Osteoporosis. Coloured magnetic resonance imaging (MRI) scan of a sagittal section through the spine of a 64 year old patient with osteoporosis. Two of the thoracic vertebrae (purple) have become compressed. This puts pressure on the spinal cord running through the vertebrae, causing pain and possibly paralysis. Osteoporosis is characterised by a loss of bone density and deterioration of bone tissue, and causes pain and immobility. It is most common in post-menopausal women. It may be prevented by a diet rich in calcium, regular weight-bearing exercise and HRT drugs.