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Spinal cord injury causes myelopathy or damage to white matter or myelinated fiber tracts that carry sensation and motor signals to and from the brain. [1][2]
It also damages gray matter in the central part of the spine, causing
segmental losses of interneurons and motorneurons. Spinal cord injury
can occur from many causes, including:
- Trauma such as automobile crashes, falls, gunshots, diving accidents, war injuries, etc.
- Tumor such as meningiomas, ependymomas, astrocytomas, and metastatic cancer.
- Ischemia resulting from occlusion of spinal blood vessels, including dissecting aortic aneurysms, emboli, arteriosclerosis.
- Developmental disorders, such as spina bifida, meningomyolcoele, and other.
- Neurodegenerative diseases, such as Friedreich's ataxia, spinocerebellar ataxia, etc.
- Demyelinative diseases, such as Multiple Sclerosis.
- Transverse myelitis, resulting from spinal cord stroke, inflammation, or other causes.
- Vascular malformations, such as arteriovenous malformation (AVM), dural arteriovenous fistula (AVF), spinal hemangioma, cavernous angioma and aneurysm.
[edit] Classification
The American Spinal Cord Injury Association
or ASIA defined an international classification based on neurological
levels, touch and pinprick sensations tested in each dermatome, and
strength of ten key muscles on each side of the body, i.e. shoulder
shrug (C4), elbow flexion (C5), wrist extension (C6), elbow extension (C7), hip flexion (L2). Traumatic spinal cord injury is classified into five types by the American Spinal Injury Association and the International Spinal Cord Injury Classification System.
- A indicates a "complete" spinal cord injury where no motor or
sensory function is preserved in the sacral segments S4-S5. Since the
S4-S5 segment is the lower segmental, absence of motor and sensory
function indicates "complete" spinal cord injury.
- B indicates an "incomplete" spinal cord injury where sensory but
not motor function is preserved below the neurological level and
includes the sacral segments S4-S5. This is typically a transient phase
and if the person recovers any motor function below the neurological
level, that person essentially becomes a motor incomplete, i.e. ASIA C
or D.
- C indicates an "incomplete" spinal cord injury where motor function
is preserved below the neurological level and more than half of key
muscles below the neurological level have a muscle grade of less than 3.
- D indicates an "incomplete" spinal cord injury where motor function
is preserved below the neurological level and at least half of the key
muscles below the neurological level have a muscle grade of 3 or more.
- E indicates "normal" where motor and sensory scores are normal.
Note that it is possible to have spinal cord injury and neurological
deficit with completely normal motor and sensory scores.
In addition, there are several clinical syndromes associated with incomplete spinal cord injuries.
- The Central cord syndrome is associated with greater loss of upper limb function compared to lower limbs.
- The Brown-Séquard syndrome
results from injury to one side with the spinal cord, causing weakness
and loss of proprioception on the side of the injury and loss of pain
and thermal sensation of the other side.
- The Anterior cord syndrome
results from injury to the anterior part of the spinal cord, causing
weakness and loss of pain and thermal sensations below the injury site
but preservation of proprioception that is usually carried in the
posterior part of the spinal cord.
- Tabes Dorsalis
results from injury to the posterior part of the spinal cord, usually
from infection diseases such as syphilis, causing loss of touch and
proprioceptive sensation.
- Conus medullaris syndrome results from injury to the tip of the spinal cord, located at L1 vertebra.
- Cauda equina syndrome is, strictly speaking, not really spinal cord injury but injury to the spinal roots below the L1 vertebra.
One can have spine injury without spinal cord injury. Many people
suffer transient loss of function ("stingers") in sports accidents or
pain in "whiplash" of the neck without neurological loss and relatively
few of these suffer spinal cord injury sufficient to warrant
hospitalization. In the United States, the incidence of spinal cord
injury has been estimated to be about 35 cases per million per year, or
approximately 10,500 per year (35 * 300). In China, the incidence of
spinal cord injury was recently estimated to be as high as 65 cases per
million per year in urban areas. If so, assuming a population of 1.3
billion, this would suggest an incidence of 84,500 per year (65 * 1300).
The prevalence of spinal cord injury is not well known in many large
countries. In some countries, such as Sweden and Iceland, registries
are available. About 450,000 people in the United States
live with spinal cord injury (one in 670), and there are about 11,000
new spinal cord injuries every year (one in 30,000). The majority of
them (78%) involve males between the ages of 16-30 and result from
motor vehicle accidents (42%), violence (24%), or falls (27%). This is
likely due to increased risk-taking behavior in men.
