Causes of a spinal cord injury

Spinal cord injury (SCI) involves damage to the nerves within the bony protection of the spinal canal. The most common cause of SCI is trauma, although damage can occur from various diseases acquired at birth or later in life, from tumors, electric shock, poisoning or loss of oxygen related to surgical or underwater mishaps.

A common misconception is that a spinal cord injury means the spinal cord has to be severed in order for a loss of function to occur. In fact, most people who have sustained a SCI, the spinal cord is bruised and intact.

The spinal cord and the brain together make up the central nervous system (CNS). The spinal cord coordinates the body's movement and sensation. Therefore, an injured cord loses the ability to send and receive messages from the brain to the body's systems that control sensory, motor, and autonomic function below the level of injury. Often, this results in some level of paralysis.

Spinal cord injury is an age-old problem, but it wasn't until the 1940s that the prognosis for long-term survival was very optimistic. Prior to World War II, people routinely died of infections to the urinary tract, lungs, or skin. SCI went from a death sentence to a manageable condition. Nowadays, people with spinal cord injury approach the full life span of nondisabled individuals.

Spinal cord trauma is more than a single event. The initial blunt force damages or kills spinal nerve cells. However, in the hours and days after injury a cascade of secondary events, including loss of oxygen and the release of toxic chemicals at the site of injury, further damage the cord.

Acute care following an injury may involve surgery if the spinal cord appears to be compressed by bone, a herniated disk, or a blood clot. Traditionally, surgeons waited for several days to decompress the spinal cord, believing that operating immediately could worsen the outcome. More recently, many surgeons advocate immediate early surgery.

Generally speaking, after the swelling of the spinal cord begins to go down, most people show some functional improvement after an injury.

With many injuries, especially incomplete injuries (some motor or sensory function preserved below the injury level), a person may recover function eighteen months or more after the injury. In some cases, people with SCI regain some function years after the injury.
There is a lot of information and resources to learn about the effects of a spinal cord injury. However, it is important to understand the functions of the spinal cord and its relationship to the brain.

Understanding the spinal cord

The spinal cord includes neurons and long nerve fibers called axons. Axons in the spinal cord carry signals downward from the brain (along descending pathways) and upward toward the brain (along ascending pathways).

Many axons in these pathways are covered by sheaths of an insulating substance called myelin, which gives them a whitish appearance. Therefore, the region in which they lie is called "white matter." Loss of myelin, which can occur with cord trauma and is the hallmark of such diseases as multiple sclerosis, prevents effective transmission of nerve signals.

The nerve cells themselves, with their tree-like branches called dendrites that receive signals from other nerve cells, make up "gray matter." This gray matter lies in a butterfly-shaped region in the center of the spinal cord.

Like the brain, the spinal cord is enclosed in three membranes (meninges):

  • Pia mater: Innermost layer
  • Arachnoid: Delicate middle layer
  • Dura mater: Tougher outer layer.

The spinal cord is organized into segments along its length, noted by their position along the thirty-three vertebrae of the backbone. Nerves from each segment connect to specific regions of the body, and thus control motor and autonomic functions.

In general, the higher in the spinal column an injury occurs, the more function a person will lose.

Cervical region
The segments in the neck, or cervical region, referred to as C1 through C8, control signals to the neck, arms, hands, and, in some cases, the diaphragm. Injuries to this area result in tetraplegia, or as it is more commonly called, quadriplegia.

  • Injury above the C3 level may require a ventilator for the person to breathe.
  • Injury above the C4 level usually means loss of movement and sensation in all four limbs, although often shoulder and neck movement is available to facilitate sip-and-puff devices for mobility, environmental control, and communication.
  • C5 injuries often spare the control of shoulder and biceps, but there is not much control at the wrist or hand. Those at C5 can usually feed themselves and independently handle many activities of daily living.
  • C6 injuries generally allow wrist control, enough to be able to drive adaptive vehicles and handle personal hygiene, but those affected at this level often lack fine hand function.

