PCNA and osteonecrosis: Some animal studies have demonstrated positive results in the application of ESWT on osteonecrosis with a better induction of tissue ingrowth and neovascularization; it is associated with increased expression of angiogenic growth factors, including BMP-2, vessel endothelial growth factor (VEGF), endothelial nitric oxide synthase (eNOS), and proliferating cell nuclear antigen (PCNA), and it promotes cell proliferation and osteogenesis [19–21].