Bone is made up of two types of tissue. First there is a protein network which forms the structure for the bone. Secondly, there are calcium salts which are deposited and reinforce the protein network to give the bone its strength.
Osteoporosis is a condition where both the protein network and the calcium salts are deficient. This makes the bone softer. There may be very few symptoms until about one-third of the bone strength is lost. Then pain occurs due to distortion and fracture of the bone. It is usually in the spine, which carries the major weight load. One or more vertebrae of the spine may collapse completely, giving acute pain and later shortening of the spine.