A spinal cord injury (SCI) typically involves a sudden trauma to the spine that either fractures or dislocates vertebrae (ring-shaped bones of the spine). When these injuries occur, bone fragments, portions of disc material or damaged ligaments can cause bruising or tearing of the nervous tissue of the spinal cord. This can result in crushed or destroyed neurons (nerve cells) and axons (nerve fibers).

Neurons and axons of the spinal cord help coordinate movement and bodily functions and allow sensations to be felt. Neurons carry signals between the brain and the rest of the body. Axons help conduct outgoing signals from one neuron to other nerve, muscle or gland cells in the body. Axons also release neurotransmitters that affect these cells.

Injury to the spinal cord can result in impaired movement and sensation in the body. The extent of damage to neurons and axons after an SCI largely determines the severity of impairment a person experiences. The damage done to axons is responsible for most problems associated with SCIs.

The spinal cord is part of the central nervous system (CNS), which also contains the brain. The spinal cord does not extend the entire length of the spine. Instead, the length of the spinal cord is about 17 inches (43 centimeters) in women and 18 inches (45 centimeters) in men. The spinal cord begins at the base of the brain and ends in the lower back. The bony parts of the spine continue farther downward to what is known as the “tailbone.”  

The spine is made up of different segments: cervical (neck area), thoracic (upper back), lumbar (lower back), sacral (area near the pelvic bones) and coccygeal (base of spine, also known as the tailbone). There are a different number of bony vertebrae in each segment. The number changes from infancy to adulthood as some of the bones fuse together. Vertebrae surround the spinal cord and protect it from injury. The upper segments control areas of the upper body and lower segments control functioning of the lower parts of the body. The type of impairment sustained depends on where along the spinal cord the injury occurs, and on the type and severity of the injury.

Damage to the area continues even after the initial injury. Injuries often cause swelling of the spinal cord and surrounding areas. Bleeding and fluid accumulation may also occur. After trauma to the spine, nerve cells and axons in the spinal cord below the site of injury can slowly deteriorate and die. This disrupts the communication channel between the brain and body, inhibiting movement, sensation and bodily functions.

When communications throughout the body are cut off due to SCI, the patient's blood pressure is likely to drop. This can lead to spinal shock, a condition that disables parts of the spine that were not injured. The results can include paralysis that passes after several hours to days.

SCIs occur most often in the neck and lower back. In general, the higher up the spinal cord a person is injured, the more severe the injury is likely to be. For example, an injury at the level of the neck typically causes paralysis to both the upper and lower body, while an injury lower in the back may cause paralysis that is limited to the waist and below.

The nerves of the CNS do not regenerate after they are injured – unlike nerves elsewhere in the body. As a result, patients who experience damage to nervous tissue of the CNS may develop varying levels of paralysis. Paralysis can result from a complete severing of the patient’s spinal cord, although most SCIs do not completely sever the spinal cord.

The severity of damage affects a patient’s long-term prognosis. Some patients recover completely, while others may be paralyzed for life. People who suffer an SCI may not experience paralysis if they are treated promptly and the bones are stabilized and allowed to heal. Nonetheless, people with spinal cord injuries often experience lifelong disability.  

More than 200,000 Americans are living with SCIs, according to the National Institute of Neurological Disorders and Stroke (NINDS). Each year, more than 10,000 new cases of SCI occur, two-thirds of which strike people under 30.

Some patients with SCIs develop autonomic dysreflexia, episodes in which the blood vessels remain constricted. This can result in elevated blood pressure, which puts the patient at risk for stroke.

Other complications of SCIs may include:

• Bladder and bowel dysfunction
• Chronic pain
• Pressure sores (bed sores)
• Urinary tract infections
• Increased risk of respiratory and heart problems
• Deep vein thrombosis (blood clot deep within a muscle)
• Pulmonary embolism (blood clot that lodges in the lungs)
• Inability to sweat below the level of injury
• Infertility in men
• Reduced control of body temperature
• Sexual dysfunction
• Spasticity
• Weight loss or weight gain

Although SCIs remain a serious threat to a person’s long-term health, overall management has nonetheless improved in recent time. Until recent decades, patients with SCIs often died within a few weeks of injury due to infections and other related complications. Today, proper and prompt treatment allows many people with these injuries to survive and to lead much fuller lives than in the past.