**5. Diagnosis**

When we refer to osteonecrosis in orthopedics, we are actually using the term for circulatory lesions that affect the bone, which would be better called "infarction." Necrosis caused by

In 1915, Phemister described and differentiated histological changes from necrosis caused by

Regardless of the predisposing factor, the cause of osteonecrosis is always the inadequate blood perfusion of the bone [3]. Bone is a rigid and nondistensible tissue. Besides that, subchondral limited collateral circulation on the convex side of articular surfaces and decreased perfusion pressure of all epiphyses, which helps to explain the higher incidence of osteone-

Risk factors for osteonecrosis can be divided into three major groups, summarized in **Table 1**.

Dislocations Surgeries Ionizing radiation Electric injuries Freezing

Alcoholism Medication

Gaucher's disease Sickle cell disease Autoimmune diseases

When no risk factor is identified, osteonecrosis is called "primary."

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

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

infection (septic necrosis) of those caused by circulatory changes (aseptic necrosis).

circulatory injury may be due to

crosis in some regions of the skeleton.

**Physical injury** Fractures

**Lipid metabolism** Hypercortisolism

**Intraosseous hypertension** Dysbarism

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

**4. Pathological anatomy**

**1.** arterial diseases

**3. Risk factors**

**3.** venous obstruction.

**2.** embolism

4 Osteonecrosis

The diagnosis of osteonecrosis is made through clinical presentation and imaging tests.

The clinical history suggestive of osteonecrosis is the acute onset of severe pain in a patient who had no previous symptoms or who had mild chronic pain. Most of the time, there is no history of trauma associated with the onset of pain.

On physical examination, the affected area shows tenderness and edema. In deep joints, such as the shoulder and the hip, this can be difficult to observe. In addition, both active and passive movements of the affected joint are painful.

Among the imaging exams, the most commonly used are simple radiographies (X‐ray), radionuclide scintigraphy (bone scan), and magnetic resonance imaging (MRI). Although bone scan can detect changes well before X‐ray, these two methods can only detect reparative processes. Therefore, they can only diagnose from stage II of the disease. The advantage of MRI is that it can detect early bone marrow changes, still in stage I of the disease [3, 5].
