AVN: Pathogenesis


- Discussion: (See: Blood Supply to Femoral Head)
    - there are certain areas of bone in which vascular supply is precarious;
    - these areas are subject to infarction and avascular necrosis;
    - three such regions are head of femur, body of talus, & scaphoid;
    - they have the common feature that a very large portion of their total surface is covered with articular cartilage through which vessels do not penetrate;
    - blood supply for these bones enters through very restricted spaces, & there is limited collateral circulation;
    - when principal route of the circulation to these bones is interrupted by trauma or disease, the collateral circulation is inadequate and necrosis ensues;
    - avascular necrosis occurs in other bones, particularly body of talus, scaphoid, the lunate, and the head of the second metatarsal;
    - occasionally, it develops in multiple areas in the same patient;
    - this condition has been found to be frequent complication of prolonged steroid therapy used in patients with kidney transplants;
    - interference w/ blood supply to femoral head results in infarction that may involve the entire head; more frequently, it is limited to a segment of the head;
    - in infarcted area, there is death of marrow elements & of osteocytes;
    - bone death is recognized histologically by disappearance of osteocytes from their lacunae;
    - following infarction, there is an attempt at revascularization that extends inward from the adjacent viable bone;
    - this revascularization process is very slow in the femoral head;
    - hyperemia of surrounding bones causes osteoporosis of living bone, while infarcted bone retains its density and thus appears whiter or denser on roentgenogram;
    - as vessels approach necrotic area, osteoclastic resorption of dead bone may so weaken the femoral head that a portion of it will collapse, resulting in
             an irregular articular surface that sets the stage for painful degenerative arthritis
    - references:
             - Role of impairment of blood supply of the femoral head in the pathogenesis of idiopathic osteonecrosis.
             - A microangiographic study of idiopathic osteonecrosis of the femoral head.
             - Intraosseous arterial architecture in nontraumatic avascular necrosis of the femoral head. Microangiographic and histologic study.
             - Selective digital subtraction arteriography in necrosis of the femoral head.
             - Intraosseous pressure, oxygenation, and histology in arthrosis and osteonecrosis of the hip.
             - Intra-osseous pressure and oxygen tension in avascular necrosis and osteoarthritis of the hip.


Current concepts on the pathogenesis of osteonecrosis of the femoral head.



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Tuesday, May 22, 2012 9:45 am