What is osteonecrosis (ON)?

Osteonecrosis (ON) is a condition where an insufficient supply of blood to the bone results in bone tissue death. With a continued shortage of blood and an ineffective repair process, the bone eventually collapses after tiny breaks (or microfractures) occur. Osteonecrosis is also known as avascular necrosis, aseptic necrosis and ischemic necrosis.

Commonly, ON affects the thigh bone (femur) in the hip area, but can also affect other bones in the body, including the knees, shoulders, ankles and various other joints. (Osteonecrosis of the jaw is a different, unrelated condition.)

Typically, ON will progress, resulting in disability. However, in few cases, it is possible for the bone to heal or be protected from further damage. In these cases there can be few to no symptoms for patients.

What causes ostenecrosis (ON)?

Several risk factors are associated with osteonecrosis. These factors are divided into direct and indirect (less common) risk factors. Direct risk factors for ON include:

  • Trauma
  • Radiation
  • Decompression disease (the “bends” – commonly related to scuba diving)
  • Sickle cell disease

For indirect risk factors, only a small minority of patients (usually under 10%) will get the disease. These include:

Although these factors are known to be associated with ON, the exact cause is still unknown.

What are the symptoms of osteonecrosis (ON)?

Although not all patients will feel symptoms of ON immediately, most will have pain or a loss of motion in the affected joint.

For example:

  • If ON affects the hip, there may be groin pain that spreads down the thigh to the knee.
  • In the knee, the condition can cause pain in the lower end of the thighbone.
  • In the shoulder, ON can result in pain and stiffness in the upper arm.
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