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

It is classified into two major groups-primary or secondary

Primary-Results from osteopenia with out underlying diseases. Exact mechanism is unknown but result of excessive osteoclastic resorption and bone formation.

It is subdivided into 2:- idiopathic type found in young & juveniles & less frequent involutional type seen in post menopausal woman and aging individual.

Secondary– Is attributed to number of factor(immobilization, anaemia, hepatic disease, hyperparathyroidism, starvation etc.)
Morphologic features:-
Except disuse or immobilization is localized to the affected linb. 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 increased resorptive surface as well as increased quantity of osteoid.
• Inactive osteoporosis has the minimal bone formation & reduced resorptive activity. Decreased no. of osteoclasts, reduced amount of osteoid which decreased osteoblastic surface.