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Avascular Necrosis and Related Disorders

SPINE

Kummell, in 1891, reported a delayed post-traumatic vertebral collapse that occurred weeks or even months after an injury. Many underlying mechanisms have been suggested, however, at the present time the most widely accepted mechanism is osteonecrosis. Affected patients generally are middle-aged or elderly men or women with the interval between the acute traumatic episode and the vertebral collapse varying from days to years. While Kummell's disease may be asymptomatic, progressive angular kyphotic deformity accompanied by local pain and sometimes even spinal cord compression are clinical hallmarks. The typical location is the lower thoracic and upper lumbar vertebral bodies. The classic radiographic finding of collapse and a vacuum cleft within the vertebral body appearing as a transverse radiolucent line in the center of the vertebral body or adjacent to one of its endplates, was not described in the initial case study, however. This vacuum cleft is exaggerated with extension views and is seen on CT scans as well as on MR imaging, on the former as low signal intensity on all pulse sequences. Typically, however, the prolonged supine positioning leads to replacement of the gas by fluid resulting in high signal intensity within the cleft on T2-weighted images. Gas within the vertebral body is not diagnostic of osteonecrosis and rarely gas formation from spinal infection and focal collections of gas within the vertebral body reflecting the presence of Schmorl's nodes, can also be present.


Kummel's Disease


MRI - T1 Weighted

MRI - T2 Weighted

Osteonecrosis due to Sickle Cell Disease

Unlike other etiologies of avascular necrosis, sickle cell disease may cause ischemia where there is abundant vascularity, for example, of the vertebral bodies. The reason for this is due to the altered, "sickle", shaped red blood cells. As they traverse the capillaries, they have a propensity to get "clogged". As with hair in the sink, once a number of sickled cells get hung up in the capillary system, it is easier for more and more to get clogged until an ischemic event occurs. The process results in osteonecrosis of the central portion of the vertebral body endplates. Collapse will eventually occur from the loading forces of weight bearing giving rise to the classic "H-Shaped" vertebral body.


AVN of the vertebral bodies due to sickle cell disease
 
   
 

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