What is a Spinal Cord Injury?
- Causes of Cord Damage
- What is the Spinal Cord?
- What are the Vertebrae?
- Effects of Injury
- Levels of Injury
Spinal Cord Injury Overview
A spinal cord injury (SCI) is caused by damage or trauma to the spinal cord that results in a loss or impaired function causing reduced mobility or sensation.
Common causes of damage to the spinal cord are:
- Trauma: car accident, gunshot, falls, assult, sports injuries, etc.
- Disease: transverse myelitis, polio, spina bifida, Friedreich's ataxia, cancer, stroke, 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 resulting from compression or inflammation results in the loss of function. An 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 affected 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 tightly compacted nerves contained within the vertebral column that carry nerve impulses to and from the brain throughout 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 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 vertically downwards through the middle of the spinal column to around the waist. The pathways that are situated within the spinal cord are called upper motor neurons (UMN's). Their function is to carry messages back and forth from the brain 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 between each vertebra 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 spinal cord and upwards via ascending spinal tracts to the brain. The motor portions of the LMN receive messages from the brain via descending tracts in the spinal cord to initiate actions such as muscle movement, gland functions and certain internal organ commands.
What are the Vertebrae?
The spinal cord is surrounded by a hollow column of bones called vertebrae. These bones constitute the spinal column (back bones and neck bones). Generally the higher in the spinal column the spinal cord injury occurs, the more physical impairment a person will experience resulting in an increased level of paralysis. The vertebra are named according to their location. The seven vertebrae in the neck are called the cervical vertebrae. The top vertebra is called C1 or atlas vertebra and connects the top of the spinal column to the skull. The bottom cervical vertebra is called C7. Cervical SCI's usually result in loss of function in the arms and legs resulting in tetraplegia which is also referred to as quadriplegia. The next twelve vertebra are called the thoracic vertebra, T1-T12. The first thoracic vertebra T1 is the vertebra where the top rib attaches. There are 5 lumbar vertebrae, one fused sacral vertebra and one fused coccygeal vertebra.
So to recap, the five sections of the vertebral column are:
- Cervical vertebrae: C1-C7
- Thoracic vertebrae: T1-T12
- Lumbar vertebrae: L1-L5
- Sacrum: 5 vertebrae fused into one bone.
- Coccyx: 4 vertebrae fused into one bone.
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 resulting in tetraplegia (quadriplegia). 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 are the lumbar vertebra. The sacral vertebra run from the pelvis to the end of the spinal column. Injuries to the five lumbar vertebra (L1 thru L5) and similarly to the five sacral vertebra (S1 thru S5) generally result in varying loss of function in the hips, legs, bladder, bowel and sexual function.
The spinal cord ends between L1-L2 where a mass of spinal nerves continue downwards inside the lumbar (L2-L5) and sacral (S1-S2) vertebrae. This mass of spinal nerves is referred to as the cauda equina and damage to these nerve roots is referred to as cauda equina syndrome.
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 results in no function below the level of neurological injury: no sensation and no voluntary movement. Both sides of the body are equally affected. An incomplete injury results in some preserved function below the level of neurological 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 function on one side of the body than the other.
Types of incomplete spinal cord injury are:
- Anterior Cord Syndrome
- Brown Sequard Syndrome
- Central Cord Syndrome
- Posterior Cord Syndrome
With the recent advances in medical intervention and treatment of acute SCI, incomplete injuries are becoming more common. The most frequent spinal cord injury neurological classifications at time of discharge (2014) from a spinal injury centre is incomplete tetraplegia (31.6%), followed by incomplete paraplegia (18.6%), complete paraplegia (24.6%) and complete tetraplegia (19.3%). 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 resulting in loss of function. Remember that in incomplete injuries there can be a wide variation in the 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. Diaphragm pacemaker devices may be required to stimulate the phrenic nerve to initiate a persons breathing due to weak innervation of the diaphragm. C5 injuries often result in shoulder (deltoid) and biceps control, but no control of the wrist or hand. C6 injuries generally yield wrist control (wrist extensors), but no finger hand function. Individuals with C7-T1 injuries can straighten their arms (triceps) but still may have dexterity problems with the hand and fingers.
It is interesting to note that in the cervical area of the spine the nerve roots exit the spinal column above the vertebra, except for C7 where a pair of nerve roots also exit both above and below the vertebra. This is why there are seven cervical vertebrae but eight pairs of cervical nerve roots, C1-C8. From T1 downwards all spinal nerves then exit the spinal column below the vertebrae.
Injuries at the thoracic level and below result in paraplegia, with the hands not affected. At T1 to T8 whilst there is good control of the hands, trunk control may vary as the result of lack of abdominal muscle control. Lower thoracic injuries (T9 to T12) 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.
To reference the spinal segments discussed above, the 5 spinal segments are:
- Cervical segments: C1-C8
- Thoracic segments: T1-T12
- Lumbar segments: L1-L5
- Sacral segments: S1-S5
- 1 coccygeal spinal nerve (sensation only).
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