Thoracic region
Nerves in the thoracic or upper back region (T1 through T12) relay signals to the torso and some parts of the arms.

  • Injuries from T1 to T8 usually affect control of the upper torso, limiting trunk movement as the result of a lack of abdominal muscle control.
  • Lower thoracic injuries (T9 to T12) allow good trunk control and good abdominal muscle control.

Lumbar and sacral regions

  • Those injured in the lumbar, or mid-back region just below the ribs (L1 through L5), are able to control signals to the hips and legs.
  • A person with an L4 injury can often extend the knees.
  • The sacral segments (S1 through S5) lie just below the lumbar segments in the mid-back and control signals to the groin, toes, and some parts of the legs.

Besides a loss of sensation or motor function, injury to the spinal cord leads to other changes, including loss of bowel, bladder, and sexual function, low blood pressure, autonomic dysreflexia (for injuries above T6), deep vein thrombosis, spasticity, and chronic pain.

Other secondary issues related to injury include pressure ulcers, respiratory complications, urinary tract infections, pain, obesity, and depression.

These complications of a spinal cord injury are mainly preventable with good healthcare, diet, and physical activity.

Cells that control spinal cord function

Several types of cells carry out spinal cord functions, including:

  • Large motor neurons have long axons that control skeletal muscles in the neck, torso, and limbs.
  • Sensory neurons called dorsal root ganglion cells, or afferents, carry information from the body into the spinal cord and are found immediately outside the spinal cord.
  • Spinal interneurons, which lie completely within the spinal cord, help integrate sensory information and generate coordinated signals that control muscles.
  • Glia, or supporting cells, far outnumber neurons in the brain and spinal cord and perform many essential functions.
  • One type of glial cell, the oligodendrocyte, creates the myelin sheaths that insulate axons and improve the speed and reliability of nerve signal transmission.
  • Astrocytes, large star-shaped glial cells, regulate the composition of the fluids that surround nerve cells. Some of these cells also form scar tissue after injury.
  • Smaller cells called microglia also become activated in response to injury and help clean up waste products.

All of these glial cells produce substances that support neuron survival and influence axon growth. However, these cells may also impede recovery following injury; some glial cells become reactive and thereby contribute to formation of growth-blocking scar tissue after injury.

Nerve cells of the brain and spinal cord respond to trauma and damage differently than most other cells of the body, including those in the peripheral nervous system (PNS). The brain and spinal cord are confined within bony cavities that protect them, but this also renders them vulnerable to compression damage caused by swelling or forceful injury.

Cells of the CNS have a very high rate of metabolism and rely upon blood glucose for energy – these cells require a full blood supply for healthy functioning; therefore, CNS cells are particularly vulnerable to reductions in blood flow (ischemia).

Other unique features of the CNS are the "blood-brain-barrier" and the "blood-spinal-cord barrier." These barriers, formed by cells lining blood vessels in the CNS, protect nerve cells by restricting entry of potentially harmful substances and cells of the immune system.

Trauma may compromise these barriers, potentially contributing to further damage in the brain and spinal cord. The blood-spinal-cord barrier also prevents entry of some therapeutic drugs.

Complete vs. incomplete SCI

What is the difference between a complete injury and an incomplete injury?

Those with an incomplete injury have some sensory or motor function below the level of injury – the spinal cord was not totally damaged or disrupted. In a complete injury, nerve damage obstructs all signals coming from the brain to the body below the injury.

While there's almost always hope of recovering some function after a spinal cord injury, it is generally true that people with incomplete injuries have a better chance of getting more return.

The sooner muscles start working again, the better the chances are of additional recovery. When muscles come back later, after the first several weeks, they are more likely to be in the arms than in the legs.

As long as there is some improvement and additional muscles recover function, the chances are better that more improvement is possible. The longer there is no improvement, the lower the odds it will start to happen on its own.

