**3. Risk factors**


Risk factors for osteonecrosis can be divided into three major groups, summarized in **Table 1**. When no risk factor is identified, osteonecrosis is called "primary."

**Table 1.** Risk factors for "secondary" aseptic osteonecrosis [3].

## **4. Pathological anatomy**

The following four stages of disease progression were identified [4]:

• Stage I: necrosis of bone and bone marrow without evidence of repair

