The acrophysis: a unifying concept for enchondral bone growth and its disorders. I. Normal growth.

In order to discuss and illustrate the common effects on normal and abnormal enchondral bone at the physes and at all other growth plates of the developing child, the term "acrophysis" is proposed. Acrophyses include the growth plates of secondary growth centers including carpals and tarsals and apophyses, and the growth plates at the non-physeal ends of small tubular bones. The last layer of development of both physes and acrophysis is the cartilaginous zone of provisional calcification (ZPC). The enchondral bone abutting the ZPC shares similar properties at physes and acrophyses, including the relatively lucent metaphyseal bands of many normal infants at several weeks of age. The bone-in-bone pattern of the normal vertebral bodies and bands of demineralization of the tarsal bones just under the ZPC are the equivalent of those bands. The growth arrest/recovery lines of metaphyses similarly have equivalent lines in growth centers and other acrophyseal sites. Nearly the same effects can also be anticipated from the relatively similar growth plate at the cartilaginous cap of benign exostoses ("paraphysis"). The companion article will explore abnormalities at acrophyseal sites, including metabolic bone disease and dysplasias.