[edit] The Effects of Spinal Cord Injury
Divisions of Spinal Segments
 |
| Segmental Spinal Cord Level and Function |
| Level |
Function |
| Cl-C6 |
Neck flexors |
| Cl-Tl |
Neck extensors |
| C3, C4, C5 |
Supply diaphragm (mostly C4) |
| C5, C6 |
Shoulder movement, raise arm (deltoid); flexion of elbow (biceps); C6 externally rotates the arm (supinates) |
| C6, C7 |
Extends elbow and wrist (triceps and wrist extensors); pronates wrist |
| C7, T1 |
Flexes wrist |
| C7, T1 |
Supply small muscles of the hand |
| T1 -T6 |
Intercostals and trunk above the waist |
| T7-L1 |
Abdominal muscles |
| L1, L2, L3, L4 |
Thigh flexion |
| L2, L3, L4 |
Thigh adduction |
| L4, L5, S1 |
Thigh abduction |
| L5, S1, S2 |
Extension of leg at the hip (gluteus maximus) |
| L2, L3, L4 |
Extension of leg at the knee (quadriceps femoris) |
| L4, L5, S1, S2 |
Flexion of leg at the knee (hamstrings) |
| L4, L5, S1 |
Dorsiflexion of foot (tibialis anterior) |
| L4, L5, S1 |
Extension of toes |
| L5, S1, S2 |
Plantar flexion of foot |
| L5, S1, S2 |
Flexion of toes |
The exact effects of a spinal cord injury vary according to the type and level injury, and can be organized into two types:
- In a complete injury, there is no function below the
"neurological" level, defined as the lowest level that has intact
neurological function. If a person has some level below which there is
no motor and sensory function, the injury is said to be "complete".
Recent evidence suggest that less than 5% of people with "complete"
spinal cord injury recover locomotion.
- A person with an incomplete injury retains some sensation or
movement below the level of the injury. The lowest spinal cord level is
S4-5, representing the anal sphincter and peri-anal sensation. So, if a
person is able to contract the anal sphincter voluntarily
or is able to feel peri-anal pinprick or touch, the injury is said to
be "incomplete". Recent evidence suggest that over 95% of people with
"incomplete" spinal cord injury recover some locomotory ability.
In addition to a loss of sensation and motor function below the
point of injury, individuals with spinal cord injuries will often
experience other complications of spinal cord injury:
- Bowel and bladder function is regulated by the sacral
region of the spine, so it is very common to experience dysfunction of
the bowel and bladder, including infections of the bladder, and anal
incontinence.
- Sexual function is also associated with the sacral region, and is often affected.
- Injuries of the C-1, C-2 will often result in a loss of breathing, necessitating mechanical ventilators or phrenic nerve pacing.
- Inability or reduced ability to regulate heart rate, blood pressure, sweating and hence body temperature.
- Spasticity (increased reflexes and stiffness of the limbs).
- Neuropathic pain.
- Autonomic dysreflexia or abnormal increases in blood pressure, sweating, and other autonomic responses to pain or sensory disturbances.
- Atrophy of muscle.
- Superior Mesenteric Artery Syndrome
- Osteoporosis (loss of calcium) and bone degeneration.
- Gallbladder and renal stones.
[edit] The Location of the Injury
Knowing the exact level of the injury on the spinal cord is
important when predicting what parts of the body might be affected by
paralysis and loss of function.
Below is a list of typical effects of spinal cord injury by location
(refer to the spinal cord map to the right). Please keep in mind that
while the prognosis of complete injuries are predictable, incomplete
injuries are very variable and may differ from the descriptions below.
[edit] Cervical injuries
Cervical (neck) injuries usually result in full or partial tetraplegia (Quadraplegia).
Depending on the exact location of the injury, one with a spinal cord
injury at the cervical level may retain some amount of function as
detailed below, but are otherwise completely paralyzed.
- C3 vertebrae and above : Typically lose diaphragm function and require a ventilator to breathe.
- C4 : May have some use of biceps and shoulders, but weaker
- C5 : May retain the use of shoulders and biceps, but not of the wrists or hands.
- C6 : Generally retain some wrist control, but no hand function.
- C7 and T1 : Can usually straighten their arms but still may
have dexterity problems with the hand and fingers. C7 is generally the
level for functional independence.
