The spine is made up of strong bones called vertebrae. A vertebra can break just like any other bone in the body. When the vertebral body collapses, it is called a vertebral compression fracture. These fractures happen most commonly in the thoracic spine (the middle portion of the spine), particularly in the lower part. Vertebral fractures are usually caused by a condition such as osteoporosis, a very hard fall, or another type of injury.
The vertebral bodies are the round blocks of bone that form the front part of the spinal column. Compression fractures of the spine usually occur at the bottom part of the thoracic spine (T11 and T12) and the first vertebra of the lumbar spine (L1). See anatomy of the spine.
Compression fractures of the spine generally occur from too much pressure on the vertebral body. The fracture occurs when the vertebral body collapses, causing the front part of the vertebral body to become wedge shaped. The bone tissue on the inside of the vertebral body is crushed, or compressed.
This can happen when the spine bends forward at the same time downward pressure builds on the spine. For example, falling to the floor in a sitting position causes the spine to bend and the head to be thrust forward. This posture combined with pressure on the buttocks concentrates pressure on the front part of the spine, the vertebral bodies.
There are several causes of compression fractures. If the vertebra is too weak to hold normal pressure, it may take very little pressure to cause it to collapse. Most healthy bones can withstand pressure, and the spine is able to absorb the shock. However, if the forces are too high, one or more vertebrae may fracture.
Osteoporosis is a common cause of compression fractures in the spine. This disease thins bones, often to the point they become too weak to bear normal pressure. They can eventually collapse during normal activity, leading to a spinal compression fracture. Notably, spinal compression fractures are the most common type of fracture from osteoporosis. Forty percent of all women will have at least one by the time they turn 80 years old.
In severe cases of osteoporosis, actions as simple as bending forward can be enough to cause a "crush fracture" in a vertebra. This type of vertebral fracture causes loss of body height and a humped back (kyphosis), especially in elderly women.
Compression fractures due to trauma can come from a fall, a forceful jump, a car accident, or any event that stresses the spine past its breaking point.
Cancer that spreads to the spine weakens the supportive structure of the spine. Metastasis is a term that refers to the spread of cancer cells into other areas of the body. The bones of the spine are a common place for many types of cancers to spread. The cancer may cause destruction of part of the vertebra, weakening the bone until it collapses.
If the fracture is caused by a sudden, forceful injury, you will probably feel severe pain in your back, legs, and arms. You might also feel weakness or numbness if the fracture injures the nerves of the spine. If the bone collapse is gradual, such as a fracture from bone thinning, the pain will usually be milder. There might not be any pain at all until the bone actually breaks.
In very severe compression fractures, parts of the back of the vertebral body may actually protrude into the spinal canal and put pressure on the spinal cord. Fortunately this is not a common occurrence.