NOS3 and osteonecrosis: Abbreviations: ABCB1 = adenosine triphosphate-binding cassette B1, ANA = antinuclear antibodies, CR2 = complement receptor type 2, ESR = erythrocyte sedimentation rate, ESWT = extracorporeal shockwave therapy, MRI = magnetic resonance imaging, NOS3 = nitric oxide synthase 3, ON = osteonecrosis, SLE = systemic lupus erythematosus, SLEDAI = system lupus erythematosus disease activity index, SNPs = single nucleotide polymorphisms, VEGF = vascular endothelial growth factor.