Avascular Necrosis: Most Common Site
The femoral head is unequivocally the most common site affected by avascular necrosis, accounting for the vast majority of cases and representing 10,000 to 20,000 new symptomatic cases annually in the United States alone. 1
Anatomic Distribution
The femoral head dominates the clinical landscape of avascular necrosis, with epidemiologic data demonstrating its clear predominance. In patients on corticosteroid therapy—one of the most common risk factors—the hip is affected in 68% of cases, followed distantly by the knee (44%), ankle (17%), and shoulder (15%). 1
Complete Hierarchy of Common Sites
According to the 2022 ACR Appropriateness Criteria, the established order of frequency includes 1:
- Femoral head (most common)
- Humeral head
- Tibial metadiaphysis
- Femoral metadiaphysis
- Scaphoid
- Lunate
- Talus
Critical Clinical Implications
Why the Femoral Head Matters Most
The femoral head's predominance carries profound implications for morbidity and mortality:
- Bilateral involvement occurs in 70-80% of nontraumatic cases, meaning when you diagnose one hip, you must image the contralateral side 1
- Epiphyseal osteonecrosis (like the femoral head) leads to subchondral fracture and secondary osteoarthritis, unlike metadiaphyseal involvement which lacks long-term sequelae 1
- Necrotic volume >30% of the femoral head progresses to collapse in 46-83% of cases, compared to <5% progression when volume is <30% 1
Multifocal Disease Pattern
When avascular necrosis affects sites beyond the femoral head (talus, humeral head), it typically represents multifocal osteonecrosis rather than isolated disease 1. This underscores the systemic nature of the underlying pathophysiology—whether from corticosteroids, alcohol, thrombophilia, or other causes.
Practical Recognition Points
The femoral head's vulnerability stems from its terminal vascular anatomy—it represents an end-arterial blood supply with limited collateral circulation, making it exquisitely susceptible to vascular interruption, occlusion, or extravascular compression from lipid hypertrophy 1.
The condition predominantly affects adults in their third to fifth decades of life, making this a disease of relatively young, active individuals where joint preservation has enormous quality-of-life implications 1.
Common Pitfall
Many cases remain vastly underreported and asymptomatic, particularly metadiaphyseal involvement. Recent studies demonstrate that MRI-proven femoral osteonecrosis can be retrospectively identified on CT abdomen/pelvis performed for unrelated indications, suggesting true prevalence far exceeds recognized cases 1.