This Phase 3 study aims at demonstrating the efficacy and safety of PREOB® in the treatment of early stage osteonecrosis of the femoral head. More specifically, the purpose of the study is to demonstrate that core decompression/PREOB® implantation into the necrotic lesion is superior to core decompression/placebo implantation in relieving hip symptoms and halting (or reverting) radiological progression of the disease.