Purpose or Case Report: In adults, the terms osteopenia and osteoporosis are used to describe different severities of diminished bone density which can result from a variety of causes. The World Health Organization has defined osteopenia as decreased bone density corresponding to a bone densitometry T-score of -1 to -2.5 and osteoporosis as a more severe deficiency (T score > -2.5). However, the etiology usually is not apparent on radiographs of skeletally mature patients. Osteopenia and osteoporosis are used regardless of the etiology of apparent decreased bone density.

In contradistinction to the ambiguity inherent in adult radiographs, in growing children, the distinctly different etiologies and corresponding histopathologic abnormalities that result in diminished radiographic bone density can be differentiated, thanks to clues offered by the open physis. Disorders that manifest as rickets (the equivalent to adult osteomalacia) result from the decreased ability to deposit calcium hydroxyapatite on a normal amount of osteoid. This causes disruption of endochondral ossification at the physis and results in apparent physeal widening with loss of the zone of provisional calcification. Alternatively, disorders that cause osteoporosis result from diminished osteoid available for subsequent mineralization, show prominent zones of provisional calcification, and are without rickets-like changes.

This educational exhibit will begin with a review of the steps of normal endochondral and intramembranous ossification, followed by a discussion of the pathophysiology of osteomalacia and osteoporosis. Upon this foundation, we will illustrate various etiologies that result in either rickets/osteomalacia or osteoporosis. Finally, we will present the imaging clues that lead to a diagnosis and to the corresponding correct terminology. This use of precise language cannot be stressed enough, as it has important clinical implications.
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