[Six generalized and local osteopathies]

The remodeling of bone continues throughout life. It takes place in circumscribed areas called BMU (bone multicellular units), which during the remodeling process becomes BRU (bone remodeling units). The time span of the total remodeling process, the number of BRU and the distance in time between the appearance of these BRU in a given localization are responsible for the maintenance, or the increase or decrease, of bone substance, in particular of the trabecular bone. In bone atrophy, or osteopenia, and its clinical manifestation as osteoporosis there is decoupling of the remodeling process, with diminished bone formation which ultimately leads to perforations of the bone plates in the spongious bone. In Paget's disease of bone precipitate remodeling of bone causes the characteristic deformations. Recently, virus-RNA sequences have been shown in the bone cells, which is circumstantial evidence for a slow virus infection. Hyperphosphatasia is characterized by the same morphological alterations and discussion is currently in progress as to whether it is a congenital, or juvenile, form of Paget's disease. In osteogenesis imperfecta four different types are now distinguished; children affected by the most frequent type survive into adult life. In this condition, increased bone remodeling with insufficient bone formation is observed. In contrast, osteopetrosis, or marble bone disease, is due to an osteoclastic insufficiency and thus inadequate bone resorption. In this osteopathy a decoupling of the remodeling process has to be assumed: it is thought that other, still unknown, factors maintain regular bone formation although there is little or no bone resorption. The osteoclastic insufficiency has now been proven.(ABSTRACT TRUNCATED AT 250 WORDS)