This is a observation clinical trial. We are collecting the patients with glucocorticoid. They were divided into the experiment group (with femur head necrosis) and control group (without femur head necrosis).Then, we will analyse the patients' genome with genome-wide association study (GWAS). Our purpose is to find susceptibility loci for glucocorticoid-induced femur head necrosis in the Chinese population.

Inclusion Criteria:

1. Subject has given the written informed consent voluntarily;
2. Male or female between 18~60 years;
3. Candidate is clinically diagnosed as avascular osteonecrosis of the femoral head (ONFH), in reference to the diagnostic criteria set forth by Experts' Consensus on the Diagnosis and Treatment of Osteonecrosis of the Femoral Head in Adults (edition 2012);
4. Patient with history of glucocorticoid therapy, in form of oral, muscular or vascular administration, should have total dose equivalent to ≧2000 mg of Prednisone, and maintain on that dose for ≦3 months.

Exclusion Criteria:

1. Subject is not in conformity with diagnostic criteria for ONFH;
2. Patient has a history of trauma in the lower limbs or pelvis;
3. Prolonged addiction to alcohol;
4. Concurrent with renal failure, organ transplant, graft versus host disease, inflammatory bowel disease, HIV infection or leukemia;
5. Patient with familial idiopathic ONFH;
6. Subject suffers from a fatal disease, with life expectancy < 2 months;
7. Woman of child-bearing potential, who is pregnant, in preparation of pregnancy or breast-feeding during the study period;
8. Other patients deemed ineligible at the discretion of the investigator.

patients coming from the Department of Dermatology Xijing Hospital, Fourth Military Medical University Xi'an, China