Definition
Avascular necrosis is death of subchondral bone due to interruption of blood supply. Progressive structural failure can lead to femoral head collapse and secondary arthritis.
Risk factors
- corticosteroid exposure
- alcohol excess
- trauma, especially femoral neck fracture or hip dislocation
- sickle cell disease
- decompression sickness
- autoimmune disease
- transplantation
- idiopathic disease
Clinical features
- groin pain
- reduced hip motion
- pain with weight bearing
- may be bilateral
Imaging
Plain radiographs
May be normal in early disease. Later features include sclerosis, cystic change, crescent sign, collapse and secondary arthritis.
MRI
Most sensitive investigation for early disease and useful for detecting bilateral involvement.
Management principles
Treatment depends on stage, lesion size, symptoms and collapse.
Pre-collapse
- risk-factor modification
- protected loading in selected cases
- joint-preserving procedures such as core decompression in appropriate patients
Post-collapse
Joint-preserving surgery is less predictable. Arthroplasty is commonly required for symptomatic advanced collapse and arthritis.
Diagram
