This condition occurs when a bone's normal blood supply is disrupted. The affected bone cells die and the dead bone weakens. The bone may begin to fracture and collapse, leading to arthritis.
There are two distinct types of this condition. One type, called spontaneous osteonecrosis, almost always affects only one knee. Doctors aren't completely sure what causes it to develop, but it seems to be linked to injury of the knee joint. Spontaneous osteonecrosis of the knee is most common in women who are older than age 55.
The other type is called secondary osteonecrosis. It usually affects both knees. Its cause is unknown, but it is linked to a variety of risk factors. These include corticosteroid use, alcohol abuse, and blood clotting disorders. Secondary osteonecrosis of the knee is most common in women who are younger than age 55.
Symptoms vary depending on the type of osteonecrosis. Spontaneous osteonecrosis typically causes the sudden onset of pain. This pain may be most noticeable during episodes of increased activity. It may occur when bearing weight or when climbing stairs. Pain may also occur at night. Secondary osteonecrosis is often associated with chronic, deep-rooted pain. Both types of osteonecrosis can limit the mobility of the knee joint.
Treatment options may include nonsurgical options such as medications, knee braces, crutches, and the limiting of activities that cause pain. In advanced cases, surgery may be needed to repair or replace the joint.