It is a common clinical syndrome involving multiple bones in which there is a quantitative reduction of bone tissue mass. These reduction result in the fragile skeleton which is associated with increased risk of fractures, pain or deformity. This condition is particularly common in elderly people and post-menopausal women.

It is classified into two major groups-primary or secondary

Primary-Results from osteopenia without underlying diseases. The exact mechanism is unknown but the result of excessive osteoclastic resorption and bone formation.

It is subdivided into 2:- the idiopathic type found in young & juveniles & less frequent involutional type seen in postmenopausal women and aging individuals.

Secondary– Is attributed to the number of factors (immobilization, anemia, hepatic disease, hyperparathyroidism, starvation, etc.)

Morphologic features:-
Except disuse or immobilization is localized to the affected limb. There is enlargement of medullary cavity & thinning of the cortex.

Histologically-is characterized by active or inactive type.
• Active osteoporosis is characterized by increased bone resorption & formation. Increase in no. of osteoclast, with an increased resorptive surface as well as an increased quantity of osteoid.
• Inactive osteoporosis has minimal bone formation & reduced resorptive activity. Decreased no. of osteoclasts, reduced amount of osteoid which decreased osteoblastic surface.