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Avascular Necrosis and Related Disorders

DEFINITIONS

OSTEOCHONDROSIS: A group of disorders including osteonecrosis, normal variation, or stress/trauma related changes that appear radiographically similar.

OSTEONECROSIS: A.K.A. Avascular necrosis, AVN, Aseptic necrosis, Ischemic necrosis. Death to osseous and marrow components due to a lack of sufficient blood supply. There are two types of osteonecrosis: 1) Epiphyseal infarction and 2) metaphyseal/diaphyseal infarction.

These two types of osteonecroses look nothing alike, radiographically. The metaphyseal infarction (or medullary infarct) most commonly takes place at the metadiaphyseal region of long bones, typically the proximal humerus and tibia, and the distal femur. The radiographic features are described as calcification in a "serpentine" fashion. This type of osteonecrosis is rarely of clinical significance.

Medullary bone infarct of distal femur

Bone infarct of the proximal humerus

The epiphyseal infarction takes place, obviously at the epiphysis, but more specifically at the subarticular cortex. This type of osteonecrosis is the focus of this web site.

The terms osteochondrosis and osteonecrosis often times can cause confusion for students, professors, and practicing doctors. Most likely this confusion stemmed from discoveries of various conditions, originally termed "osteochondrosis", that resulted in an irregular and fragmented radiographic appearance. It was at that time believed that all of these conditions were caused by a deficient blood flow due to one of many causes, which in turn led to necrotic bone, finally resulting in remodeled, irregular and fragmented bone. Now we know that not only can a lack of blood supply lead to this appearance, but also trauma or stress to apophyseal regions (e.g. tibial tubercle or vertebral endplate) and even completely normal ossification may, at times, lead to a irregular or fragmented appearance. Therefore, to group all of these conditions under one heading of osteochondrosis based on exclusively radiographic appearance, not taking into account pathogenesis, etiology, or clinical significance is unrewarding to say the least.

A heterogeneous group of conditions that look similar on the plain film, but may or may not involve avascular necrosis, may or may not be clinically significant, and may at times be completely normal!

While this is a ridiculous statement, further research has led to a refinement of the various diseases that fall under the big umbrella of osteochondrosis.

These different conditions may be grouped into one of three categories that you may note on the left hand portion of this page. They are:

  1. Disorders of true osteonecrosis, either primary or secondary;
  2. Disorders related to abnormal stress or trauma without evidence of true osteonecrosis;
  3. Variations of normal ossification.

Osteonecrosis refers to the death of bone due to a lack of blood supply. This deficiency may be initiated at the arteries, veins, or capillaries as a result of many different possible causes that will eventually compromise the arterial flow.

A fragmented appearance may also be due to abnormal stresses at a tendon insertion, e.g., Osgood Schlatter's and Sinding-Larsen-Johansson diseases, or from stresses on the bone itself, e.g., Scheuermann's disease, without any evidence of loss of blood supply, and therefore can not be accurately termed osteonecrosis.

The last category of "disorders" is actually normal or a variation of normal ossification of certain bones, again without any pathologic evidence of true osteonecrosis. Those bones include the calcaneus, tarsal navicular, and the ischial tuberosity.

 
   
 

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