Over 100 years ago, Hermann Kummell described a clinical condition in which patients sustained a trivial trauma, had essentially asymptomatic period lasting weeks to months, then developed a painful, progressive angular kyphosis. Since then, many post-traumatic delayed kyphosis have been reported as a Kummell's disease. As a radiologic finding of intravertebral cleft sign was related to this delayed collapse, this abnormal gas or fluid signal in the involved vertebral body was considered as a pathognomic sign. However, recent evidences indicate this delayed progressive collapse and kyphosis of the spine is related to osteoporotic spine fracture in many reports. At this point, by defining and reviewing the definition and etiology of Kummell's disease, we have to look into whether Kummell's disease is a distinct or rare pathophysiologic entity or a complicated clinical result of osteoporotic spine fracture. In this review, author tried to clearly define the definition and diagnosis criteria to diagnose Kummell's disease as a complicated osteoporotic spine fracture and review treatment modalities for this complicated clinical condition.