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What is a Spinal Cord Injury?

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Spinal Cord Injury Overview

spinal cord injury

A Spinal Cord Injury (SCI) is damage or trauma to the spinal cord that results in a loss or impaired function causing reduced mobility or sensation. Common causes of damage are trauma (car accident, gunshot, falls, sports injuries, etc.) or disease (Transverse Myelitis, Polio, Spina Bifida, Friedreich's Ataxia, etc.). The spinal cord does not have to be severed in order for a loss of function to occur. In most people with SCI, the spinal cord is intact, but the cellular damage to it results in loss of function. SCI is very different from back injuries such as ruptured disks, spinal stenosis or pinched nerves. The later involves musculoskeletal and peripheral nerve changes where as a spinal cord injury involves damage to the central nervous system.

It is possible for a person to "break their back or neck" yet not sustain a spinal cord injury as long as only the bones (the vertebrae) around the spinal cord are damaged, but the spinal cord is not affected. In such cases the person may not experience paralysis after the vertebrae are stabilised. Fractured vertebrae and dislocated vertebrae can be stabilised using surgical management such as traction, vertebral fusion, fixation using titanium plates or rods and for less severe fractures of the vertebra bed rest.

What is the Spinal Cord?

The spinal cord is the major bundle of nerves that carry nerve impulses to and from the brain to the rest of the body. The brain and the spinal cord constitute the central nervous system. Motor and sensory nerves outside the central nervous system constitute the peripheral nervous system, and another diffuse system of nerves that control involuntary functions such as blood pressure and temperature regulation are the sympathetic and parasympathetic nervous systems.

The spinal cord is about 18 inches in length and extends from the base of the brain surrounded by vertebral bodies, extending vertically down the middle of the back, to about the waist. The nerves that are situated within the spinal cord are called upper motor neurons (UMN's) and their function is to carry the messages back and forth from the brain to the spinal nerves along spinal tracts within the spinal cord responsible for specific functions.  The spinal nerves that branch out from the spinal cord to parts of the body are peripheral nerves called lower motor neurons (LMN's). These spinal nerves exit and enter at each vertebral level and communicate with specific areas of the body. The sensory portions of the LMN carry messages about sensation from the skin and muscles such as pain, temperature, joint position and information from organs to the brain. The motor portions of the LMN send messages from the brain to the various body parts to initiate actions such as muscle movement, gland functions and certain internal organ commands.

What are the Vertebrae?

The spinal cord is surrounded by rings of bone called vertebra. These bones constitute the spinal column (back bones). In general, the higher in the spinal column the injury occurs, the more dysfunction a person will experience resulting in an increased level of paralysis. The  vertebra are named according to their location. The seven vertebra in the neck are called the cervical vertebra. The top vertebra is called C-1, the next is C-2, etc. Cervical SCI's usually cause loss of function in the arms and legs, resulting in quadriplegia. The twelve vertebra in the chest  are called the thoracic vertebra. The first thoracic vertebra, T-1, is the vertebra where the top rib attaches. There are 5 lumbar vertebrae, and one fused sacral vertebra.

What are the Effects of a Spinal Cord Injury?  

An injury to the spinal cord segments contained within the cervical spinal vertebrae C1-C7 usually result in paralysis of all four limbs to some degree. Injuries in the thoracic region usually affect the chest and the legs and result in paraplegia. The vertebra in the lower back between the thoracic vertebra, where the ribs attach, and the pelvis (hip bone), are the lumbar vertebra. The sacral vertebra run from the pelvis to the end of the spinal column. Injuries to the five Lumbar vertebra (L-1 thru L-5) and  similarly to the five Sacral Vertebra (S-1 thru S-5) generally result in loss of functioning in the hips, legs, bladder, bowel and sexual function.

The effects of SCI depend on the type of injury and the level of the injury. SCI can be divided into two types of injury - complete and incomplete. A complete injury means that there is no function below the level of the injury; no sensation and no voluntary movement. Both sides of the body are equally affected. An incomplete injury means that there is some functioning below the primary level of the injury. A person with an incomplete injury may be able to move one limb more than another, may be able to feel parts of the body that cannot be moved, or may have more functioning on one side of the body than the other. With the recent advances in medical intervention and treatment of acute SCI, incomplete injuries are becoming more common. Since 2010, the most frequent spinal cord injury neurological classifications at time of discharge from a spinal injury center is incomplete tetraplegia (40.6%), followed by incomplete paraplegia (18.7%), complete paraplegia (18.0%) and complete tetraplegia (11.6%). It is estimated that less than 1% of individuals diagnosed with a spinal cord injury experienced a complete neurological recovery at the time of hospital discharge. Over the last 20 years, the incidence of individuals with incomplete tetraplegia has increased whilst complete paraplegia and complete tetraplegia have decreased.

Spinal Cord Injury Levels

The level of injury is very helpful in predicting what parts of the body might be affected by paralysis and loss of function. Remember that in incomplete injuries there will be some variation in these prognoses.

Cervical (neck) injuries usually result in Quadriplegia/Tetraplegia. Injuries to the spinal cord segments above the C4 level (C1,C2, C3) may result in the need of breathing aids such as mechanical ventilators or diaphragm pacemakers to stmulate the phrenic nerve to initiate a persons breathing due to weak innervation of the diaphragm. C-5 injuries often result in shoulder (deltoid) and biceps control, but no control of the wrist or hand. C-6 injuries generally yield wrist control (wrist extensors), but no finger hand function. Individuals with C-7 and T-1 injuries can straighten their arms (triceps) but still may have dexterity problems with the hand and fingers. Injuries at the thoracic level and below result in paraplegia, with the hands not affected. At T-1 to T-8 there is most often control of the hands, but poor trunk control as the result of lack of abdominal muscle control. Lower T-injuries (T-9 to T-12) allow good truck control and good abdominal muscle control. Sitting balance is very good. Lumbar and Sacral injuries yield decreasing control of the hip flexors and legs.

Paralysis also has other effects as well as a loss of sensation or motor function. Individuals with SCI also experience other neurological changes. For example, the person may experience dysfunction of the bowel and bladder. Sexual function is frequently affected in men with SCI as they may have their fertility affected due to the inability to attain an erection or achieve ejaculation, while women's fertility is generally not affected. Other effects of SCI may include low postural blood pressure (Postural Hypotension), inability to regulate blood pressure effectively , reduced control of body temperature (poikilothermic), inability to sweat below the level of injury, and chronic pain.

spinal cord injury levels



The above information has been written with reference from the following sources:


Sekhon, Lali H.S.; Fehlings, Michael G. (2001). "Epidemiology, Demographics, and Pathophysiology of Acute Spinal Cord Injury". Spine 26 (24 Suppl): S2–12. doi:10.1097/00007632-200112151-00002. PMID 11805601.
Alexander Vaccaro; Michael Fehlings (2010). Spine and Spinal Cord Trauma: Evidence-Based Management. Thieme Publishers. ISBN 9781604062229. Retrieved 2012-05-06.

Updated: May 2014


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