- Clinical science
Osteonecrosis of the femoral head is a consequence of insufficient vascular supply to the femoral head. Most cases are either idiopathic or associated with alcohol, corticosteroid therapy, or trauma. The condition presents with groin pain, which may radiate to the knee or ipsilateral buttock, and a limited range of motion at the hip. Diagnosis is based on x-ray, followed by MRI. No curative treatments have been identified. Initial nonsurgical treatment focuses on preventing collapse of the femoral head, although surgical intervention may be required if the disease progresses. However, there is no consensus regarding the best treatment options.
For avascular necrosis of the femoral head in children, see “ .”
- Peak incidence: 20–40 years 
Epidemiological data refers to the US, unless otherwise specified.
Though often idiopathic, several traumatic and atraumatic factors may contribute to the development of osteonecrosis.
Atraumatic factors 
- Glucocorticoid use (35–40% of cases)
- Alcohol use disorder (20–40% of cases)
- Hemoglobinopathies (e.g., sickle cell disease)
- Myeloproliferative disorders
- Autoimmune diseases (e.g., SLE, antiphospholipid syndrome)
- Hyperuricemia, hyperlipoproteinemia, diabetes mellitus
- Traumatic factors
Reduced blood supply and bone marrow infarction
- The femoral head is at particular risk of developing avascular necrosis because there is an area of reduced vascularization (watershed zone) between the cranial and caudal parts.
- The foveolar artery is the main artery implicated in avascular necrosis of the femoral head
Diagnosis of osteonecrosis of the femoral head 
X-ray (best initial test)
- Cystic and sclerotic changes in the femoral head
- Subchondral collapse
- Flattening of the femoral head
- MRI (best confirmatory test): used to visualize necrotic-viable bone interface
Staging of osteonecrosis of the femoral head
- Several staging systems have been described. In general, these four important findings are routinely used to formulate a treatment plan:
ARCO staging 
- Stage 0 (initial stage): normal imaging studies but histological evidence of change
- Stage I (reversible early stage): positive MRI but normal x-ray
- Stage II (irreversible early stage): x-ray and MRI are positive but contours are preserved
- Stage III (transitional stage): x-ray shows subchondral fracture
- Stage IV (late stage): x-ray shows flattening of the femoral head
- Stage V: x-ray shows flattening of the femoral head and osteoarthrotic changes (e.g., decreased joint space and acetabular changes)
- Stage VI: x-ray shows complete joint destruction
- No known curative treatment
- Reduce risk factors (e.g., smoking cessation, alcohol abstinence, reduce corticosteroid use if possible)
- Conservative treatment: indicated in early stages of disease to the reduce risk of femoral head collapse but often ineffective 
- Indicated if conservative treatment fails and/or when bone structure is compromised
- Frequently performed in early stages (early surgery improves prognosis)
- Femoral head collapse
- Secondary coxarthrosis
We list the most important complications. The selection is not exhaustive.