Kümmell disease is an eponymous name for avascular necrosis of the vertebrae.
Risk factors include:
osteoporosis
corticosteroid use
alcoholism
radiation therapy
Plain film/CT
shows collapse of affected vertebrae
an intravertebral vacuum cleft
MRI
the intravertebral vacuum cleft is usually seen as signal void at all sequences
if intravertebral fluid is present it is low T1 signal on and high T2 signal