In addition, in the experiment of T-786C-eNOS genotype, smoking and the interaction between smoking and eNOS genotype in 95 patients with ONFH, it was also proved that smoking was an important synergistic risk of osteonecrosis associated with T-786C-eNOS polymorphism, and also provided an important basis for the feasibility of secondary collision theory. The gene discussed is NOS3; the disease is osteonecrosis.