It’s a cruel irony that the man best known for playing Superman is the most famous American living with a spinal cord injury. Christopher Reeve is joined by countless thousands whose lives have been dramatically altered by accidents associated with cars, motorbikes, guns, and sports, especially diving.

An estimated 10,000 spinal cord injuries occur each year in the United States, most often striking active young adults. Persons between 16 and 30 years of age account for 55 percent of all spinal cord injuries and men are four times as likely as women to be injured.

The spinal cord is a long rope-like extension from the brain reaching down the back to the waist. It acts as the communication system carrying messages from the brain to all parts of the body (kick the ball) and back again (ouch I hurt my toe).

The spinal cord is surrounded and protected by the vertebrae that make up the spinal column. Grey matter, a core of motor and sensory neurons, makes up the innermost part of the spinal cord. White matter, consisting of long axons sheathed in myelin, an insulating material, forms a cylinder around the grey matter. Axons branch from the white matter into the grey matter, making contact with the motor neurons that in turn relay signals to muscles.

The severity and extent of a spinal cord injury depends on where the cord is severed or damaged. The higher the site of injury, the more severe the damage.

When the injury occurs in the area of the seven cervical vertebrae (in the area of the neck), quadriplegia often occurs, interfering with all body movement and function below the shoulders.

Damage to the 12 thoracic vertebrae (at the chest level) can cause paraplegia, paralysis and loss of feeling from the waist down. Damage to the lumbar vertebrae in the lower back causes loss of function in the hips and legs.

Multiple Research Paths
A great deal of research in recent years has focused on attempting to repair spinal cord injuries by trying to get the long axons to cross the gap of severed or injured tissue and reconnect with healthy tissue on the other side.

A number of obstacles have to be overcome, however. After a spinal cord injury, specialized glial cells clump together to form scar tissue at the injury site. This glial scar tissue is particularly difficult for axons to cross.

Scientists have recently discovered that it’s not just the glial scar tissue that is hindering regeneration, however. They now know that, during their normal growth phase, neurons receive an outside signal that instructs them to slow the axon growth and concentrate on development of dendrites, the smaller pathways that branch out from the axons. The molecules that block axon regeneration are known as Nogo.

Yale researchers have developed a synthetic peptide that promotes nerve fiber growth in rats and allows them to regain at least partial use of their limbs. The peptide binds to the Nogo receptor and prevents it from doing its normal job. This approach has shown some promise in animal studies but human trials are still a long way off.

A team of scientists from the University of Wisconsin, Madison, have shown that embryonic stem cells are capable of developing into healthy, neural cells after being implanted into the brains of mice. This is an important step for stem cell technology which has the potential for creating a virtually unlimited supply of neural cells that might be transplanted to repair anything from spinal cord injuries to Parkinson’s disease. But this technology is still some years away from human trial stage.

In Florida, researchers have transplanted fetal tissue into the injured spinal cords of two patients. Transplantation of fetal spinal cord tissue has resulted in partial restoration of function in laboratory animals, and researchers hope that in the coming decades this technique will be refined in humans.

An Israeli researcher has treated a small number of patients soon after a paralyzing spinal cord injury and succeeded in restoring feeling and some voluntary movement in legs. The treatment, which must be administered within 14 days of injury, involves injecting macrophages, inflammatory cells of the immune system, to the injury site. More patients and a longer waiting period will be necessary to see how successful this approach will be.

Limiting the Damage
The primary emphasis after a spinal cord injury is to prevent secondary damage. Within hours of injury the damaged cells, axons and blood vessels release a cascade of toxic chemicals, killing healthy neighboring cells. Even days or weeks after the initial injury a wave of cell suicide, a process known as apoptosis, can overwhelm nearby cells.

High doses of the steroid methylprednisolone within eight hours of the injury have been used for the past decade to minimize secondary damage. The steroid has unwanted side effects, and considerable research is focused on other drugs that can reduce swelling, maintain blood supply to the spinal cord and promote clean up of the debris around the injury site.

For those who have lived with spinal cord injuries for many years, advances in rehabilitation offer hope for a better quality of life. A patient’s limbs and organs as well as spinal cord tissue below an injury are often healthy and essentially unharmed. Scientists have discovered that some functions are hard wired into tissue and may be able to be reproduced even in the absence of commands from the brain. If given the necessary support, such as a harness, some people can be trained to step on a treadmill when the spinal cord is activated with electrical stimulation. Although it’s not normal walking, this type of therapy can reduce wheelchair-related complications such as bone loss, muscle atrophy and pressure sores.

Oklahoma researchers have succeeded in allowing a wheelchair-dependent man to walk up to 1000 feet at a time using only a walker. This technique requires a great deal of physical effort and discipline over an extended training and strengthening period. After intensive physical preparation a small device is surgically inserted into the lower back that stimulates the spinal cord using low level electrical current directed by a remote device.

Although it doesn’t eliminate the need for a wheelchair, it does make this individual far more independent in his own home and on short outings. This approach is expensive and time consuming and considered best suited to patients with incomplete spinal cord injuries, good upper body strength and a high degree of motivation.

For those with spinal cord injuries, advances in research seem painfully slow. The reality is that progress is made in small increments and that more attainable improvements can result in a major boost to quality of life. Being able to restore function to just a few segments of the spinal cord may allow a patient to come off a ventilator or to regain use of his arms. Knowledge is advancing simultaneously on many fronts and the next decade will bring tangible benefits.

REFERENCES:
“Clonal Human Neurons Reestablish Connections in Rats,” Pain and Central Nervous System Week, July 29, 2002.
“Could the Future of Rehab Include Walking Paraplegics, Quadriplegics?” Rehab Continuum Report, June 2002.
Helen Frankish, “Spinal Cord Repair Moves a Step Closer,” The Lancet, April 13, 2002.
Nicola Jones, “Coming Together,” New Scientist, April 28, 2001.
John McDonald and Cristina Sadowsky, “Spinal- Cord Injury,” The Lancet, February 2, 2002.
“Peptide Promotes Nerve Growth,” Drug Discovery and Technology News, June 2002.
“Rebuilding the Spinal Cord,” Business Week, December 11, 2000.
“Regenerating Neural Connections Restores Walking Ability in Disabled Rats,” Pain and Central Nervous System Week, July 14, 2001.
“Researchers Develop Peptide that Promotes New Cord Growth in Animals,” Pain and Central Nervous System Week, June 17, 2002.
“Sparking Angiogenesis Soon After Injury May Ignite Locomotor Revival,” Pain and Central Nervous System Week, June 24, 2002.
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“Stanford Explores New Avenue for Brain Injury, Paralysis Research,” Pain and Central Nervous System Week, July 22, 2002.
Lise Stevens and Richard Glass, “Neck Injuries,” JAMA, October 17, 2001.
David Stocum, “Regenerating the Spinal Cord,” World and I, February 2001.
“Toward the Final Assault,” Paraplegia News, January 2000.