Progression of osteoporosis. Computer artwork showing the progression of osteoporosis of the back over 4 years. Osteoporosis is a condition in which bone density is reduced, weakening the bones and making them susceptible to fractures. Weakening of the vertebrae (blocks) of the spine can cause them to collapse (compression fractures, red blocks), which leads to pronounced forward curvature of the spine. This causes back pain, a reduction in height and reduced mobility. Osteoporosis is most common in post-menopausal women.