Osteoporosis. Coloured scanning electron micrograph (SEM) of an osteoporotic femur (thigh bone) head. In places the surface of the bone has been eroded to reveal the underlying tissue. Osteoporosis (brittle bone disease) causes a reduction in overall bone mass and an increase in the bone's porosity, making it more brittle and likely to fracture. It commonly affects the elderly and post-menopausal women, who experience a decrease in levels of the hormone oestrogen. It may also develop following injury or infection. Treatment is with hormone replacement therapy (HRT) and drugs that slow the rate of bone loss.