SCI stats

A study from the Reeve Foundation estimates that over 1.2 million Americans are living with paralysis resulting from spinal cord injuries – five times the previous commonly used estimate of 250,000.

A sample of the insights gleaned from the research on the prevalence of SCI include:

  • About four out of five people with spinal cord injuries are male.
  • More than half of spinal cord injuries occur in the cervical area, a third occur in the thoracic area, and the remainder occur mostly in the lumbar region.
  • Spinal cord injuries are most commonly caused by motor vehicle accidents, followed by sports-related injuries (more common in children and teenagers), falls and acts of violence.

These findings have major implications for the treatment of spinal cord and paralysis-related diseases – not only for those living with these conditions, but also for their families, caregivers, healthcare providers, and employers.

People who sustain a spinal cord injury are mostly in their teens or twenties, although as the population in general ages, the percentage of older persons with paralysis is increasing.

As the number of people living with paralysis rise and as they age with the injury, the costs associated with treating them increase as well. Each year, paralysis costs the healthcare system billions of dollars. Spinal cord injuries alone cost roughly $40.5 billion annually – a 317 percent increase from costs estimated in 1998 ($9.7 billion).

People living with paralysis and spinal cord injuries are also often unable to afford health insurance that adequately covers the complex secondary or chronic conditions that are commonly linked with paralysis.

Research and scientific developments

Currently, there is no cure for spinal cord injuries. However, ongoing research to test surgical and drug therapies is progressing rapidly. Injury progression prevention drug treatments, decompression surgery, nerve cell transplantation, nerve regeneration, and complex drug therapies are all being examined as a means to overcome the effects of spinal cord injury.

The Reeve Foundation has been leading the charge in spinal cord research for over 30 years, creating a framework to translate scientific breakthroughs into vital new therapies. Additionally, we have established programs to help cultivate the next generation of researchers that will safeguard a pipeline of innovation across the field and speed the delivery of cures for spinal cord injury.

Resources on managing SCI

If you are looking for more information on spinal cord injury or have a specific question, our information specialists are available business weekdays, Monday through Friday, toll-free at 800-539-7309 from 9am to 5pm ET.

Our Peer & Family Support Program also provides individualized support through a national peer-to-peer mentoring program.

Additionally, the Reeve Foundation maintains a SCI fact sheet with resources from trusted Reeve Foundation sources. Check out our repository of fact sheets on hundreds of topics ranging from state resources to secondary complications of paralysis.

We encourage you to also reach out to other SCI support groups and organizations, including:

  • CareCure Community offers discussion forums on research, caregiving, travel, sex and relationships, health, and more.
  • Craig Hospital supports a dedicated nurse to answer non-emergency calls from people with SCI, Monday-Friday. Toll-free 1-800-247-0257 or 303-789-8508.
  • Facing Disability provides information and peer support for people with injuries and their families.
  • Paralyzed Veterans of America (PVA) supports veterans and all citizens with spinal cord injuries and diseases.
  • United Spinal Association (USA) provides expertise, connections and access to resources.
  • SCI Information Network offers information about spinal cord injury, including new injuries, and is home to National Spinal Cord Injury Statistical Center (NSCISC).
  • Spinal Injury 101 is a video series from the Shepherd Center, with backing from the Reeve Foundation and the National Spinal Cord Injury Association.
  • SPINALpedia encourages the spinal cord injury community to motivate each other with insights gained from real-world experiences.

Source: American Association of Neurological Surgeons, Craig Hospital, Christopher & Dana Reeve Foundation, The National Institute of Neurological Disorders and Stroke

This project was supported, in part, by grant number 90PRRC0002, from the U.S. Administration for Community Living, Department of Health and Human Services, Washington, D.C. 20201. Grantees undertaking projects under government sponsorship are encouraged to express freely their findings and conclusions. Points of view or opinions do not, therefore, necessarily represent official Administration for Community Living policy.