The spine consists of 24 back bones (vertebrae) plus the tailbone (sacrum). The vertebrae bear most of the body’s weight and thus are under a lot of pressure. Disks of cartilage between each back bone help cushion and protect the bones. The spinal cord is a long, fragile tubelike structure that begins at the end of the brain stem and continues down almost to the bottom of the spine (spinal column). The spinal cord consists of nerves that carry incoming and outgoing messages between the brain and the rest of the body.
Injuries may affect the spinal cord or the roots of the spinal nerves (short branches of the spinal nerves), which pass through the spaces between the vertebrae. The bundle of nerve roots that extend downward from the spinal cord (cauda equina) may also be injured. Injuries of the spinal cord cause nerve damage or dysfunction in one the following ways:
Jarring by a blunt injury (such as a fall or a collision)
Pressure (compression) by broken bones, swelling, or an accumulation of blood (hematoma)
Partial or complete tears (severing)
io‘æBecause the spinal cord is surrounded and protected by the spine, injuries of the spine or its connective tissue (such as disks and ligaments—see Figure: A Herniated Disk) can also injure the spinal cord. Such injuries include the following:
Complete separation (dislocation) of adjacent vertebrae
Partial misalignment (subluxation) of adjacent vertebraef
Loosened ligament attachments (composed of connective tissue) between adjacent vertebrae
Ligaments may be loosened so much that the vertebrae move freely. These injuries are considered unstable. When vertebrae move, they can compress the spinal cord or its blood supply and damage spinal nerve roots. An unstable injury to the spine may not damage the spinal cord immediately. For example, the injury may cause muscle spasms that prevent the vertebrae from moving much. However, after hours or days, muscle spasms may subside, enabling the vertebrae to move freely, which can damage the spinal cord.
Almost all people with a spinal cord injury have an injury to the spine, getting in very easy, since just by slipping on snow people can get injured. However, sometimes children do not (see Spinal Cord Injury in Children).
The most common cause of spinal cord injuries is motor vehicle crashes, accounting for almost half of them. Other causes include falls, sports, work-related accidents, and violence (such as a knife or gunshot wound).
Among older people, falls are the most common cause. Older people are also at higher risk of serious spinal injuries because conditions such as osteoporosis and osteoarthritis (degenerative joint disease) are more common among older people.