The spine is made up of strong bones called vertebrae. A vertebra can break, however, just like any other bone in the body. When a vertebra breaks and then collapses, it is called a vertebral compression fracture. Compression fractures happen most commonly in the thoracic spine (the middle portion of the spine). In the worst cases, such fractures and the resulting compression of the spine can put pressure on the spinal cord and nerves, either from the compression itself or from the protrusion of bone into the nerves of the spinal cord.

A compression fracture is a collapse of a vertebra. It may be due to trauma or due to a weakening of the vertebra (compare with burst fracture). This weakening is seen in patients with osteoporosis or osteogenesis imperfecta, lytic lesions from metastatic or primary tumors, or infection. In healthy patients it is most often seen in individuals suffering extreme vertical shocks, such as ejecting from an ejection seat. Seen in lateral views in plain x-ray films, compression fractures of the spine characteristically appear as wedge deformities, with greater loss of height anteriorly than posteriorly and intact pedicles in the anteroposterior view

Source: wiki

The most common type of fracture affecting the spine especially in adults...it is also a common problem in patients with osteoporosis, a condition that causes bone thinning

The spine is made up of strong bones called vertebrae. A vertebra can break, however, just like any other bone in the body. When a vertebra breaks and then collapses, it is called a compression fracture