Osteoporosis is condition that features loss of the normal density of bone. Osteoporosis leads to literally abnormally porous bone that is more compressible like a sponge than dense like a brick. This disorder of the skeleton weakens the bone leading to an increase in the risk of breaking bones (bone fracture).

Normal bone is composed of protein collagen and calcium. Osteoporosis depletes both the calcium and the protein from the bone, resulting in either abnormal bone quality or decreased bone density. Bones that are affected by osteoporosis can fracture with only a minor fall or injury that normally would not cause a bone fracture. The fracture can be either in the form of cracking (as in a hip fracture) or collapsing (as in a compression fracture of the vertebrae of the spine). The spine, hips, and wrists are common areas of osteoporosis-related bone fractures, although fractures can also occur in other skeletal areas such as the ribs.

The osteoporosis process can operate silently for decades. Some osteoporosis fractures may escape detection until years later. Patients may not thus be aware of their osteoporosis until suffering a painful fracture.

Then the symptoms are related to the location of the fractures. Fractures of the spine (vertebra) can cause severe "band-like" pain that radiates around from the back to both sides of the body. Over the years, repeated spine fractures can cause chronic back pain as well as loss of height or curving of the spine, which gives the individual a hunched-back appearance.

A fracture that occurs during the course of normal activity is called a stress fracture. For example, some patients with osteoporosis develop stress fractures of the feet while walking or stepping off a curb.

Hip fractures usually occur as a result of a fall. With osteoporosis, hip fractures can occur as a result of trivial accidents. Hip fractures may also be difficult to heal after surgical repair because of poor bone quality.