Nothing i'm aware of. Osteonecrosis is a poorly understood process. It can be caused by steroids, trauma, vascular insult, alcohol, or be idiopathic. Once it has started, I am not aware of any medications or alternative medicines which arrest the process. There has been some suggestion that bisphosphonates can arrest the process in the case of idiopathic osteonecrosis (perthes), but this is still investigational.
Yes, special cases. In idiopathic osteonecrosis, Ficat stage I or II, familial and acquired thrombophilia (Factor V Leiden, Prothrombin gene mutations, high Factors VIII, XI, high homocysteine, lupus anticoagulant) can cause osteonecrosis, and the progression of the disease can often be halted by anticoagulant therapy, provided there are no contraindications to osteonecrosis.