Osteoporosis is a silent, chronic disease characterized by a progressive loss of calcium from bones, with a subsequent decrease in bone density, or bone mass. The low bone mass of osteoporosis predisposes bones to fracture from minor trauma such as a fall. In advanced cases of osteoporosis, a slight bump to the arm or leg may result in a fracture. The disorder is "silent" because its presence and progression can occur for many years without noticeable symptoms. Osteoporotic fractures can occur in any part of the body with the exception of the skull, but they are most common in the distal forearm (Colles' fracture), in the thoracic and lumbar vertebrae (compression fractures of the spine), and in the hip).
The condition of osteopenia, or bone mass that is simply below normal, does not mean a person has or will develop osteoporosis. However, a diagnosis of osteopenia is an indicator for the possibility as well as the importance of instituting measures to increase bone density and calcium (diet adjustment, calcium supplements, weight-bearing exercises and/or medication). Osteopenia or osteoporosis may be suggested by the interpretation of an X-ray for a fracture or other cause, but it requires a bone density test to establish the diagnosis definitively for correct treatment.