Osteoporosis is a disease of the skeleton in which there is insufficient bone in the skeleton to withstand the stresses that you and I might put on it every day. The consequences are that bones are likely to break or fracture.
Fracture is really the only clinical important feature of osteoporosis.
But the groups of individuals who are most at risk are women after the menopause, particular Caucasian or Asian women, and patients who are put on glucocorticoids or steroid therapy. Those constitute the two highest risk populations. Fortunately today we don't have to take a piece of the skeleton out and examine it under the microscope as we used to in the past. There are well-developed techniques called bone densitometry that allow us to measure the skeleton with high degree of accuracy and precision. There are many techniques available.