The spine is constituted by 24 vertebrae and the sacrum. The backbones support most of the body´s weight and therefore are under a lot of pressure. A vertebra consists of a drum-shaped part (the body) in the anterior part, a hole for the spinal cord, and several bony projections (called the apophysis) in the posterior part. Disks of cartilage that are located between the vertebrae act as cushions and protect the bones.

In compression fractures, the body of the vertebra collapses, usually due to excessive pressure. These fractures commonly appear in the middle or in the lower back. They are more frequent in elderly people, usually in those with osteoporosis, which weakens the bone. Occasionally, these fractures appear in people with cancer that has disseminated to the spine and weakened it (called pathological fractures). When the bone is weakened, compression fractures may be caused by a low-intensity force, such as when the person lifts an object, leans forward, gets out of bed, or stumble. Sometimes the person does not remember any event that could have originated the fracture.

Sporadically, compression or other types of vertebral fractures result from high-energy trauma, such as in a traffic accident, a high-altitude fall, or a gunshot wound. In such cases, the spinal cord can also be injured, and the spine can be fractured in more than one area. If the cause was a fall from a considerable height and the person landed on one or both heels, he or she can also have a heel fracture.