[edit] Thoracic injuries
Injuries at the thoracic level and below result in paraplegia. The hands, arms, head, and breathing are usually not affected.
- T1 to T8 : Most often have control of the hands, but lack
control of the abdominal muscles so control of the trunk is difficult
or impossible. Effects are less severe the lower the injury.
- T9 to T12 : Allows good trunk and abdominal muscle control, and sitting balance is very good.
[edit] Lumbar and Sacral injuries
The effect of injuries to the lumbar or sacral region of the spinal canal are decreased control of the legs and hips, urinary system, and anus.
[edit] Central Cord and Other Syndromes
Central cord syndrome
(picture 1) is a form of incomplete spinal cord injury characterized by
impairment in the arms and hands and, to a lesser extent, in the legs.
This is also referred to as inverse paraplegia, because the hands and
arms are paralyzed while the legs and lower extremities work correctly.
Most often the damage is to the cervical or upper thoracic regions
of the spinal cord, and characterized by weakness in the arms with
relative sparing of the legs with variable sensory loss.
This condition is associated with ischemia, hemorrhage, or necrosis
involving the central portions of the spinal cord (the large nerve
fibers that carry information directly from the cerebral cortex).
Corticospinal fibers destined for the legs are spared due to their more
external location in the spinal cord.
This clinical pattern may emerge during recovery from spinal shock
due to prolonged swelling around or near the vertebrae, causing
pressures on the cord. The symptoms may be transient or permanent.
Anterior cord syndrome
(picture 2) is also an incomplete spinal cord injury. Below the injury,
motor function, pain sensation, and temperature sensation is lost;
touch, proprioception (sense of position in space), and vibration sense
remain intact. Posterior cord syndrome (not pictured) can also occur, but is very rare.
Brown-Séquard syndrome
(picture 3) usually occurs when the spinal cord is hemisectioned or
injured on the lateral side. On the ipsilateral side of the injury
(same side), there is a loss of motor function, proprioception,
vibration, and light touch. Contralaterally (opposite side of injury),
there is a loss of pain, temperature, and deep touch sensations.
[edit] Treatment
Treatment for acute traumatic spinal cord injuries have consisted of giving a high dose methylprednisolone
if the injury occurred within 8 hours. The recommendation is primarily
based on the National Acute Spinal Cord Injury Studies (NASCIS) II and
III. Some of the claims of the studies have been challenged as being
from faulty interpretation of the data.
Scientists are investigating many promising avenues of treatment for
spinal cord injury. Thousands of articles in the medical literature
describe work, mostly in animal models, aimed at reducing the
paralyzing effect of injury to the spinal cord and promoting regrowth
of functional nerve fibers. Despite the devastating effects of the
condition, commercial funding for spinal cord cure research is limited,
owing primarily to the small size of the population of potential
beneficiaries. Despite this, a number of experimental treatments have
reached controlled human trials. In addition, nerve protection and
regeneration strategies are being studied in more common conditions
like Alzheimer's Disease, Parkinson's Disease, Amyotrophic Lateral Sclerosis and Multiple sclerosis. There are many similarities between these neurodegenerative diseases and spinal cord injury, and this research adds considerable new information relevant to spinal cord injury treatment.
Advances in the science of spinal cord injury treatment are
newsworthy, and considerable media attention is drawn towards new
developments. Aside from the use of methylprednisolone, none of these
developments have reached even limited use in the clinical care of
human spinal cord injury. Around the world, proprietary centers
offering stem cell
transplants and treatment with neuroregenerative substances are fueled
by glowing testimonial reports of neurological improvement. Independent
validation of the results of these treatments is lacking.[3]
[edit] See also
[edit] External links
| [show]
Nerves: spinal nerves |
|
| Cervical (8) |
C1, C2, C3, C4, C5, C6, C7, C8
anterior ( Cervical plexus, Brachial plexus) - posterior ( Posterior branches of cervical nerves, Suboccipital - C1, Greater occipital - C2, Third occipital - C3)
|
|
| Thoracic (12) |
T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12
anterior ( Intercostal, Intercostobrachial - T2, Thoraco-abdominal nerves - T7-T11, Subcostal - T12) - posterior ( Posterior branches of thoracic nerves)
|
|
| Lumbar (5) |
|
|
| Sacral (5) |
|
|
| Coccygeal (1) |
|
|
