Health

It is possible to break the bones (vertebrae) of the neck and back without resulting in damage to the spinal cord. Spinal Cord Injury (SCI) exists when there is any damage to the spinal cord itself. Spinal cord injuries can be described as either traumatic or non-traumatic.  

Traumatic spinal cord injury occurs after a blow or powerful force to the spine, which often causes excessive movement of the bones of the spine (vertebrae) because of broken vertebrae or ligament tear. This breakdown of the supporting structures of the spine can cause compression of the spinal cord, altering its normal function. Traumatic spinal cord injury caused by compression of the spinal cord can occur because of a fracture (broken bone) of the vertebra, which results in failure of the protective spinal column where the spinal cord lives. This fracture allows excessive movement of the spine and subsequent direct injury to the spinal cord.  

There are times when a spinal cord injury occurs with no breakage of the vertebrae or spinal column. This can happen if there is a tear or separation of the ligament that connects each vertebra to one another. This can be likened to a railroad train. The boxcar itself is the vertebra and the connection between the boxcars is the ligament. If the connection between the boxcars is released, then the once solid one-piece train is now in two separate pieces and can move in different directions. When a ligament is torn between vertebrae, a similar condition exists. The spinal column above the ligament tear moves in a different direction from that below the ligament tear. The vertebra can then move into the spinal cord and cause injury because of direct compression.

It is possible for a traumatic spinal cord injury to occur without vertebral fracture  or ligament tear. Some individuals are born with a smaller hole through the vertebrae, which gives the spinal cord less room to move. This narrowing is referred to as stenosis. This smaller hole in the vertebrae can also occur as individuals age because of arthritis. This type of wear-and-tear arthritis causes extra build-up of bone on the inside of the hole of the vertebra, narrowing the area where the spinal cord lives. In this condition a normal bending or flexing of the neck can lead to further narrowing of the spinal canal and compression or blunt force upon the spinal cord. This often occurs in elderly people who fall and hit their head on an object, which causes bending of the neck to a position that is greater then their normal movement.

Non-traumatic spinal cord injury can be caused by various medical conditions or complications. This can include infection or inflammation (swelling) and exists in conditions such as multiple sclerosis, epidural abscess, transverse myelitis, poliomyelitis or HIV. Tumors can also lead to compression of the spinal cord. Vascular disorders are problems with the veins or arteries that supply the spinal cord and can lead to spinal cord injury. Injuries can also occur because of radiation therapy used to treat tumors located near the spinal cord. Many other conditions not listed here can lead to a non-traumatic spinal cord injury. .

What can happen at the cellular level of the spinal cord after trauma that can lead to damage of the spinal cord?

Multiple chemicals can be released at the area of the spinal cord injury that may lead to constriction or narrowing of the blood vessels that supply the spinal cord. This narrowing leads to ischemia (a lack of blood flow) to the spinal cord. The decrease in blood flow results in a decreased delivery of oxygen to the tissue of the spinal cord. This would most likely result in further damage to the spinal cord. The exact role that this plays in the ultimate damage to the spinal cord is unclear.

Edema (or swelling) can occur in the first days after a spinal cord injury at the site of injury. It is thought that this initially starts in the center area of the spinal cord and gradually spreads outward.

Within minutes after a spinal cord injury, there is an increase in the level of calcium at the site of injury within the spinal cord. This calcium increase reportedly reaches its highest level around eight hours after injury, but remains elevated for approximately one week. This increase in calcium can lead to complex chemical reactions that produce free radicals and other chemicals known to cause tissue injury.

Some degree of bleeding can also take place at the site of injury after trauma to the spinal cord. Normal blood contains iron, which is then released into the damaged area. This iron can further lead to chemical reactions that lead to tissue injury of the spinal cord.

Glutamate is one amino acid that has been released at the site of injury after trauma to the spinal cord. Glutamate can cause an increase in calcium which, as  described above, is a contributing factor to spinal cord tissue damage.

Specialized white blood cells (WBC) called neutrophils (polymorphonuclear granulocytes, PMN) are first to arrive at the site of injury. These are very important cells that normally help fight bacterial infections. In the case of trauma to the spinal cord, they also produce enzymes and free radicals that lead to tissue injury. This damage to the cells of the spinal cord is often referred to as a cytotoxic (toxic to the cell) injury. Other cells called macrophages also participate in the destruction of the spinal cord by destroying the coating (myelin) around the nerves by releasing an enzyme (although there is some debate about this involvement). These cells also play a potentially important role in recovery by increasing the cells that make myelin. Macrophages have other roles that may result in increasing substances that lead to nerve growth. Timeline after a spinal cord injury
First 24 hours
Within minutes of trauma to the spinal cord, there is evidence of damage to the small vessels within the spinal cord. Also, there is evidence of swelling in the cells that line the blood vessels within the spinal cord. Arteries develop local areas of enlargement and eventually burst within four to eight hours. Within 24 hours, small clots develop within some small blood vessels called capillaries. Nerve cells within the spinal cord begin to show evidence of death.

First Few Days
This period of time is characterized by various types of cells that continue to cause destruction but also by other cells that begin the rebuilding process.

Weeks to months
The previously mentioned macrophages begin to disappear from the injured area and are replaced by fluid filled pockets. The outer perimeter of the pockets is formed by scar tissue that was left over from the above destruction. Within three weeks from the time of injury, nerves began to dissolve in a process that is called “wallerian degeneration.”  When nerves dissolve and scar tissue forms, the spinal cord is unable to conduct electrical impulses through this area of the spinal cord, leading to a spinal cord injury.