[Physiopathology of osteoporosis (author's transl)].

Osteoporosis is the result of the progressive loss of bone substance which occurs during a lifetime. Its histomorphological characteristics have been well-defined and it appears to be a single entity more particularly related to the general problem of cellular senescence. The rate at which bone is lost can be influenced by many events or general factors, known or unknown, which are capable of accelerating or slowing down its progression. The period when the fracture threshold is passed appears to depend on a bone mass which is weak at the end of the growth period, followed by genetic, mechanical--related more specifically to insufficient muscular activity--, hormonal-hypo-oestrogenemia-factors, and pathological episodes of more rapid demineralization (immobilization, corticotherapy) which become more irreversible with advancing age.