Bone appears to us as a rigid, firm substance that hardly changes at all. But in a healthy body there is, in fact, a constant balance between a breakdown and building up of bone substance. However, if more bone is broken down than new bone is produced, we lose bone substance. This is when osteoporosis begins. Our bones lose their strength and are more susceptible to fractures.
Damaged vertebral bodies collapse. This leads to permanent deformities such as the typical "dowager's hump", a form of rounded back that is purely attributable to the loss of bone mass. Severe pain in the spine or the breastbone is a danger sign of pathological bone loss. It indicates that one or more vertebral bodies have already broken.