The term compression fracture describes a type of fracture in which a spinal vertebra caves in on itself due to compression—or pressure—on the bone. There are several types of compression fractures, each with different risks and treatment options. The most common cause of a spinal compression fracture is osteoporosis. In vertebrae weakened by osteoporosis, a slight increase in stress, or even just the normal amount of pressure placed on them, can cause them to break. Compression fractures occur most often in the lower portion of the thoracic (middle) spine or in the upper portion of the lumbar (lower) spine, where stressed tend to be highest on the vertebrae.
There are three types of compression fractures: wedge, crush, and burst.
Wedge fracture. A wedge fracture is the most common type of compression fracture. It usually occurs in the front of the cylinder-shaped vertebra, causing the front of the vertebra to collapse but leaving the back of the bone intact, resulting in a wedge shape. A wedge compression fracture is usually a mechanically stable fracture, but can lead to spinal deformity, such as a hunchback posture.
Crush fracture. A crush fracture is characterized by a fracture throughout the entire vertebra, not just the front. In this type of compression fracture, the bone tends to collapse in on itself, and these fractures are usually mechanically stable.
Burst fracture. A burst fracture is aptly named, because as the vertebra collapses, it breaks out in multiple directions, often sending pieces of shattered bone into the surrounding tissues of the spine or the spinal cord. This type of fracture is usually more serious than either a wedge or a crush fracture and more likely to be unstable. A burst fracture usually requires immediate medical attention.
Any of the above fractures can also be classified as stable or unstable:
A stable fracture is one that is unlikely to undergo further changes, creating further damage.
An unstable fracture is one that is likely to change further, possibly damaging nerves and other tissue in the process or creating an unacceptable spinal deformity.