is the turning point in disease progression 5

AVN is irreversible once established, making prevention and early detection paramount in high-risk individuals 4. The prognosis worsens significantly after subchondral plate fracture, which typically occurs within the first 2 years of disease onset 5.